Colloids and Surfaces A Physicochem. Eng. Aspects 317

Colloids and Surfaces A:Physicochem.Eng.Aspects 471(2015)45–53Contents lists available at ScienceDirectColloids and Surfaces A:Physicochemical andEngineeringAspectsj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c o l s u r faWater-soluble complexes of hydrophobically modified polymer and surface active imidazolium-based ionic liquids for enhancing oil recoveryShaohua Gou a ,b ,∗,Ting Yin b ,Liwei Yan b ,Qipeng Guo c ,∗∗aState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,PR ChinabOil &Gas Field Applied Chemistry Key Laboratory of Sichuan Province,School of Chemistry and Chemical Engineering,Southwest Petroleum University,Chengdu 610500,PR China cPolymers Research Group,Institute for Frontier Materials,Deakin University,Locked Bag 2000,Geelong,Victoria 3220,Australiah i g h l i g h t s•A series of copolymer/ionic liquidscomplexes (PAAD/ILs)were used for EOR.•PAAD/C 8mimBr complex can effec-tively reduce the IFT of water/crude oil.•PAAD/C 8mimBr complex with NaCl can further reduce IFT of water/crude oil.•PAAD/C 8mimBr complex exhibits excellent temperature resistance.•PAAD/C 8mimBr complex can enhance oil recovery as high as 21.65%.g r a p h i c a la b s t r a cta r t i c l ei n f oArticle history:Received 20October 2014Received in revised form 27January 2015Accepted 2February 2015Available online 16February 2015Keywords:Ionic liquidsHydrophobically associating copolymer Interfacial tensionEnhancing oil recoverya b s t r a c tThe current study introduces the water-soluble complexes containing hydrophobically associating copolymer and a series of surface activity imidazolium-based ionic liquids (C n mimBr,n =6,8,10,12,14and 16).The polymer,denoted as PAAD,was prepared with acrylamide (AM),acrylic acid (AA)and N ,N -diallyl-2-dodecylbenzenesulfonamide (DBDAP).And the hydrophobic associative behavior of PAAD was studied by a combination of the pyrene fluorescence probe and viscosimetry.Incorporation of C n mimBr (n =10,12,14and 16)in PAAD leaded to the white thick gel,while the pellucid solutions were obtained in complexes of PAAD and C n mimBr (n =6and 8);addition of C 6mimBr around critical micelle concen-tration resulted in a large decrease in viscosity of solution.Therefore,we particularly investigated the performance of PAAD/C 8mimBr complex.The interfacial tension of PAAD/C 8mimBr complex solution and crude oil under different conditions was examined.Moreover,PAAD/C 8mimBr complex exhibited∗Corresponding author at:School of Chemistry and Chemical Engineering,South West Petroleum University,Xindu Avenue 8#,Xindu,Chengdu 610500,Sichuan,PR China.Tel.:+8602883037301;fax:+8602883037333.∗∗Corresponding author at:Polymers Research Group,Institute for Frontier Materials,Deakin University,Locked Bag 2000,Geelong,Victoria 3220,Australia.E-mail addresses:shaohuagou@ (S.Gou),qguo@.au (Q.Guo)./10.1016/j.colsurfa.2015.02.0220927-7757/©2015Elsevier B.V.All rights reserved.46S.Gou et al./Colloids and Surfaces A:Physicochem.Eng.Aspects471(2015)45–53superior temperature resistance and shear reversible performance for enhancing oil recovery(EOR)byrheological test.The promising EOR of21.65%can be obtained by PAAD/C8mimBr complex showing highpotential to utilize this kind of new complex in EOR processes.©2015Elsevier B.V.All rights reserved.1.IntroductionIn fact,with the recovery of the reservoirs all over the world, most crude oil is trapped in the reservoirs after using the conven-tional oil production methods.High world energy demands make the efficient enhancing oil recovery(EOR)techniques have never become as urgent as today[1].Generally,chemical enhancing oil recovery methods are of specific concern in oil recovery,like poly-merflooding,surfactantflooding and polymer–surfactantflooding [2–4].One of the most promising chemical EOR techniques is the polymer–surfactantflooding.The main mechanism of this method is based on the large mobility ratio and the low interfacial tension between the displacementfluid and crude oil.Generally,a lager capillary number(Nc)and/or a lower mobility ratio(M)result in a higher oil recovery,and the most effective way of increasing the Nc is reducing interfacial tension between the displacementfluid and crude oil[1].Hydrophobically associating polymer is a special kind of water-soluble polymer which contains a small amount of hydrophobic monomer[5].This kind of polymer has received increasing atten-tions on account of its unique rheological performance[6].Due to the hydrophobic groups it can generate the intramolecular and intermolecular hydrophobic microarea leading to a considerable increase of viscosity,consequently improving the mobility ratio (M).It has been demonstrated that the performance can be notably changed by combinations of this polymer solution with a certain amount of surfactant[7–9].Although the hydrophobically asso-ciating polymer–surfactantflooding technique is promising,its application to date has been limited due to the rheology perfor-mance of system and the failure in function of surfactant under the reservoir conditions such as poor salt tolerance of anionic surfactant[10].For these reasons,there is growing interest infind-ing a new hydrophobically associating polymer–surfactant system whose properties bestfit the EOR requirements.Ionic liquids(ILs)are liquids at ambient that have unique fea-ture such as high thermal stability,negligible vapor pressure,and favorable chemical stability[11,12].Recently,the incorporation of ionic liquid into polymers has attracted much interest,such as poly-mer/ionic liquid gel membranes with high ionic conductivity and mechanical stability[13],and the thermodynamic phase behav-ior of polymer solution in the presence of different kinds of ILs [14,15].The surface active ILs,imparts them unique physicochemical properties:analogous to common surfactants,they have surface activity.It seems to be a few investigations on the interfacial ten-sion(IFT)of ILs solution/oil system were reported[10,16–21].Those authors recognized its desired behavior at high salinity and tem-perature.Imidazolium based surface active ILs are readily available in technical quantities and these kinds of ILs are one of the com-mon ILs among the ILs families[22,23].Hezave et al.[18]examined the IFT of1-dodecyl-3-methylimidazolium chloride with crude oil under different conditions and performed the coreflooding experiments.They found promising results of both enhanced oil recovery efficiency and adsorption on the rock surfaces.Above investigations show high potential to utilize imidazolium based ILs to replace the traditional surfactants in EOR processes to reduce the IFT.However,few studies are available on incorporation of these surface active ILs into hydrophobically associating polymer for EOR.Based on thesefindings,we report a study on the complexes of the long-chain imidazolium based surface active ILs C n mimBr (n=6,8,10,12,14,and16)and hydrophobically modified polymer denoted as PAAD which was prepared by acrylamide(AM),acrylic acid(AA)and N,N-diallyl-2-dodecylbenzenesulfonamide(DBDAP). According to our previous work[24],the introduction of sulfo-namide structure and aromatic ring can improve the rigidity of the polymer chains exhibiting high-temperature resistance,and based on this,DBDAP containing above structures and long chain structure was designed to prepare the hydrophobically associating polymer to further improve the performance of the polymer.ILs can interact with this polymer by electrostatic force and they can also form micelle-like clusters associated with the polymer hydropho-bic plementary hydrophobic associative behavior data of PAAD obtained by pyrene probefluorescence and viscosimetry were also presented.The IFT of PAAD/C8mimBr complex solution and crude oil under different conditions was measured,and the rheological behavior of the complex was also investigated.TG-DSC was also carried out to study the thermal decomposition of the complex.Moreover,the coreflooding test was conducted.2.Experimental2.1.MaterialsAcrylamide(AM),acrylic acid(AA),dodecylbenzene sulfonic acid(DB),thionyl chloride(SOCl2),diallylamine(DAP),nonaphenol polyethyleneoxy(10)ether(OP-10),N-methylimidazole(mim),1-bromobutane,1-bromohexane,1-bromooctane,1-bromodecane, 1-bromododecane,1-bromotetradecane,1-bromohexadecane, cetyltriethylammonium bromide(CTAB),triethylamine(Et3N), dichloromethane(CH2Cl2),trichloromethane(CHCl3),ethyl acetate,diethyl ether,ammonium persulfate((NH4)2S2O8), sodium bisulfite(NaHSO3),NaCl,and NaOH etc.are all provided by Chengdu Kelong Chemical Reagent Factory,Sichuan.These chemicals are chemically pure or above.CHCl3,ethyl acetate, Et3N and diethyl ether were dried using anhydrous sodium sulfate before used,and other chemicals were used as commercial without further purification.2.2.Synthesis of DBDAPN,N-Diallyl-2-dodecylbenzenesulfonamide(DBDAP)was pre-pared referring to the traditional methods[25].Briefly,dode-cylbenzenesulfonyl chloride was prepared by DB with excess SOCl2under reflux at50◦C for5h.And the reaction of dode-cylbenzenesulfonyl chloride and DAP using Et3N as acid binding agent in CH2Cl2was performed at0–5◦C for6h.The product was washed three times with1wt%diluted hydrochloric acid, 1wt%sodium hydroxide and saturated salt water,respectively, and then the solvent was removed under a vacuum.Obtained DBDAP was brown liquid with a yield of92%.DBDAP:1H NMR (400MHz,CDCl3):ı=7.76(d,2H,J=7.2Hz,Ar H),7.07(d,2H, J=8.0Hz,Ar H),5.77–5.81(m,2H,CH2C H CH2), 5.13–5.32 (m,4H,C H2CH CH2),3.15–3.19(m,4H,SO2N(C H2)2),2.46 (t,2H,J=8.0Hz,Ar C H2),1.47–1.57(m,2H,Ar CH2C H2), 1.20–1.24(m,18H,Ar CH2CH2(C H2)9CH3),and0.87(t,3H, J=4.0Hz,C H3CH2),ppm.S.Gou et al./Colloids and Surfaces A:Physicochem.Eng.Aspects471(2015)45–5347Scheme1.The synthetic process of PAAD.2.3.Synthesis of PAADPreparation of PAAD was conducted via free radical copolymer-ization of AM,AA and DBDAP in aqueous solution with emulsifier OP-10.DBDAP(0.02g),AM(6g),AA(4g)and OP-10(0.1g)were dissolved in40mL deionized water with a magnetic stir bar,and the pH was adjusted around7using1.0mol/L NaOH solution. Then,(NH4)2S2O8(0.0368g)and NaHSO3(0.0132g)were added in at40◦C for8h under N2atmosphere.The resulting product was obtained by repeatedly washed with ethanol and dried at40◦C,and then kept in a desiccator.The synthetic process of PAAD is shown in Scheme1.2.4.Synthesis of PAAD/ILs complexSurface active ILs,C n mimBr,n=6,8,10,12,14and16,were prepared and purified as reported in literature[23,26].The water content of ILs is controlled by drying them at100◦C under vacuum conditions.A desired amount of PAAD was dissolved in distilled water under mechanical stirring until a clear homogeneous solu-tion was obtained.Then,the above ILs with definite concentration were added to the prepared polymer solution at50◦C for4h. Finally,the complex solutions of polymer and different ILs were obtained.2.5.CharacterizationFTIR spectra were determined with the KBr pellets method using WQF-520Fourier transform infrared spectrometer in the optical range400–4000cm−1by the averaging of32scans(Bei-jing Rayleigh Analytical Instrument Corporation,China).1H NMR spectra were recorded on a Bruker AV III-400NMR spectrometer (Bruker,Switzerland)in D2O or CDCl3.The intrinsic viscosity of copolymer was measured with a Ubbe-lohde viscometer using1mol/L NaCl aqueous solution as the solvent with the dilution extrapolation method at30.0±0.1◦C, and the initial concentration of copolymer was0.001g/mL (C0=0.001g/mL).The viscosity-average molecular weight of copolymer can be calculated from the intrinsic viscosity value by employing Mark–Houwink equation.However,it should be pointed out that this measurement is an approximate and relative method on the determination of the viscosity-average molecular weight of hydrophobically associating polymers due to the effect of intra-molecular hydrophobic interaction.2.6.Apparent viscosity measurementThe apparent viscosity of different solutions was obtained on a Brookfield D-III+Pro viscometer(Brookfield,USA)with different viscometer rotors0#(6.0rpm)62#(18.8rpm)and63#(27.3rpm).2.7.Pyrenefluorescence probeThefluorescence intensities of copolymer were measured with a Shimadzu RF-5301PC Fluorescence spectrophotometer with excitation at335nm,with a slit width of5nm and in a spectral range350–550nm.The different concentrations of copolymer solu-tions with pyrene were prepared with redistilled water,and the concentration of pyrene was about1.25×10−6mol/L.The ratios (I1/I3)of the strength of thefirst peak to that of the third peak in fluorescence spectra were calculated.2.8.Thermogravimetry and differential scanning calorimetryThe water of PAAD/C8mimBr complex solution with a cer-tain mass ratio was removed through rotary evaporation to test with thermogravimetry and differential scanning calorimetry(TG-DSC)using a STA449F3synchronous thermal analyser(Netzsch, Germany)in the temperature range40–700◦C at a heating rate of 10◦C/min under air atmosphere.2.9.Rheological experimentsThe effect of temperature on the viscosity of samples was mea-sured by HAAKE RS600Rotational Rheometer(HAAKE,Germany) at shear rate of170s−1to simulate injection rate at the heating rate of3◦C/min from30to120◦C.The shear thinning behavior of samples was performed in the range of2–500s−1shear rates at 30◦C.2.10.Interfacial tension testSurface tension measurements were performed with TX500C SpinningDrop Interface tensiometer(CNG USA Co.)using the drop volume method at30◦C.The oil used in interfacial tension test is prepared by crude oil and kerosene with a mass ratio of2:1,and the density is0.8982g/cm3.The crude oil sample is obtained from Bohai Suizhong Oilfield(SZ36-1CEPK).Then,the interfacial tension was measured applying a rotating velocity of5000rpm.The density of each system was measured.2.11.Coreflooding testCoreflooding test was using stainless steel packed with sand (30cm in length and2.55cm in diameter,approximately),and the size distribution of sand was80–100items.The apparent viscos-ity of simulated crude oil was30.6mPa s at70◦C.NaCl solution was injected in core until a steady pressure to obtain the porosities of core by gravimetry,and permeability was obtained by injecting NaCl solution at a constant rate of9.99mL/min using Darcy’s law [27].The sand with crude oil has been saturated at0.1mL/min at 70◦C for96h,and oil saturation was calculated[4].Firstly,the waterflooding was conducted with the NaCl solution until water cut reached at95%,and then it wasflooded with0.2PV cumulative injection volume of chemicals.Finally,the extrapolated waterflooding was conducted with the NaCl solution to obtain water cut95%once more.The injection rate was0.3mL/min in flooding process.The oil recovery was determined as the following equation:EOR=E−E W(1)48S.Gou et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 471(2015)45–53Table 1The characteristics of PAAD.SampleaFeed ratio (wt%)Intrinsic viscosityViscosity-average molecular weightAMAADBDAPPAAD59.939.90.2772.12mL/g3.26×106aThe intrinsic viscosity and viscosity-average molecular weight were determined according to Refs.[28,29].where E is the total oil recovery ratio,E W is the oil recovery of water flooding.3.Results and discussion3.1.Characteristics of PAADThe effect of synthesis conditions on copolymerization of AM,AA and DBDAP were investigated,and the intrinsic viscosity and the viscosity-average molecular weight were measured.The results are summarized in Table 1(see Tables S1and S2and Fig.S1for the details in Supporting information).3.2.FTIR and 1H NMR spectra analysisFTIR and 1H NMR spectra of copolymer PAAD are shown in Fig.1,respectively.From the FTIR curve of PAAD,the strong absorp-tion peaks at 3434cm −1and 1651cm −1respectively assign tothe stretching vibration of N H and C O bond in the CONH 2group.A relatively less intense peaks at 1560and 1401cm −1are due to the COO −group [30].The peaks at 1325and 1119cm −1correspond to the stretching vibrations of SO 2.From the 1H NMR spectra of PAAD,the characteristic peaks around 1.54and 2.15ppm assign to the protons of polymer alkyl chains.The chem-ical shifts at 7.68and 6.87ppm are due to the protons of aromatic ring of DBDAP.It can be inferred that the typical structures of monomers have been successfully incorporated into polymer chain.3.3.Critical association concentration of PAADThe ratio of the intensities between the first and the third band intensity in the fluorescence spectrum of pyrene (I 1/I 3)is used to characterize the size of their environment polar-ity.The weaker polarity of the microenvironment around the pyrene molecule leads to the smaller value of I 1/I 3.Fig.2(a)depicts the relationship curve between the values of I 1/I 3and PAAD concentrations.On the curve of I 1/I 3,the value of I 1/I 3abruptly decreases at a concentration of PAAD about 1.5g/L suggesting the transformation of association type from intra-molecular association into intermolecular association.This is also evident from the curve of the viscosity versus concentration shown in Fig.2(b),and this value is defined as the criti-cal association concentration (CAC)at which the intramolecular association begins to transfer into intermolecular association [31].Fig.1.FTIR and 1H NMR spectra of PAAD.I 1 / I 3Concen tration (mg/L )(a)Concentration (mg/L)A p p a r e n t V i s c o s i t y (m P a ·s )(b)Fig.2.(a)Effect of PAAD concentration on I 1/I 3value;(b)effect of PAAD concentration on viscosity.S.Gou et al./Colloids and Surfaces A:Physicochem.Eng.Aspects471(2015)45–5349Fig. 3.Characteristics of different complex solutions(a)PAAD/C6mimBr;(b) PAAD/C8mimBr;(c)PAAD/C10mimBr;(d)PAAD/C12mimBr;(e)PAAD/C14mimBr;(f) PAAD/C16mimBr and(g)PAAD/CTAB.3.4.Characteristics of PAAD/ILs complex solutionsThe complex solutions of polymer PAAD and different ILs were obtained,and the complex of PAAD and CTAB was also pre-pared for comparing.CTAB is one of the most common used cationic surfactants for EOR.The concentration of PAAD wasfixed at3g/L.The photographs in Fig.3(a–g)show the different com-plex solutions,viz.,(a):PAAD/C6mimBr,(b):PAAD/C8mimBr,(c): PAAD/C10mimBr,(d):PAAD/C12mimBr,(e):PAAD/C14mimBr,(f): PAAD/C16mimBr and(g):PAAD/CTAB.However,when the concen-tration of C n mimBr,n=10,12,14and16,and CTAB is as low as 0.3g/L,a gel phase is observed in our experiment.This unexpected result can be owing to the strong binding of ion-pair interaction between cationic head groups and anion polymer corresponding to structural alkyl chain length of ILs.When the concentration of C n mimBr,n=6and8,is above40g/L,the solutions have remained transparent.The air/water critical micelle concentration(cmc)values of C6mimBr and C8mimBr were measured and compared with the values reported in the literatures at303.15K.The obtained cmc values of465mM for C6mimBr and118mM for C8mimBr are in agreement with the reported values470and121mM,respectively [32,33].Therefore the ILs concentrations werefixed at their cmcs in pure water to investigate the effect of ILs on complexes viscosity in the concentration of copolymer from1to5g/L.From Fig.3it is observed that with the concentration of C6mimBr around470mM, the viscosity of PAAD/C6mimBr complex decreases notably,e.g.the viscosity of3g/L PAAD decreases from660.5to8.7mPa s due to the large concentration of C6mimBr similarly to C8mimBr as discussed below.Because of the limitations of low viscosity of PAAD/C6mimBr complex and the high concentration of C6mimBr,studies of the interaction of IL and PAAD are focused on PAAD/C8mimBr complex.3.5.Effect of C8mimBr concentration on viscosityEffect of C8mimBr concentration on viscosity of2g/L and3g/L PAAD solutions is displayed in Fig.4.The concentration spanning a range from below to above the cmc of C8mimBr is actually higher than the39.9wt%anionic acrylic linked in PAAD chains at this mass ratio causing C8mimBr to partly incorporate with the PAAD and partly remain in the solutions which is also indicated in the TG-DSC results discussed below in this paper.Addition of C8mimBr causes an obvious decrease in the viscosity of complex solution due to the ionic C8mimBr reduces the electrostatic repulsion of polymerConcentration of IL (g/L)ApparentViscosity(mPa·s)Fig.4.Effect of C8mimBr concentration on complex viscosity: PAAD:3g/L,᭹PAAD:2g/L.chains,and cationic hydrophobic head groups adsorb on the anionic PAAD by opposite ion charge interaction leading to the polymer coils much more compact.The hydrophobic effect is apparently too strong in this system for the polymer coils to expand[8].3.6.Interfacial tension test3.6.1.Effect of C8mimBr concentration on interfacial tensionThe IFT changes versus PAAD/C8mimBr complex and C8mimBr at different concentrations of C8mimBr are depicted in Fig.5(a).The concentration of PAAD wasfixed at3g/L.The amphiphilic C8mimBr tends to migrate the interface leading to the adsorption,and con-sequently dropping the IFT.The lower values of IFT of C8mimBr are relevant in the presence of hydrophobically associating copolymer PAAD.For instance,the IFT decreases from2.1mN/m corresponding to30g/L C8mimBr to a minimum value of0.77mN/m correspond-ing to30g/L C8mimBr combined with3g/L PAAD.Accordingly,we carried out the study and discuss below on PAAD/C8mimBr with the30g/L C8mimBr.This can be explained by the surface activity of the copolymer and the Na+originated from PAAD copolymer solution.In details,adsorption of copolymer at the surface would necessarily compress the area available for ILs adsorption leading to the increase of surface excess ILs concentration and causing a lowering of the interface tension[8].In addition,Na+has higher surface charge density.The stronger hydration will be,the smaller number of water molecules available to hydrate[C8mim]+as a result of salting out effect[34].To further increase the concentra-tion of C8mimBr in PAAD solution,the higher surface tension of PAAD/C8mimBr complex demonstrates binding of ILs to the copoly-mer and concomitant depletion of ILs from the interface.3.6.2.Effect of polymer concentration on interfacial tensionAs presented in Fig.5(b),the effect of PAAD concentration from 1to5g/L on IFT of PAAD/C8mimBr complex and crude oil is inves-tigated.The results demonstrate a higher concentration above the CAC of PAAD did not modify the IFT significantly.The changes of concentration of polymer have no obvious effect on IFT of system due to C8mimBr forms mixed micelle with hydrophobic groups attached to the polymer.The concentration of PAAD/C8mimBr com-plex in the following research is3g/L PAAD with30g/L C8mimBr unless noted.3.6.3.Effect of temperature on interfacial tensionIn this stage,the effect of temperature(303K,308K,313K, 323K,333K and338K)on the IFT of PAAD/C8mimBr solution and50S.Gou et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 471(2015)45–53I n t e r f a c i a l T e n s i o n (m N /m )Concentration of C 8mimBr (g/L)(a)I n t e r f a c i a l T e n s i o n(m N /m )Concentration of PAAD (g/L)(b)I n t e r f a c i a l T e n s i o n (m N /m )Temperure (oC)(c)I n t e r f a c i a l T e n s i o n (m N /m )Concentration of NaCl (g/L)(d)Fig.5.(a)Effect of C 8mimBr concentration on IFT;(b)effect of PAAD concentration on IFT;(c)effect of temperature on interfacial tension;(d)effect of NaCl concentration on interfacial tension: C 8mimBr:3wt%,᭹C 8mimBr:1wt%, C 8mimBr:0.5wt%, C 8mimBr:0.2wt%.crude oil was studied,and the effect of temperature on the IFT of C 8mimBr and crude oil was also investigated.The obtained results are given in Fig.5(c).The increasing temperature leads to the increase of IFT between C 8mimBr solutions and crude oil.This is because of the presence of nitrogen atoms with sp2hybridization in and the positive charge is in resonance,thus the diffusion of ILs into the oil phase increases as temperature increases leading to emulsion inversion from oil-in-water to water-in-oil resulting in the increase of IFT [20].However,the results reveal that with the temperature increase the IFT of PAAD/C 8mimBr solution and crude oil slightly decreases,which may be due to the hydrophobic asso-ciation of PAAD enhances as the temperature increases within a certain scope leading to lower IFT values.3.6.4.Effect of NaCl concentration on interfacial tensionThe effect of NaCl concentration on the IFT of PAAD/C 8mimBr solution and crude oil with different concentrations of C 8mimBr was examined.The results given in Fig.5(d)revealed that the IFT reduced at higher NaCl concentrations due to the enhancement of hydrophobic association of complex and the salting out effect discussed earlier in this paper.For instance,the complex of 3g/L PAAD and 5g/L C 8mimBr with 20g/L NaCl can reduce the IFT to 0.85mM/m.In a word,with electrolytes,the interaction param-eter tends to higher positive values indicating reduction in the repulsive interactions between cationic head group of IL molecules [34].This observed trend makes the PAAD/C 8mimBr complex aseffective alternative for EOR processes dealing with harsh salinity conditions.3.7.Effect of temperature and shear rate on viscosityThe effect of temperature on the apparent viscosity of PAAD (2g/L)and PAAD/C 8mimBr complex solutions at a shear rate of 170s −1is shown in Fig.6(a).The viscosity of PAAD decreases then increases followed by a decrease,and it attains a maximum value at 90◦C.This may be due to that the high temperature can enhance hydrophobic association of PAAD.However,to further increase the temperature,the hydrophobic groups are disrupted,so that the viscosity decreased.The viscosity of PAAD/C 8mimBr complex maintains slight decrease from 22.2to 17.4mPa s with temperature raising from 30to 90◦C showing excellent temperature resistance.This decrease may be due to the more enhancing hydrophobic effect with the increasing temperature in this system limiting the poly-mer coils to expand.The shear thinning behavior of PAAD (2g/L)and PAAD/C 8mimBr complex solutions was measured,and the results are shown in Fig.6(b).The shear thinning behavior and reversible are important for polymer injection.At high shear rate,the apparent viscosity of PAAD and PAAD/C 8mimBr complex solutions exhibits a significant decrease.To research the recoverability to alteration in the shear rate,the sample solutions maintained shearing at 170s −1for 5min,next kept shearing at 500s −1for 5min,then went on shearing atS.Gou et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 471(2015)45–535110100A p p a r e n t V i s c o s i t y (m P a ·s )Temperature (oC)(a)Shear Rate (s-1)A p p a r e n t V i s c o s i t y (m P a ·s )(b)Shear Rate (s -1)A p p a r e n t V i s c o s i t y (m P a ·s )Time (s)(c)100200300400500Shear Rate (s -1)A p p a r e n t V i s c o s i t y (m P a ·s )Time (s)(d)100200300400500Fig.6.(a)Effect of temperature on viscosity;(b)effect of shear rate on viscosity;(c)recovering ability of PAAD for shear rate;(d)recovering ability of PAAD/C 8mimBr for shear rate.170s −1for 5min.The results are shown in Fig.6(c,d).When shear rate suddenly changes from 170to 500s −1,the viscosity of PAAD and PAAD/C 8mimBr drops sharply,and when shear rate decreases from 500to 170s −1,the viscosity of PAAD and PAAD/C 8mimBr com-plex recovers immediately.About 87.6%viscosity retention rate compared with the original viscosity is obtained by PAAD,and for PAAD/C 8mimBr complex,the viscosity is equal to the original vis-cosity.It has been shown that the interaction between PAAD and C 8mimBr has excellent recovering ability for shear rate.3.8.TG and DSCTG and DSC were used to analyze the thermal decomposition of PAAD and PAAD/C 8mimBr complex.The results are presented in Fig.7(a,b).As shown in TG diagram of PAAD,the thermogravi-metric stage occurs with the mass loss of 77.96wt%which could be attributed to the decompositions and carbonization of copoly-mer.The TG diagram of PAAD/C 8mimBr displays two stages for the weight loss.The first step occurs in the range of 40–450◦CW e i g h (%)Temperture (oC)(a)D S C (m W /m g )Temperture (oC)(b)Fig.7.(a)TG diagram of PAAD and PAAD/C 8mimBr;(b)DSC diagram of PAAD and PAAD/C 8mimBr.。

w ww .s p m .c om .c n第28卷　第6期2007年6月纺　织　学　报Journal of T extile Research V ol.28　N o.6Jun.　2007文章编号:025329721(2007)0620092204聚苯乙烯丙烯酸丁酯表面改性的超细颜料性质孟庆豪,房宽峻,付少海(江南大学生态纺织教育部重点实验室,江苏无锡　214122)摘　要　为提高涂料印花中织物摩擦牢度,减少黏合剂等助剂的使用,以苯乙烯、丙烯酸丁酯为单体用微乳液聚合法对颜料蓝15∶1进行表面包覆改性,探讨了表面活性剂用量、单体用量等对所制备的超细颜料平均粒径、粒径分布和分散稳定性的影响,用扫描探针显微镜观察了改性颜料的形貌。

结果表明:随着单体用量的增加,颜料的平均粒径先增大后减少;颜料分散时表面活性剂的用量影响体系的分散稳定性及颜料的平均粒径;表面改性后的超细颜料在无黏合剂存在的情况下,对纯棉织物的摩擦牢度有一定的改善。

关键词　聚苯乙烯丙烯酸丁酯;微乳液聚合;超细颜料;性质中图分类号:TS194.21 文献标识码:A Properties of nanoscale pigment surface 2modified bypolystyrene 2butyl acrylateME NG Qinghao ,FANG K uanjun ,FU Shaohai(K ey Laboratory o f Science and Technology o f Eco 2Textile ,Ministry o f Education ,Southern Yangtze Univer sity ,Wuxi ,Jiangsu 214122,China )Abstract C.I.Pigment Blue 15∶1was encapsuled by miniemulsion polymerization with styrene and butyl acrylate for the purpose of im proving the rubbing fastness and reducing the use of auxiliaries such as binders.The effects of the am ount of surfactants and m onomers on the average particle sizes ,PDI ,stability of the system were investigated.The m orphologies of the ultrafine particles were observed by the scanning probe microscope.The results indicated that the average particle size of the pigment first increases and then decreases as the am ount of the m onomers increases ;the am ount of surfactant affects the average particle sizes and the stability of the system ;the rubbing fastnesses of the m odified pigment for pure cotton fabric is rather g ood with absence of binders.K ey w ords polystyrene 2butyl acrylate ;miniemulsion polymerization ;ultrafine pigment ;property收稿日期:2006-09-17 修回日期:2006-12-26作者简介:孟庆豪(1983—),男,硕士生。

Colloids and Surfaces A:Physicochem.Eng.Aspects 361 (2010) 180–186Contents lists available at ScienceDirectColloids and Surfaces A:Physicochemical andEngineeringAspectsj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c o l s u r faSynthesis and characterization of a functionalized graft copolymer of densified cellulose for the extraction of uranium(VI)from aqueous solutionsT.S.Anirudhan ∗,S.S.SreekumariDepartment of Chemistry,University of Kerala,Kariavattom,Trivandrum 695581,Kerala,Indiaa r t i c l e i n f o Article history:Received 29September 2009Received in revised form 21February 2010Accepted 21March 2010Available online 27 March 2010Keywords:Graft copolymers Densified cellulose Uranium(VI)Adsorption isotherm Desorptiona b s t r a c tA novel carboxylate functionalized graft copolymer (PGTDC-COOH)based on TiO 2-densified cel-lulose (TDC)was prepared by grafting poly(methacrylic acid)onto TDC in the presence of N,N -methylenebisacrylamide (MBA)as a cross-linking agent and Mn(IV)–citric acid as an initiator sys-tem.Adsorbent was characterized using FTIR,SEM,XRD,TG-DTG,BET-N 2adsorption measurements,Boehm and potentiometric titrations.The adsorption efficiency of PGTDC-COOH for uranium(VI)from aqueous solutions was examined by batch experiments.The optimum pH was found to be 6.0.Kinetic studies show that the uptake was rapid and equilibrium was established in 1h.The sorption process fol-lows the pseudo-second-order kinetic ngmuir analysis showed that the surface of the adsorbent is uniform and homogeneous in respect to sorption and energy.The adsorption equilibrium constant and maximum adsorption capacity were evaluated to be 0.074L/mg and 99.4mg/g,respectively.Utility of the adsorbent was tested by removing U(VI)from simulated nuclear industry wastewater.The possibility of metal recovery from spent adsorbent was investigated using HCl solutions with different concentrations and greater than 96.0%recovery was achieved with 0.1M HCl.© 2010 Elsevier B.V. All rights reserved.1.IntroductionAdsorption of metal ions from a solution to an adsorbent is con-trolled by the surface functional groups of the adsorbent.Cellulosic fibers generally have very few functional groups that are capable of adsorbing metals.Sorption properties can be improved by grafting new functional groups onto the cellulose backbone.Many differ-ent kinds of functionalities have been studied for their potential to remove metal ions from aqueous solutions such as iminoacetic acid [1],Schiff bases [2],amidoxime [3],amine [4],thiosemicar-bazide [5],carboxylic acid [6],phosphoric acid [7]and sulphonic acid [8]groups.In particular,carboxylic acid functional group is important because of the high potential of the carboxylate function-ality for the removal of heavy metal ions from aqueous solutions [9].Cellulose has two distinct regions,the crystalline zone and the amorphous zone [10].Chemical reactions generally do not take place on the crystalline region of cellulose.On the other hand,embedding TiO 2on cellulose should affect the crystalline struc-ture making it more suitable for activation reaction [11].Earlier workers have demonstrated that by using the TiO 2-densified cellu-lose for the preparation of the adsorbent,it is possible to take the advantage of high porosity,hydrophilicity,chemical modifiability,regular spherical shape,particle size,high density and mechani-∗Corresponding author.Tel.:+914712418782.E-mail address:tsani@ (T.S.Anirudhan).cal strength [11].The sorption of metal ions can be enhanced by grafting functional groups onto cellulose-based matrix.The recovery of uranium(VI)from resources such as sea water,industrial wastewater,industrial phosphoric acid and other waste sources is of great concern,due to the increasing needs of this metal for the production of electricity as well as the expected shortage of this metal in the near future.The limited world reserves and their location in developing countries have led to the development of new techniques for the removal and recov-ery of U(VI),particularly from waste streams of nuclear industries.Adsorption is one of the methods commonly used to remove U(VI)ions from aqueous medium with relatively low metal ion concentrations.This work aims at preparing a new carboxylate functionalized graft copolymer through graft polymerization reac-tion of poly(methacrylic acid)onto TiO 2-densified cellulose in the presence of N,N -methylenebisacrylamide (MBA)as a cross-linker and Mn(IV)/citric acid as an initiator system for the effective removal of U(VI)from aqueous solutions.The adsorption of U(VI)was studied in batch system with respect to the initial pH,contact time,initial concentration,ionic strength,and adsorbent dose.2.Experiment 2.1.MaterialsHigh purity cellulose used for the preparation of cellulose xanthate was purchased from Fluka,Switzerland.All chemicals0927-7757/$–see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.colsurfa.2010.03.031T.S.Anirudhan,S.S.Sreekumari/Colloids and Surfaces A:Physicochem.Eng.Aspects361 (2010) 180–186181Scheme1.Preparation of PGTDC-COOH.were analytical grade.U(VI)stock solution was prepared by using UO2(NO3)2·6H2O(Fluka).Methacrylic acid(MA)and MBA from Fluka,Switzerland,were used for graft copolymerization.Titanium dioxide(rutile)obtained from Travancore Titanium Products Ltd. India,was used for densification of cellulose.The chemicals such as KMnO4,CS2,and citric acid were of analytical grade supplied by E. Merck,India Ltd.2.2.Preparation of adsorbentCellulose xanthate viscose wasfirst prepared by reacting20g of alkali treated cellulose with10mL CS2and then dissolving in 6%NaOH solution.Titanium dioxide densified cellulose(TDC)was prepared by the method described by Lei et al.[11].For this,rutile and viscose(containing8.0%cellulose)in the weight ratio1.5:10 were dispersed in a solution of200mL chlorobenzene and100mL pump oil in1Lflask.The suspension was agitated with a speed of 300rpm at90◦C for1h.The resulting particles werefiltered and washed successively with benzene and methanol.The decomposi-tion of cellulose xanthate was completed by immersing particles in a solution of acetic acid and ethanol in the ratio1:2.The TDC thus obtained was washed with water,dried at60◦C and then sieved to −80+230mesh size of particles correspond to an average diameter of0.096mm.Scheme1represents the general procedure adopted for the preparation of poly(methacrylic acid)grafted TDC(PGTDC-COOH) bearing–COOH functional group.Graft polymerization of MA onto TDC was carried out in water using MnO2/citric acid redox system[12].About10g of TDC was immersed in500mL of0.1N aqueous KMnO4solution (solid–liquid ratio1:50)and shaken for30min at room temper-ature to ensure uniform deposition of MnO2all over the sample surface.After impregnation,the sample was washed repeatedly with distilled water and squeezed betweenfilter papers.For graft polymerization,the sample-to-liquid ratio1:50was used.The permanganate-treated sample was immersed in a solution contain-ing citric acid(0.4mequiv./L g of TDC).Methacrylic acid(0.5mL/1g of TDC)and MBA(0.1g)were then added with constant stirring under the controlled supply of N2.The contents were heated at 60◦C for1h.The product PGTDC-COOH was washed with methanol and dried at60◦C and then stored in a desiccator until use.The graft yield was calculated by the following equation:Graft yield(%)=w−w0×100(1)where w is the weight of grafted TDC sample and w0is the weight of TDC.Grafting yield was found to be51.57%.2.3.Equipments and methods of characterizationCharacterization of the graft copolymer was compared with the native cellulose.FTIR spectra of the PGTDC-COOH and cellu-lose were recorded on a KBr disk using a Perkin Elmer IR180 spectrophotometer.X-ray diffraction(XRD)analyses were car-ried out with a Rigakku diffractometer using Cu K␣radiation. In order to study the morphological changes during modifica-tion,the samples before and after modification were observed under a Scanning Electron Microscope(SEM)model S-2400Hitachi. Thermal stability of the adsorbents was studied with a Metler Toledo Star thermogravimetric analyzer.The surface area was measured by the BET method using a model Q7/S surface area analyzer(Quantasorb,USA).A potentiometric method[13]was used to determine the pH of point of zero charge(pH pzc).The carboxyl content of PGTDC-COOH was determined by neutral-ization of carboxyl groups of the adsorbent with0.1M NaHCO3 solution using a titration method described by Boehm[14].The cation exchange capacity(CEC)of the adsorbent was determined by NaNO3saturation method using a column operation.The pH and density measurements were made using a pH meter(model ␮-362,Systronics,India)and a specific gravity bottle,respec-tively.A temperature controlled water bath shaker(Labline,India) with temperature variation of±1◦C was used for the equilibrium studies.The concentration of U(VI)in solution was determined using GBC Avanta A5450atomic absorption spectrophotometer (AAS).2.4.Adsorption experimentsThe adsorption of U(VI)from aqueous solutions onto PGTDC-COOH was investigated through batch experiments.A weighed amount of adsorbent(0.1g)was placed in a100mL Erlenmeyer flask containing50mL U(VI)solution.The initial pH of the solution was adjusted to the desired value by adding0.1M HNO3or NaOH. The contents were shaken at200rpm at desired temperature for a predetermined period of time using water bath shaker and then were centrifuged.The concentration of U(VI)in the supernatant was measured using AAS.The adsorption capacity was calculated using the following mass balance equation:q e=(C0−C e)VW(2) where q e is the equilibrium adsorption capacity(mg/g),C0and C e are the initial and equilibrium concentrations of U(VI)in solution (mg/L),respectively.V is the liquid phase volume(L)and W is the amount of the adsorbent(g).Kinetic studies were conducted using four different initial con-centrations(25,50,75and100mg/L)of U(VI)at30◦C.Samples were withdrawn at regular intervals to plot the amount adsorbed versus time.The effects of contact time(0–120min),solution pH (2–8)and adsorbent dose(0.5–5.0g/L)on U(VI)adsorption were studied.The isotherm experiments were performed at30◦C using different concentrations of U(VI)in the range25–500mg/L at pH 6.0.2.5.Desorption studiesDesorption studies were carried out with varying concen-trations of HCl solutions.The sorbent recovered following the adsorption of10mg/L of U(VI)solution was agitated with50mL HCl solution.The sorbent was then removed by centrifugation. The desorbed uranium in the aqueous solution was estimated as previously.182T.S.Anirudhan,S.S.Sreekumari/Colloids and Surfaces A:Physicochem.Eng.Aspects361 (2010) 180–186Fig.1.FTIR spectra of cellulose,PGTDC-COOH and U(V1)adsorbed PGTDC-COOH.3.Results and discussionThe PGTDC-COOH adsorbent was obtained through the grafting of MA onto TDC using MBA as cross-linker and Mn(IV)/citric acid as initiator.TiO2is embedded in the cellulose skeleton to form a composite matrix.The particles not only increased the density of the composite matrix but also act as a loosefiller to facilitate the activation.The initiator system abstracts hydrogen from the methyl hydroxyl groups of the cellulose to form active sites on the TDC backbone.These active sites interact with monomer to form graft copolymer.Since a cross-linking agent(MBA)present in the system, a polymer network is formed with free–COOH groups at the chain end.The adsorbent was found to be stable in mineral acids and alkalies.3.1.Adsorbent characterizationThe FTIR spectra of cellulose,PGTDC-COOH and the U(VI) adsorbed PGTDC-COOH are shown in Fig.1.Cellulose exhibits a broad absorption band at3344cm−1characteristic of–OH group and a sharp peak at2900cm−1characteristic of C–H stretching from–CH2group.Appearance of an absorption band at1160cm−1 is attributed to the1–4glycosidic linkage of cellulose[15].The IR spectrum of PGTDC-COOH exhibits a broad signal around 3417cm−1representing the overlap of O–H,C–H,N–H and C–O stretching vibrations[16].The peaks at1638and1510cm−1show the presence of amide carbonyl group and aliphatic amide group, respectively,due to cross-linking.These observations indicate the presence of a polymeric chain in PGTDC-COOH.The sharp bands at1690cm−1( C O)and1450cm−1( C–O)show the presence of–COOH group[17].The presence of these adsorption bands in the IR spectrum of the PGTDC-COOH confirms that MA has been successfully grafted on the cellulose backbone.The C–O stretch-ing vibration of–C–OH group in cellulose at1059cm−1shifts to 1021cm−1in PGTDC-COOH due to grafting.In PGTDC-COOH the peak at721cm−1can be attributed to symmetric O–Ti–O stretch-ing and the peak around632cm−1is indicative of the stretching vibration of Ti–O[18].The adsorption of U(VI)onto PGTDC-COOH caused the shifting of certain peaks in PGTDC-COOH and appear-ance of certain characteristic peaks.The bands at3417,1690, 1450and1021cm−1in PGTDC-COOH were shifted to3430,1705,Fig.2.TG and DTG curves of cellulose and PGTDC-COOH.1468and1034cm−1,respectively in the spectrum of U(VI)loaded PGTDC-COOH.The appearance of a peak at930cm−1U(VI)loaded PGTDC-COOH is characteristic of O U O stretching vibration[19]. Literature suggests that in the modification of synthetic and natu-ral polymers by grafting,the grafted polymer chains are covalently linked and inter positioned on the cellulosic backbone polymer [20].The increase in weight of the graft polymer,compared to the original weight of TDC,showed that grafting had occurred.The car-boxylic acid group content in the adsorbent and CEC are also in conformity with the grafting of MA onto cellulose backbone.The thermal degradation of cellulose and PGTDC-COOH has been monitored from ambient to800◦C.The comparative thermal decomposition processes occurring in cellulose and the adsorbent were carried out by TG and DTG analyses and are shown in Fig.2. The thermal decomposition of cellulose occurred in two degrada-tion steps:(1)240–360◦C and(2)360–540◦C.In thefirst stage of decomposition(T1=344◦C)almost49.5%is lost due to pyrolysis, and in the second stage(T2=514◦C)92.6%of the initial dry weight is due to carbonization.The TG and DTG curves of the adsorbent indi-cate two stage decomposition between280and400◦C(T1=306◦C) where51.1%loss was observed due to the pyrolytic depolymeriza-tion process.The second stage decomposition between400and 560◦C(T2=540◦C)where71.6%of initial dry weight loss was observed leaving behind TiO2residue and char.The initial decom-position temperature(280◦C)and the temperature at50%weight loss(380◦C)of the grafted polymer were higher than those of the ungrafted cellulose(240and360◦C,respectively).The results indi-cate that grafting poly(methacrylic acid)onto cellulose results in an increase in thermal stability.SEM photographs of the cellulose and PGTDC-COOH are shown in Fig.3.The cellulosefibers exhibit distinctflake and are lump-ish because of the strong intra-molecular hydrogen bonds[21]. The PGTDC-COOH possesses a porous structure due to the incor-poration of polymer chains which hampered the formation of intra-molecular hydrogen bonds.Such a porous structure should significantly increase the available surface area of the adsorbent and therefore,increase the adsorption capacity.The grafted side chain through covalent bonding of methacrylic acid seems to form a heterogeneous surface in the graft copolymer showing proof of grafting.The XRD patterns of the cellulose,PGTDC-COOH and U(VI)-adsorbed PGTDC-COOH are shown in Fig.4.Curve(a)reports peaks at16.5◦,22.6◦and33.9◦which constitute the partial crystallineT.S.Anirudhan,S.S.Sreekumari/Colloids and Surfaces A:Physicochem.Eng.Aspects361 (2010) 180–186183Fig.3.Scanning electron micrographs of cellulose and PGTDC-COOH. nature of cellulose like all natural polymers[22].This indicates that cellulose molecules are arranged in ordered lattice in which –OH groups are bonded by strong secondary forces.The diffraction peaks of PGTDC-COOH suggested it to be more crystalline related to the presence of TiO2as denser material for modification.The major peak appeared at2Â=27.5◦corresponds to the presence of rutile [23].It can be seen from the curves(b)and(c)that U(VI)loaded PGTDC-COOH retains the XRD patterns of PGTDC-COOH even after loading,with increasing intensity of the peaks at2Â=36.1◦,44.6◦and54.4◦[24].The surface charge density( 0)of the cellulose and PGTDC-COOH was determined by batch potentiometer titration procedure.For titration experiments0.1g of adsorbent was added to50mLFig.4.XRD patterns of cellulose,PGTDC-COOH and U(V1)adsorbedPGTDC-COOH.Fig.5.Surface charge density of cellulose and PGTDC-COOH as a function of pH inaqueous solution of NaNO3.of0.1M NaNO3.The pH of the solutions were carefully adjustedbetween2and8with0.1M HNO3and NaOH solutions,and thensuspensions were shaken in a water bathflask shaker at200rpmfor6h.Find out the volumes of alkali and acid required to changethe pH.The values of 0can be calculated using the equation:0=F(C A−C B)+([OH−]−[H+])A(3) where F is the Faraday constant(96485C/g equiv.),C A and C B are theconcentrations of strong acid and base after each addition duringtitration(equiv./L),and[H+]and[OH−]are the equilibrium concen-trations of H+and OH−ions,respectively,bound to the suspensionsurface(equiv./cm2).A plot of 0versus pH is given in Fig.5.Thepoint of intersection of 0with the pH curves gives the pH pzc of5.0and5.6for cellulose and the adsorbent,respectively.The cationexchange capacity(CEC)of cellulose and PGTDC-COOH was foundto be0.69and1.50mequiv./g,respectively.The carboxylic acidgroup content in PGTDC-COOH was found to be1.88mequiv./g.Thespecific surface area of cellulose and PGTDC-COOH measured by theN2adsorption was29.8and55.1m2/g,respectively.The density ofcellulose and PGTDC-COOH was found to be0.82and1.85g/mL,respectively.3.2.Adsorbent dose on U(VI)adsorptionThe adsorption of U(VI)by cellulose and PGTDC-COOH from U(VI)solution at different adsorbent doses(0.5–5.0g/L)was inves-tigated.The results are shown in Fig.6.Increase in the adsorbentdosage increased the percent removal of U(VI),which is due to theincrease in the surface area of the adsorbent.The complete removalof U(VI)ions from solution containing10mg/L U(VI)was achievedby4and2g/L of cellulose and PGTDC-COOH,respectively.The dataclearly indicate that PGTDC-COOH is two times more effectivethanFig.6.Effect of adsorbent dose on the adsorption of U(VI)onto cellulose and PGTDC-COOH.184T.S.Anirudhan,S.S.Sreekumari/Colloids and Surfaces A:Physicochem.Eng.Aspects361 (2010) 180–186Fig.7.Effect of pH on the adsorption of U(VI)onto PGTDC-COOH. cellulose for the removal of U(VI)from aqueous solution.The high adsorption capacity was probably due to the presence of–COOH groups formed after modification.3.3.Effect of pH on U(VI)removalThe pH of the aqueous solution affects the surface charge of the adsorbents as well as the degree of ionization and speciation of the solute.The adsorption of U(VI)on PGTDC-COOH was studied varying the solution pH from2to8.The percentage of adsorption increases with increasing pH value,reaches a maximum at pH6.0 and then remains almost constant(Fig.7).For an initial concen-tration of10and25mg/L,the amount adsorbed was found to be 4.99mg/g(99.9%)and12.12mg/g(97.0%),respectively,at pH6.0. Experimental results show that thefinal pH of the solution after adsorption was about4.7when the initial concentration of U(VI) was25mg/L and the original pH was6.0.This also indicates that H+ions are released by exchange mechanism with the removal of U(VI).At low pH,the H+competition with uranium binding sites limits the uptake efficiency.At lower pH values the predomi-nant species is UO22+.As the solution pH increases,the uranium speciation in the solution changes and the hydrolysis products such as UO2(OH)+,UO2(OH)22+and(UO2)3(OH)5+are formed[25]. In weakly acidic solution,i.e.,in the range5.0–6.0the dominant species are UO2(OH)+ions which are formed by the hydrolysis of UO22+ions[26].Hence in the pH range,ion exchange followed by complexation is the major mechanism.mPGTDC-COOH+M n+→(PGTDC-COO)m M+n H+(4) where M n+=UO22+and UO2(OH)+.The complex formation was con-firmed by the peak at930cm−1in the IR spectrum of U(VI)adsorbed PGTDC-COOH which is characteristic of O U O stretching vibra-tion.The pH pzc for PGTDC-COOH was found to be5.6and hence at pH6.0the surface of PGTDC-COOH is slightly negatively charged and the positively charged U(VI)ions are adsorbed on the surface by electrostatic attraction.The variation of surface charge density of PGTDC-COOH with pH and the formation of the hydroxo species reveal that U(VI)ions are adsorbed on PGTDC-COOH by both ion exchange and complexation mechanism.3.4.Effect of contact time and initial concentrationFig.8shows the effect of contact time on the adsorption of U(VI) onto PGTDC-COOH at different initial concentrations.The removal rate of U(VI)was rapid during thefirst10min,then increased slowly with the time extension and leveled off at1h.The initial con-centration did not have a significant effect on the time to reach equilibrium.The rapid kinetics has significant practicalimportance,Fig.8.Effect of contact time and initial concentration on the adsorption of U(VI)onto PGTDC-COOH and comparison of observed data with pseudo-second-order kinetic model.as it facilitates smaller reactor volumes,ensuring high efficiency and economy[27].The time profile of U(VI)uptake is a single, smooth and continuous curve leading to saturation suggesting the monolayer coverage of U(VI)on the surface of the adsorbent.The equilibrium adsorption capacity(q e)was12.12,23.17,32.10and 41.20mg/g,respectively,at an initial concentration of25,50,75 and100mg/L,respectively at30◦C.It is evident that the amount of metal ion adsorbed increases with increasing U(VI)concentra-tion.This is due to the increase in the mass driving force which accelerates the diffusion of U(VI)molecules from bulk solution to the adsorbent surface.Thus the initial U(VI)concentration plays an important role in determining the maximum uptake capacity of the PGTDC-COOH for U(VI).3.5.Effect of ionic strengthThe effect of ionic strength on the removal of U(VI)ions from solution was investigated with varying concentrations of NaNO3. The adsorption capacity with NaNO3concentration of0.001,0.005, 0.01,0.05,0.1and0.5M was found to be90.3,87.6,83.3,78.1, 75.6and60.3%,respectively,at an initial U(VI)concentration of 50mg/L.The adsorption decreases with the increase in solution ionic strength.The adverse effect of ionic strength suggests the pos-sibility of ion exchange mechanism in the adsorption of U(VI)ions onto PGTDC-COOH.Adsorption is sensitive to change in the concen-tration of the supporting electrolyte if the electrostatic interaction is very significant[28].The reduction in the metal removal percent-age may be due to the presence of Na+ions which can compete with U(VI)ions for the same cation exchange sites of PGTDC-COOH. 3.6.Adsorption kineticsKinetics of adsorption is one of the most attractive character-istics to be responsible for the efficiency of adsorption.Since the major mechanism involved in the removal of U(VI)by PGTDC-COOH may be ion exchange followed by complexation,the kinetic data were modeled using pseudo-second-order kinetic model[29].The pseudo-second order rate expression is given bytq t=1k2q e2+tq e(5) where q e and q t are the amount of solute adsorbed per unit adsorbent at equilibrium and time t,respectively.k2is the rate constant for the pseudo-second-order kinetics.The kinetic param-eters estimated are listed in Table1.The value of k2decreases from 4.68×10−2to1.67×10−2g/mg min with an increase in the initialT.S.Anirudhan,S.S.Sreekumari /Colloids and Surfaces A:Physicochem.Eng.Aspects 361 (2010) 180–186185Table 1Kinetic parameters for the adsorption of U(VI)onto PGTDC-COOH.Concentration (mg/L)k 2(g/mg min)q e ,exp (mg/g)q e ,cal (mg/g)R 225 4.68×10−212.1212.320.99950 2.89×10−223.1723.500.99975 1.83×10−232.1332.570.9991001.18×10−241.2041.890.999concentration from 25to 100mg/L.The decrease in the k 2val-ues with increasing concentration might be due to a progressive decrease in covalent interactions,relative to electrostatic interac-tions,of the sites with lower affinity for U(VI)that occurs with increasing initial U(VI)concentration.The correlation coefficient,R 2values (>0.99)for different initial concentrations indicate that the adsorption system belongs to the pseudo-second-order model.Fig.8shows that the theoretical q t values are very close to the experimental values.It is also found that the calculated adsorp-tion amount at equilibrium (q e ,cal )agrees reasonably well with the experimental data in the pseudo-second-order model.Therefore the pseudo-second-order model is suitable to describe the kinetic data.The mechanism involved in the adsorption of U(VI)onto PGTDC-COOH is confirmed as ion exchange followed by complex-ation.For the pseudo-second-order reaction the rate limiting step may be chemisorption,which may involve valency forces through sharing or exchange of electrons between adsorbate and adsorbent.3.7.Adsorption isothermThe analysis of the isotherm data is important to develop an equation which accurately represents the results and could be used for designing purposes.The equilibrium sorption was measured in batch experiments at 30◦C using different initial concentrations varying from 25to 500mg/L at pH 6.0.The sorption isotherm is shown in Fig.9.The shape of isotherm curves corresponded to a L-type curve,according to Giles classification [30].In this classifica-tion,type-L assumes a monolayer coverage on the active sites of the surface of the adsorbent and all the adsorption sites are supposed to be equivalent.Hence the adsorption data have been subjected to the Langmuirmodel given by the equation:a e =Q 0bC e1+bC e(6)whereQ 0and b are the Langmuir constants related to maximum adsorption capacity and equilibrium constant or energy of adsorp-tion,respectively.q e is the observed adsorption capacity (mg/g)and C e the equilibrium concentration (mg/L).parison of model fit of the Langmuir model to the experimental data for the adsorption of U(VI)onto PGTDC-COOH.The values of Q 0and b were calculated using non-linear regres-sion analysis and were found to be 99.84mg/g and 0.074L/mg,respectively.Since the correlation coefficient (R 2)value for U(VI)in the present study was 0.987,the experimental data may be regarded to reasonably fit the Langmuir model.The theoretical q e values as calculated from the Langmuir model agree perfectly with the experimental q e values (Fig.9).The applicability of the Langmuir isotherm suggests that the surface of the adsorbent is uniform and homogeneous in respect to sorption and energy,and the adsorption process results in the formation of a monolayer coverage of U(VI).Formation of a monolayer on the adsorbent surface further indi-cates the chemical nature of the adsorption,i.e.,chemisorption.The Q 0values for the adsorption of U(VI)on diatomite [31],natural sepi-olite [32],bacteriogenic iron oxides [33],o-phenylene dioxyacetic acid impregnated amberlite XAD resin [34]and amberlite XAD-4functionalized with succinic acid [35]were reported to be 41.17,34.61,9.25,28.79and 12.30mg/g,respectively.The comparison of Q 0value of PGTDC-COOH used in the present study (99.84mg/g)with those obtained in the literature shows that PGTDC-COOH is more effective for the adsorption process.3.8.Test with simulated nuclear industry wastewaterThe suitability of the adsorbent for the removal of U(VI)from nuclear industry wastewater was tested by treating it with simu-lated wastewater containing U(VI)ions [36].The sample contained metal ions based on cations such as U(VI)(10mg/L),Ca 2+(10mg/L),Mg 2+(10mg/L)as well as anions such as Cl −(20mg/L),SO 42−(80mg/L),NO 3−(40mg/L),PO 43−(20mg/L),oxalate (60mg/L)and detergents (20mg/L).The effect of adsorbent dose on U(VI)removal from wastewater was investigated (Fig.10).The removal of U(VI)increases with increase in the adsorbent dosage due to the avail-ability of more adsorption sites.Almost complete (≈100%)removal from 1L sample was possible with 2.5g/L of PGTDC-COOH.The amount of adsorbent used in this study (2.5g/L)was slightly higher than that obtained in the earlier (Section 3.3)batch experiments (2.0g/L)may be due to the presence of other cations (Ca 2+andMg 2+)in wastewater which can compete with U(VI)ions for the same binding sites of the adsorbent.3.9.Desorption studiesAs illustrated in Fig.7low adsorption was found in the low pH range,which implies that the U(VI)adsorbed can be desorbed from spent adsorbent by an acid medium.Hence desorption study wasFig.10.Effect of adsorbent dose on the adsorption of U(VI)from a simulated nuclear industry wastewater sample by PGTDC-COOH.。

Colloids and Surfaces A:Physicochem.Eng.Aspects 370 (2010) 28–34Contents lists available at ScienceDirectColloids and Surfaces A:Physicochemical andEngineeringAspectsj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c o l s u r faPreparation of monodispersed polyelectrolyte microcapsules with high encapsulation efficiency by an electrospray techniqueYu Fukui,Tatsuo Maruyama ∗,Yuko Iwamatsu,Akihiro Fujii,Tsutomu Tanaka,Yoshikage Ohmukai,Hideto Matsuyama ∗∗Department of Chemical Science and Engineering,Kobe University,1-1Rokkodai,Nada-ku,Kobe 657-8501,Japana r t i c l e i n f o Article history:Received 29May 2010Received in revised form 11August 2010Accepted 14August 2010Available online 21 August 2010Keywords:Electrospray Microcapsule PolyelectrolyteHigh encapsulation efficiencya b s t r a c tThe preparation of polyelectrolyte microcapsules by electrospray was investigated.When a polyanionic or polycationic aqueous solution was electrosprayed into an aqueous solution containing a polyelectrolyte with the opposite charge,a spherical interface consisting of a polyelectrolyte complex was formed by electrostatic interaction to produce a microcapsule.Alginate/chitosan microcapsules (∼100␮m)were successfully produced with a narrow diameter distribution (coefficient of variation 4.4%).The diameters of microcapsules were controlled in the range of 80–230␮m by varying the operating conditions,such as feed rate,working voltage,the distance from needle-to-collector,needle diameter and polyelectrolyte concentrations.We also succeeded in the encapsulation of protein,dextran and a polymeric microsphere within the polyelectrolyte microcapsules with high encapsulation efficiencies (more than 99%).The study of yeast encapsulation reveals that the electrospray technique can encapsulate a physiologically active substrate in the polyelectrolyte microcapsule and maintain its activity.© 2010 Elsevier B.V. All rights reserved.1.IntroductionMicroencapsulation has been widely used in the agricultural,food,cosmetics,pharmaceutical and medical industries [1–3].Along with the emerging demand for new functional microcap-sules,the development of a new microencapsulation technique has been a significant target in the research field to achieve effi-cient encapsulation,a biocompatible microcapsule,a functional microcapsule or a controlled-release strategy [4–6].Emulsifica-tion,spray-drying and coacervation techniques are mostly used for encapsulating food ingredients,proteins,drugs,flavors and liv-ing cells.In the last decade,studies in microfluidics technology have provided a novel strategy for the preparation of microcapsules with narrow size-distributions [7–9].The electrospray technique,which is conventionally used as an ionization technique in mass spectroscopy,has a great potential for microcapsule preparation because of the simplicity of the apparatus,its high productivity and its easy setup.Although the electrospray technique can con-tinuously produce tiny droplets or nanofibers with ease,there has been uncertainty around the production of microcapsules.Bugarski et al.first reported microcapsule preparation using the electro-∗Corresponding author.Tel.:+81788036070;fax:+81788036070.∗∗Corresponding author.E-mail addresses:tmarutcm@crystal.kobe-u.ac.jp (T.Maruyama),matuyama@kobe-u.ac.jp (H.Matsuyama).spray technique and demonstrated the effective preparation of size-controlled microcapsules [10].They and other research groups subsequently reported encapsulation of viable living cells using calcium alginate and the electrospray technique [11–14].These reports employed only calcium alginate as a capsule material,prob-ably due to its safety with living cells.In 1980s,relatively large capsules (∼mm)composed of poly-electrolytes were studied to encapsulate cells and enzymes [15,16].These capsules of millimeter size were prepared simply by adding a charged-polyelectrolyte solution dropwise to another oppositely charged-polyelectrolyte solution.In the last decade,the layer-by-layer method using polyelectrolytes have attracted wide attention as a thin film material because they form a stable and insolu-ble complex with an oppositely charged polyelectrolyte [17].In particular,this method can employ synthetic and natural poly-electrolytes and provide a novel class of functional ultrathin films.The functional properties of polyelectrolyte films (e.g.,controlled release of encapsulated compounds,self-rupturing,biocompatibil-ity and stimuli-responsiveness,etc.)are generally derived from the design and combination of polyelectrolytes [18–21].In some cases,the solubility of the complex formed depends on the pH and the ionic strength of the solution,which was also used for the controlled release of encapsulated compounds or for the stimuli-responsiveness of the thin film.The layer-by-layer method has been also extended to prepare microcapsules using a sacrifice template [22,23].However,the use of a sacrifice template makes it difficult to effectively encapsulate core substrates within a microcapsule.0927-7757/$–see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.colsurfa.2010.08.039Y.Fukui et al./Colloids and Surfaces A:Physicochem.Eng.Aspects370 (2010) 28–3429The strong electrostatic interaction and fast complex-formation between positively and negatively charged polyelectrolytes require the manipulation of each aqueous solution with another immisci-ble phase(e.g.,a water-immiscible organic solvent or a gas phase) when preparing microcapsules composed of polyelectrolytes.The electrospray technique ejects a droplet to a gas phase at high speed and the droplet falls onto a collector vessel.We expected that the electrospray technique would enable the preparation of monodispersed microcapsules based on cationic and anionic polyelectrolytes with high encapsulation efficiency. The present study reports the preparation of microcapsules using several kinds of polyelectrolytes by the electrospray technique. Most of the experiments were performed using chitosan and alginate as polyelectrolytes because this polyelectrolyte combi-nation was widely applied for capsule production,as can be seen in the following references[24–26].We investigated key parameters of the electrospray technique to control the size of microcapsules and found that the electrospray technique could produce monodispersed microcapsules(around100␮m in diam-eter)and also encapsulate various materials(biomacromolecules, microparticles and living cells)within the microcapsules with high encapsulation efficiency.2.Experimental2.1.MaterialsSodium alginate,chitosan,acetic acid and sodium hydrox-ide were purchased from Wako Pure Chemical Industries(Osaka, Japan).Poly(sodium4-styrenesulfonate)(PSS,Mw=∼70,000),poly (allylamine hydrochloride)(PAH,Mw=∼56,000),albumin–fluore-scein isothiocyanate conjugate(albumin–FITC),and tetramethyl-rhodamine isothiocyanate–dextran(TRITC–dextran)with average molecular weights of4400,65,000–76,000and155,000were pur-chased from Sigma(St.Louis,MO).Poly(diallyldimethylammonium chloride)solution(PDDA,Mw=40,000,28wt%in H2O)was pur-chased from Polysciences Inc.(Warrington,PA).Greenfluorescent polystyrene microspheres were purchased as a suspension from Duke Scientific(Palo Alto,CA).The microspheres had a diame-ter of1.9␮m.Yeast extract and peptone were purchased from Becton,Dickinson and Company(Sparks,MD).d-(+)-Glucose was purchased from Nacalaitesque,Inc(Kyoto,Japan).2.2.ElectrosprayThe electrospray(NF-102,MECC Co.,Ogori,Japan)experimen-tal equipment consisted of a syringe pump,a stainless steel needle and a high voltage generator(Fig.1).An anionic or cationic poly-electrolyte aqueous solution was sprayed from a stainless steel needle(cathode)into an aqueous solution containing a polyelec-trolyte with an opposite charge(anode)in a foil-wrapped dish to form polyelectrolyte complex microcapsules.The polyelectrolyte aqueous solution in a dish was stirred continuously and gently (∼100rpm)by a magnetic stirrer bar during electrospraying.Typically,a sodium alginate(1.5wt%)aqueous solution(pH7.5) was sprayed into a chitosan aqueous(0.5wt%)solution(pH3.6) containing200mM acetic acid.The feed rate of the sodium alginate solution was set at0.20mL/h and the working voltage was22.5kV. The distance from the needle to the collector was5.0cm and the inner/outer diameters of a stainless steel needle were130/310␮m. Microcapsules were prepared under different conditions to control the diameters of microcapsules.After electrospraying,microcap-sules were separated from the chitosan solution by centrifugation at100×g for2min.An invertedfluorescence microscope(Olym-pus,IX71)was employed to observe microcapsules.Based on the microscope images,the diameters of more than100microcapsules Fig.1.Illustration of the experimental setup and photograph of a Taylor cone jet (inset).The Taylor cone was observed when a sodium alginate(1.5wt%)aque-ous solution was sprayed at0.20mL/h into a chitosan(0.5wt%)aqueous solution containing200mM acetic acid at a working voltage of22.5kV and a needle-to-collector distance of5cm.The inner/outer diameters of the stainless steel needle were130/310␮m.were measured by an image analysis software,WinROOF(Mitani Corp.,Fukui,Japan).PSS/PAH(PSS sprayed into PAH),PAH/PSS,chitosan/PSS and PDDA/PSS were also used for the preparation of microcapsules.The concentrations of PSS,PAH and PDDA were10wt%.The concentra-tion of chitosan solutions was9wt%.Only the chitosan solution contained50mM acetic acid.The pH of PSS,PAH,PDDA and chi-tosan solutions were4.8,1.6,2.6and6.5,respectively.The feed rate was0.20mL/h in each case,the voltage was24.0kV and the needle-to-collector distance was5.0cm.The inner/outer diameters of a stainless steel needle were330/630␮m.A Taylor cone,formed on the tip of a needle,was observed by a microscope(SKM-2000-PC,Saito Kougaku,Yokohama,Japan).2.3.Encapsulation of polymeric microspheres,protein anddextran and the dextran retention propertiesTo evaluate the encapsulation efficiency,fluorescent micro-spheres,albumin–FITC and TRITC–dextran were used as a core substrate.A sodium alginate(1.5wt%)aqueous solution contain-ing10␮L/mLfluorescent microspheres,10␮g/mL albumin–FITC or10␮g/mL TRITC–dextran was sprayed into0.5wt%chitosan aqueous solution containing200mM acetic acid under typical con-ditions.After spraying,a microcapsule suspension wasfiltered through a nylon-netfilter with a41␮m mesh(Millipore,NY). For the albumin–FITC encapsulation,thefiltrate was adjusted to pH6.0using sodium hydroxide.Non-encapsulatedfluorescence substrates in thefiltrate were quantified using afluorescence spectrometer(LS-50B,PerkinElmer).Fluorescence microspheres, albumin–FITC and TRITC–dextran were excited at468,495and 555nm,respectively.Fluorescence emissions were detected at 508,521and580nm,respectively.Thefluorescent microsphere-,albumin–FITC-and TRITC–dextran-encapsulated microcapsules were observed using a confocal laser scanning microscopy(CLSM) (FV1000-D,Olympus Co.,Tokyo,Japan).30Y.Fukui et al./Colloids and Surfaces A:Physicochem.Eng.Aspects370 (2010) 28–34To determine the dextran retention properties of the microcap-sules,TRITC–dextran-encapsulated microcapsules were collected by centrifugation at100×g for2min and dispersed in3M acetate buffer(pH5.2).Samples were periodically taken from the micro-capsule suspension and centrifuged at100×g.Thefluorescently labeled substrate in the supernatant solution was quantified using afluorescence spectrometer.2.4.Yeast-encapsulated microcapsulesThe yeast Saccharomyces cerevisiae Kyokai No.7was grown in a YPD medium(10g/L yeast extract,20g/L glucose,and20g/L peptone)at30◦C overnight.A sodium alginate(1.5wt%)aqueous solution containing yeast(OD∼0.35)was electrosprayed into a chi-tosan(0.5wt%)aqueous solution containing200mM acetic acid solution under typical conditions.The microcapsules were col-lected by centrifugation at100×g and then immersed in a fresh YPD medium,followed by microscope observation of the yeast growth in microcapsules at25◦C.3.Results and discussionWhen a polyelectrolyte solution is forced through a needle with an electric voltage,the surface tension of the solution becomes equal to the Coulomb repulsion.At this point,the solution at the tip of a needle forms a cone shape,called the“Taylor cone”[27]. If the electricfield intensity is larger than a balance point,small droplets are sprayed spontaneously from the tip of the Taylor cone into a counter electrode.As discussed widely in the literature,the formation of a Taylor cone is essential in electrospray and electro-spinning for the production of droplets andfibers.The formation of a Taylor cone generally requires certain operational conditions, such as particular feed rate,surface tension,conductivity,voltage, and so on[28–30].In the present study,a sodium alginate aque-ous solution was electrosprayed from a needle with a high voltage and the formation of a Taylor cone was also confirmed(inset of Fig.1),similar to previous reports[7,31,32].The charged droplets of the sodium alginate solution contacted the chitosan solution on the counter electrode and each immediately formed a polyelec-trolyte complex by an electrostatic interaction at the interface of the alginate solution/chitosan solution,resulting in a microcapsule. The alginate/chitosan microcapsules obtained by electrospray are shown in Fig.2a.The diameters of the microcapsules were from115 to145␮m,with a relatively narrow diameter distribution(Fig.2b), giving a coefficient of variation(CV)of only8.0%.These results indicate that the electrospray technique continuously produced aqueous droplets of a uniform size and that the droplets sprayed into the atmosphere reached the chitosan solution without expe-riencing droplet coalescence in the atmosphere during theirflight, probably due to the repulsion between charged droplets[33].We then investigated the effects of the operational conditions on the diameter of alginate/chitosan microcapsules.When varying one of the parameters,the other parameters were kept the same as those in Fig.2.Fig.3a shows the effect of feed rate on the diameter of the micro-capsules.The diameter of the microcapsules decreased from130 to80␮m with decreasing feed rate.The standard deviation also decreased with the diameter of microcapsules.Next,the effect of the working voltage on the diameter of microcapsules was stud-ied(Fig.3b).In the absence of a working voltage,the diameter of the microcapsules was around2.0mm,which agreed with previous reports[15,16].The electrostatic repulsions at the liquid level on the Taylor cone became stronger as the voltage increased,so that the droplets became smaller.As a result,the diameter of the result-ing microcapsules decreased with increasing voltage.As shownin Fig.2.(a)Microscope image and(b)size distribution of alginate/chitosan micro-capsules prepared by electrospray.Operating conditions:1.5wt%sodium alginate (0.2mL/h),0.5wt%chitosan,voltage22.5kV,needle-to-collector distance5cm,and inner/outer needle diameters130/310␮m.The scale bar represents100␮m.Fig.3c,we examined the effect of the needle-to-collector distance on the diameter of microcapsules.The diameter decreased with decreasing distance.This was probably due to the same reasons as given above for the effect of the working voltage:the shorter distance,the stronger the intensity of the electricfield.Fig.3d shows the effect of the inner diameter of the needle(130, 190,330and900␮m).The diameter of microcapsules increased linearly as the inner diameter of the needle increased from130to 330␮m.When a needle with an inner diameter of900␮m was used,the microcapsules were polydisperse(CV=39.3%).This is because the Taylor cone became unstable when large needle diam-eters were used.Interestingly,the diameters of the microcapsules were nearly the same as or smaller than the inner diameters of needles,even though there was negligible evaporation of water.In other meth-ods(e.g.,membrane emulsification,coacervation and microfluidic techniques),it was not possible to produce microcapsules smaller than the nozzle or pore diameter.This feature of the electrospray technique suggests the production of microcapsules and micro-spheres smaller than the limitations of microfabrication techniques is possible and this would be a great advantage in controlling the diameter of microcapsules and microspheres.The effect of the sodium alginate concentration(1.0,1.5,2.0wt%) was studied(Fig.3e).The pH of each sodium alginate solution was around7.5.At a sodium alginate concentration of1.0wt%, the mean diameter of microcapsules was95␮m with a CV of18%,Y.Fukui et al./Colloids and Surfaces A:Physicochem.Eng.Aspects370 (2010) 28–3431Fig.3.Effects of electrospray operating conditions on the diameter of microcapsules.(a)Feed rate,(b)working voltage,(c)needle-to-collector distance,(d)inner diameter of needle,(e)concentration of sodium alginate,(f)concentration of chitosan.Typical operating conditions were1.5wt%sodium alginate(0.2mL/h),0.5wt%chitosan,working voltage22.5kV and needle-to-collector distance5cm.Needle inner/outer diameters were130/310␮m.while the CV at1.5and2.0wt%were only9.9and9.3%,respec-tively.At0.5wt%,no spherical microcapsules were observed.When the concentration of sodium alginate is low,an alginate/chitosan complex would be formed but such a complex might be soluble in the chitosan solution because of the excess amount of polyca-tions present.The concentration of the chitosan solution,which received the droplets of alginate solution,also affected the diam-eters of microcapsules(Fig.3f).When the chitosan concentration was set at1.0,1.5and2.0wt%(pH3.9,4.1and4.3),the diame-ters of microcapsules were relatively small and there were many non-spherical microcapsules(inset of Fig.3f).The spherical micro-capsules were formed at0.5wt%chitosan solution(pH3.6).It can be presumed that the shape of microcapsules depends on the forma-tion rate and mechanical strength of the polyelectrolyte complex [34,35].There is room for further investigation on the mechanism of the microcapsule formation considering the formation rate and the mechanical strength of the polyelectrolyte complex.Not only the combination of alginate/chitosan but various other combinations of polyelectrolytes were also employed to pre-pare polyelectrolyte microcapsules.The combination of PSS/PAH (PSS sprayed into PAH),PAH/PSS,chitosan/PSS and PDDA/PSS were investigated(Fig.4).Although the combination of PSS/PAH (Fig.4d)also produced observable microcapsules,they had insuf-ficient mechanical strength for manipulation by pipetting.While a polyanion solution was sprayed into a polycation solution in the above investigations,we also sprayed a polycationic aque-32Y.Fukui et al./Colloids and Surfaces A:Physicochem.Eng.Aspects370 (2010) 28–34Fig.4.Microscope images of microcapsules produced from (a)PAH/PSS,(b)PDDA/PSS,(c)chitosan/PSS,(d)PSS/PAH.The concentrations of PAH,PSS and PDDA solutions were 10wt%and the concentration of chitosan solution was 9wt%,the feed rate was 0.20mL/h,the working voltage was 24.0kV and the needle-to-collector distance was 5.0cm.The inner/outer diameters of the needle were 330/630␮m.The scale bars represent 100␮m.ous solution into a polyanionic aqueous solution.As shown in Fig.4a,PAH/PSS microcapsules were successfully prepared.The mean diameter of the resultant microcapsules was 210␮m and the CV was 22%.Chitosan/PSS microcapsules (Fig.4c)were also prepared but were polydispersed.One of the reasons for the poly-dispersed chitosan/PSS microcapsules may have been that the lack of a balance of forces leading to an unstable Taylor cone,caused by high viscosity of the chitosan solution.The combination of PDDA/PSS (Fig.4b)produced microcapsules but their mechani-cal strength was as low as that of the PSS/PAH microcapsules (Fig.4d).Finally,we investigated the encapsulation of protein,dextran and cells in the polyelectrolyte microcapsules by electrospray.When protein,dextran and cells are encapsulated,the encapsula-tion efficiency and the residual activity are of considerable practical importance.In this electrospray technique,no organic solvent,heat or vacuum for drying are required.Therefore,it is expected that this method would be suitable for encapsulation of physi-ologically active substances and cells.In this study,fluorescent microspheres,albumin–FITC,TRITC–dextran and yeast cells were used as core substrates and a sodium alginate solution containing each core substrate was electrosprayed into a chitosan solution.Taking into account the capsule morphology,the productivity and stability of Taylor cone,the following production parameters were chosen to prepare alginate/chitosan microcapsules encapsulating the substrates;the concentrations of sodium alginate and chi-tosan were 1.5,0.5wt%,respectively,the feed rate of the sodium alginate solution was set at 0.20mL/h,the working voltage was 22.5kV,the distance from the needle to the collector was 5.0cm and the inner/outer diameters of a stainless steel needle were 130/310␮m.To approximate the encapsulation efficiency of yeast cells,we measured that of fluorescent microspheres because the size of fluorescent microspheres and yeast cells are nearly equal (a couple of micrometers).The CLSM images of the microcap-sules revealed that these fluorescent substances (the fluorescent microspheres and albumin–FITC)were uniformly spread over the whole microcapsules composed of alginate/chitosan,meaning that these substances were successfully encapsulated in the monodis-persed microcapsules (Fig.5).The encapsulation efficiency of microspheres and albumin was >99%.It should be noted that the diameters of the microcapsules and the size distribution were not affected by the presence of core substrates.These results demon-strate that the electrospray technique can encapsulate micro-and nano-sized materials in polyelectrolyte microcapsules with a high encapsulation efficiency.The retention of TRITC–dextran with different molecular weights in microcapsules was investigated.The retention ratios of all types of TRITC–dextran (Mw =4400,65,000–76,000and 155,000)in sodium alginate/chitosan microcapsules were >99%at 24h after dispersing microcapsules in an acetate buffer.Pre-vious studies reported that the ultrathin films of polyelectrolytes prepared by the layer-by-layer method displayed similarly high rejection properties to nanofiltration membranes [36–38].The high retention properties of the microcapsules in the present study were therefore reasonable.Fig.6shows phase-contrast microscope images of microcap-sules encapsulating yeast in a YPD medium at different periods after microcapsule preparation.As is evident from these images,yeast cells were also successfully encapsulated in the alginate/chitosan microcapsules and they grew inside the microcapsules over time.The image at 0h and the results from fluorescent microspheres allow us to speculate that most of cells sprayed were encapsulated within the microcapsules.The growth of yeast in a microcap-sule indicates sufficient penetration of low-molecular materials (glucose,peptone,etc.)from the culture medium through the microcapsule shell consisting of the alginate/chitosan complex.Even after 48h,microcapsules containing yeast cells did not tear,which indicates considerable mechanical strength of the algi-nate/chitosan microcapsules.These results demonstrate that the electrospray technique achieves the encapsulation of a physiolog-ically active substrate into polyelectrolyte microcapsules without any critical damage to the substrate.In summary,we prepared microcapsules based on cationic and anionic polyelectrolytes by the electrospray technique.The electrospray technique produced monodispersed alginate/chitosan microcapsules,whose size was controlled by varying the operatingY.Fukui et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 370 (2010) 28–3433Fig.5.CLSM microscope images of alginate/chitosan microcapsules containing (a)and (b)fluorescent microspheres,(c)albumin–FITC,(d)TRITC–dextran (Mw =155,000).Operating conditions were the same as those in Fig.2.The scale bars represent 100␮m.conditions.This technique can utilize various types of natural and synthetic polyelectrolytes,and also encapsulate various substrates (biomacromolecules,microspheres and living cells)in the micro-capsules with high encapsulation efficiency and without critical damage to the substrates.Due to the simplicity of the electro-spray setup and the attractive properties discussed above,the electrospray technique is expected to be a practical method for the industrial production ofmicrocapsules.Fig.6.Phase-contrast images of yeast-encapsulated microcapsules in YPD media at different periods after the preparation of microcapsules.(a)0h,(b)8h,(c)16h,(d)24h.Operating conditions were the same as those in Fig.2.The scale bars represent 100␮m.34Y.Fukui et al./Colloids and Surfaces A:Physicochem.Eng.Aspects370 (2010) 28–34AcknowledgmentsWe thank Professor M.Kotaki at Kyoto Institute of Technology for the technical support.This work was supportedfinancially by Special Coordination Funds for Promoting Science and Technol-ogy,Creation of Innovation Centers for Advanced Interdisciplinary Research Areas(Innovative Bioproduction Kobe),MEXT,Japan.This work was partially supported by the Kao Foundation for Arts and Sciences.The present work was also partially supported by Grants for Research and Technology Development on Waste Management (K2119)from the Ministry of Environment,Japan.References[1]N.J.Zuidam,V.Nedovic,Encapsulation Technologies for Active Food Ingredientsand Food Processing,first ed.,Springer,2009.[2]M.Rosen,Delivery System Handbook for Personal Care and Cosmetic Products:Technology,Applications and Formulations,William Andrew,2006.[3]F.Lim,A.M.Sun,Microencapsulated islets as bioartificial endocrine pancreas,Science210(1980)908–910.[4]R.M.Shah,A.P.D’mello,Strategies to maximize the encapsulation efficiencyof phenylalanine ammonia lyase in microcapsules,Int.J.Pharm.356(2008) 61–68.[5]N.Gaponik,I.L.Radtchenko,M.R.Gerstenberger,Y.A.Fedutik,G.B.Sukho-rukov,A.L.Rogach,Labeling of biocompatible polymer microcapsules with near-infrared emitting nanocrystals,Nano Lett.3(2003)369–372.[6]L.Y.Chu,T.Yamaguchi,S.Nakao,A molecular-recognition microcapsule forenvironmental stimuli-responsive controlled release,Adv.Mater.14(2002) 386–389.[7]I.G.Loscertales,A.Barrero,I.Guerrero,R.Cortijo,M.Marquez,A.M.Ganan-Calvo,Micro/nano encapsulation via electrified coaxial liquid jets,Science295 (2002)1695–1698.[8]H.Zhang, E.Tumarkin,R.Peerani,Z.Nie,R.M.A.Sullan,G.C.Walker, E.Kumacheva,Microfluidic production of biopolymer microcapsules with con-trolled morphology,J.Am.Chem.Soc.128(2006)12205–12210.[9]Z.Nie,S.Xu,M.Seo,P.C.Lewis,E.Kumacheva,Polymer particles with variousshapes and morphologies produced in continuous microfluidic reactors,J.Am.Chem.Soc.127(2005)8058–8063.[10]B.Bugarski,Q.Li,M.F.A.Goosen,D.Poncelet,R.J.Neufeld,G.Vunjak,Electro-static droplet generation:mechanism of polymer droplet formation,AIChE J.40(1994)1026–1031.[11]V.A.Nedovic,B.Obradovic,I.Leskosek-Cukalovic,O.Trifunovic,R.Pesic,B.Bugarski,Electrostatic generation of alginate microbeads loaded with brewing yeast,Process Biochem.37(2001)17–22.[12]V.Manojlovic,J.Djonlagic,B.Obradovic,V.Nedovic,B.Bugarski,Investiga-tions of cell immobilization in alginate:rheological and electrostatic extrusion studies,J.Chem.Technol.Biotechnol.81(2006)505–510.[13]H.R.Brandenberger,F.Widmer,Immobilization of highly concentrated cell sus-pensions using the laminar jet breakup technique,Biotechnol.Progr.15(1999) 366–372.[14]J.W.Xie,C.H.Wang,Electrospray in the dripping mode for cell microencapsu-lation,J.Colloid Interface Sci.312(2007)247–255.[15]B.Philipp,H.Dautzenberg,K.J.Linow,J.Kotz,W.Dawydoff,Polyelectrolytecomplexes—recent developments and open problems,Prog.Polym.Sci.14 (1989)91–172.[16]R.Pommersheim,J.Schrezenmeir,W.Vogt,Immobilization of enzymes bymultilayer microcapsules,Macromol.Chem.Phys.195(1994)1557–1567.[17]G.Decher,Fuzzy nanoassemblies:toward layered polymeric multicomposites,Science277(1997)1232–1237.[18]K.C.Wood,J.Q.Boedicker,D.M.Lynn,P.T.Hammond,Tunable drug releasefrom hydrolytically degradable layer-by-layer thinfilms,Langmuir21(2005) 1603–1609.[19]H.Huang,E.Pierstorff,E.Osawa,D.Ho,Protein-mediated assembly of nanodi-amond hydrogels into a biocompatible and biofunctional multilayer nanofilm, ACS Nano2(2008)203–212.[20]D.Volodkin,Y.Arntz,P.Schaaf,H.Moehwald,J.C.Voegel,V.Ball,Compos-ite multilayered biocompatible polyelectrolytefilms with intact liposomes: stability and temperature triggered dye release,Soft Matter4(2008)122–130.[21]C.T.Yang,Y.Wang,S.Yu,Y.C.I.Chang,Controlled molecular organization ofsurface macromolecular assemblies based on stimuli-responsive polypeptide brushes,Biomacromolecules10(2008)58–65.[22]F.Caruso,R.A.Caruso,H.Mohwald,Nanoengineering of inorganic andhybrid hollow spheres by colloidal templating,Science282(1998)1111–1114.[23]F.Caruso,H.Lichtenfeld,M.Giersig,H.Mohwald,electrostatic self-assembly ofsilica nanoparticle polyelectrolyte multilayers on polystyrene latex particles,J.Am.Chem.Soc.120(1998)8523–8524.[24]S.Ye,C.Wang,X.Liu,Z.Tong,Multilayer nanocapsules of polysaccharidechitosan and alginate through layer-by-layer assembly directly on PS nanopar-ticles for release,J.Biomater.Sci.,Polym.Ed.16(2005)909–923.[25]K.Y.Lee,W.H.Park,W.S.Ha,Polyelectrolyte complexes of sodium alginate withchitosan or its derivatives for microcapsules,J.Appl.Polym.Sci.63(1997) 425–432.[26]O.Gaserod,O.Smidsrod,G.Skjak-Braek,Microcapsules of alginate–chitosan–I.A quantitative study of the interaction between alginate and chitosan, Biomaterials19(1998)1815–1825.[27]G.Taylor,Disintegration of water drops in an electricfield,Proc.R.Soc.Lond.A280(1964)383–397.[28]J.F.Delamora,I.G.Loscertales,The current emitted by highly conducting Taylorcones,J.Fluid Mech.260(1994)155–184.[29]R.P.A.Hartman,D.J.Brunner,D.M.A.Camelot,J.C.M.Marijnissen,B.Scarlett,Jetbreak-up in electrohydrodynamic atomization in the cone-jet mode,J.Aerosol Sci.31(2000)65–95.[30]A.M.GananCalvo,J.Davila,A.Barrero,Current and droplet size in the electro-spraying of liquids.Scaling laws,J.Aerosol Sci.28(1997)249–275.[31]R.Bocanegra,A.G.Gaonkar,A.Barrero,I.G.Loscertales,D.Pechack,M.Marquez,Production of cocoa butter microcapsules using an electrospray process,J.Food Sci.70(2005)492–497.[32]K.H.Roh, D.C.Martin,hann,Biphasic Janus particles with nanoscaleanisotropy,Nat.Mater.4(2005)759–763.[33]A.Jaworek, A.T.Sobczyk,Electrospraying route to nanotechnology:anoverview,J.Electrostat.66(2008)197–219.[34]V.D.Gordon,X.Chen,J.W.Hutchinson,A.R.Bausch,M.Marquez,D.A.Weitz,Self-assembled polymer membrane capsules inflated by osmotic pressure,J.Am.Chem.Soc.126(2004)14117–14122.[35]O.I.Vinogradova,O.V.Lebedeva,B.S.Kim,Mechanical behavior and character-ization of microcapsules,Annu.Rev.Mater.Res.36(2006)143–178.[36]W.Q.Jin,A.Toutianoush,B.Tieke,Use of polyelectrolyte layer-by-layer assem-blies as nanofiltration and reverse osmosis membranes,Langumir19(2003) 2550–2553.[37]S.U.Hong,ler,M.L.Bruening,Removal of dyes,sugars,and aminoacids from NaCl solutions using multilayer polyelectrolyte nanofiltration mem-branes,Ind.Eng.Chem.Res.45(2006)6284–6288.[38]S.U.Hong,R.Malaisamy,M.L.Bruening,Separation offluoride from othermonovalent anions using multilayer polyelectrolyte nanofiltration mem-branes,Langumir23(2007)1716–1722.。