Synthesis of pH-Responsive Shell Cross-Linked Micelles and Their Use as Nanoreactors for the Preparation of Gold
Nanoparticles
Shiyong Liu,Jonathan V.M.Weaver,Maud Save,and Steven P.Armes* School of Chemistry,Physics and Environmental Science,University of Sussex,
Brighton,East Sussex,BN19QJ,United Kingdom
Received May28,2002.In Final Form:August14,2002
Poly[(ethylene oxide)-block-glycerol monomethacrylate-block-2-(diethylamino)ethyl methacrylate](PEO-GMA-DEA)and poly[(ethylene oxide)-block-2-hydroxyethyl methacrylate-block-2-(diethylamino)ethyl methacrylate](PEO-HEMA-DEA)triblock copolymers were synthesized directly,without recourse to protecting group chemistry,via atom transfer radical polymerization by successive polymerization of GMA (or HEMA)and DEA monomers using a PEO-based macroinitiator.These triblock copolymers dissolved molecularly in aqueous solution at low pH;on addition of NaOH,micellization occurred above pH7-8to form three-layer“onionlike”micelles comprising DEA cores,GMA(or HEMA)inner shells,and PEO outer coronas.Selective cross-linking of the GMA(or HEMA)inner shell was successfully achieved by adding divinyl sulfone[DVS]to the alkaline micellar solution at room temperature.Unexpectedly,the PEO-HEMA-DEA triblock proved to be much less reactive toward DVS than the two PEO-GMA-DEA triblocks, and an excess of DVS was required to prepare shell cross-linked(SCL)micelles using the former triblock. The resulting SCL micelles exhibited reversible swelling behavior on varying the solution pH.At low pH, the DEA cores became protonated and hence hydrophilic.The effect of varying the block composition and the[DVS]/[GMA]molar ratio on the structural stability and pH-dependent(de)swelling of the SCL micelles was studied.Longer DEA blocks and lower[DVS]/[GMA]molar ratios led to increased swellability,as expected.Finally,these SCL micelles can serve as nanoreactors for the synthesis of gold nanoparticles. The basic DEA residues in the cores of the SCL micelles were first protonated using HAuCl4,and then the electrostatically bound AuCl4-anions were reduced to nanoparticles of elemental gold using NaBH4 at neutral pH.The gold-loaded SCL micelles exhibited excellent long-term colloid stability.
Introduction
Shell cross-linked(SCL)micelles combine the properties of micelles,microgels,nanoparticles,and dendrimers,and various applications such as targeted drug delivery, sequestration of metabolites,and entrapment of envi-ronmental pollutants have been suggested.1-4In particu-lar,recent efforts have focused on the synthesis of SCL micelles that have either hollow cores5,6or tunably hydrophilic cores.7-9Both Wooley’s group5and Liu and co-workers6have prepared hollow SCL micelles by selec-tive chemical degradation of the core-forming block, whereas SCL micelles with tunably hydrophilic cores have been synthesized either by in situ deprotection of a hydrophobic core-forming block7,8or by use of core-forming blocks which exhibit dual hydrophilic/hydrophobic char-acter.9In principle,hollow SCL micelles offer larger loading capacities,but tunable hydrophilic cores are also attractive since no core removal step is required and there is the potential for the triggered release of encapsulated actives via various chemical stimuli(pH,temperature, ionic strength,etc.).
In1998,our group described the first example of synthesis of SCL micelles with tunable core hydrophilic-ity.9a An aqueous micellar solution of partially quaternized poly[2-(dimethylamino)ethyl methacrylate-block-2-(N-morpholino)ethyl methacrylate](DMA-MEMA)was re-acted with a bifunctional cross-linker,1,2-bis(2-iodoethoxy)-ethane(BIEE),in aqueous solution at60°C.Under these conditions,the MEMA block is above its cloud point and forms the micelle cores.On cooling to20°C,the hydro-phobic MEMA micelle cores become hydrated.Thus the SCL micelle cores could be reversibly(de)hydrated depending on the solution temperature.
One major drawback in early syntheses of SCL micelles was that shell cross-linking had to be carried out at high dilution(typically<0.50%solids)in order to avoid extensive intermicellar cross-linking.Clearly,unless this problem was addressed,the synthesis of SCL micelles was unlikely to be commercially viable,even for specialty applications.Fortunately,we recently demonstrated that ABC triblock copolymers offer great advantages over conventional AB diblock copolymers,since the former allow shell cross-linking to be carried out at high solids with
*To whom correspondence should be addressed.Tel:
UK+1273-678650Fax:UK+1273-677196.E-mail:S.P.Armes@
https://www.doczj.com/doc/822959411.html,.
(1)(a)Thurmond,K.B.;Kowalewski,T.;Wooley,K.L.J.Am.Chem.
Soc.1996,118,7239.(b)Wooley,K.L.J.Polym.Sci.,Part A:Polym.
Chem.2000,38,1397.
(2)(a)Thurmond,K.B.;Kowalewski,T.;Wooley,K.L.J.Am.Chem.
Soc.1997,119,6656.(b)Huang,H.;Remsen,E.E.;Wooley,K.L.Chem.
Commun.1998,1415.(c)Huang,H.;Remsen,E.E.;Kowalewski,T.;
Wooley,K.L.J.Am.Chem.Soc.1999,121,3805.(d)Ma,Q.;Wooley,
K.L.J.Polym.Sci.,Part A:Polym.Chem.2000,38,4805.(e)Becker,
M.L.;Remsen,E.E.;Wooley.K.L.J.Polym.Sci.,Part A:Polym.Chem.
2001,39,4152.(e)Ma,Q.;Remsen,E.E.;Kowalewski,T.;Wooley,K.
L.J.Am.Chem.Soc.2001,123,4627.
(3)(a)Sanji,T.;Nakatsuka,Y.;Kitayama,F.;Sakurai,H.Chem.
Commun.1999,2201.(b)Sanji,T.;Nakatsuka,Y.;Ohnishi,S.;Sakurai,
H.Macromolecules2000,33,8524.
(4)Underhill,R.S.;Liu,G.Chem.Mater.2000,12,2082.
(5)(a)Huang,H.;Remsen,E.E.;Kowalewski,T.;Wooley,K.L.J.
Am.Chem.Soc.1999,121,3805.(b)Zhang,Q.;Remsen,E.E.;Wooley,
K.L.J.Am.Chem.Soc.2000,122,3642.
(6)Ding,J.;Liu,J.J.Phys.Chem.B1998,102,6107.
(7)Ma,Q.;Remsen,E.E.;Kowalewski,T.;Schaefer,J.;Wooley,K.
L.Nano Lett.2001,1,651.
(8)Zhang,Z.;Liu,G.;Bell,S.Macromolecules2000,33,7877.
(9)(a)Bu¨tu¨n,V.;Billingham,N.C.;Armes,S.P.J.Am.Chem.Soc.
1998,120,12135.(b)Bu¨tu¨n,V.;Lowe,A.B.;Billingham,N.C.;Armes,
S.P.J.Am.Chem.Soc.1999,121,4288.
8350Langmuir2002,18,8350-8357
10.1021/la020496t CCC:$22.00?2002American Chemical Society
Published on Web09/27/2002
little or no intermicellar cross-linking.In a proof-of-concept study,a poly(ethylene oxide)(PEO)-DMA-MEMA tri-block copolymer was cross-linked at a copolymer concen-tration of10%w/v with negligible intermicellar cross-linking.10This is because the coronal PEO chains prevented interpenetration of the micelles due to a steric stabilization mechanism which in turn ensured that only localized,intramicellar cross-linking occurred.In view of this success,all of our current synthetic effort is now devoted to the synthesis of ABC triblock copolymers,rather than AB diblocks.
The synthesis of well-defined block copolymers requires either living or pseudo-living polymerization chemistry. Given the stringent purification required for ionic poly-merizations,increasing attention is now being given to the use of atom transfer radical polymerization(ATRP)11 for the preparation of the block copolymer precursors that are required for SCL micelle syntheses.2d,2e,7,8,12At Sussex, we have recently developed ATRP for the efficient po-lymerization of hydrophilic monomers in either water or alcoholic media at room temperature.12-17
To date,we have used BIEE as a bifunctional cross-
linking agent in all of our SCL micelle studies.9,16 Generally,BIEE has been used to cross-link DMA residues via quaternization,but it can also react efficiently with methacrylic acid residues,forming ester linkages.9How-ever,in view of its cost,toxicity,limited water solubility, and likely mutagenicity,BIEE is highly unlikely to be employed in commercial applications of SCL micelles, particularly for use in the biomedical field.The alternative cross-linking strategies described in the literature are equally unsatisfactory.For example,Wooley’s group1,2use carbodiimide coupling chemistry to link carboxylic acid groups via diamines(obvious disadvantages here are the cost of the reagents and the cleanup requirements when dealing with several molecular species),whereas Liu and co-workers4,6prefer the UV-induced coupling of cinnamoyl groups,which are too hydrophobic to be suitable for use in aqueous media.Thus it is indisputable that new, improved cross-linking strategies are urgently required. The ideal cross-linker should be water-soluble,nontoxic, and cost-effective.The cross-linking chemistry should be facile under mild conditions(e.g.,aqueous solution and ambient temperature),produce no small molecule byprod-ucts,and preferably be potentially reversible.We have examined several new strategies,and in this work we describe the use of divinyl sulfone(DVS)to selectively cross-link hydroxylated blocks(Figure1a).This reagent has been previously used for the preparation of gels,18microgels,19and nanoparticle networks20from hydroxyl-containing precursors21,22but never,as far as we are aware, employed for the synthesis of SCL micelles.
In the present study,we describe the efficient synthesis of SCL micelles with pH-responsive cores from novel ABC triblock copolymers prepared via ATRP.The triblock copolymers are based on either poly[(ethylene oxide)-block-glycerol monomethacrylate-block-2-(diethylamino)-ethyl methacrylate](PEO-GMA-DEA)or poly[(ethylene oxide)-block-2-hydroxyethyl methacrylate-block-2-(dieth-ylamino)ethyl methacrylate](PEO-HEMA-DEA).The pH-induced micellization of these copolymers and the subsequent shell cross-linking of the GMA(or HEMA) inner shell with DVS were studied in detail.The effect of varying the relative block compositions and the[DVS]/ [GMA](or[DVS]/[HEMA])molar ratio on the pH-induced (de)swelling of the SCL micelles was also investigated. Figure2shows the reaction scheme for the preparation of SCL micelles from the hydroxy-functionalized triblock copolymers.
Experimental Section
Materials.GMA monomer was kindly donated by Ro¨hm (Germany).HEMA monomer and monohydroxy-capped poly-(ethylene oxide)(PEO45-OH)[mean degree of polymerization) 45,M w/M n) 1.10]were donated by Laporte Performance Chemicals(Hythe,U.K).DEA was purchased from Aldrich.These monomers were treated with basic alumina and then vacuum-distilled from CaH2and stored at-20°C prior to use.Cu I Cl, 2,2′-bipyridine(bpy),2-bromoisobutyryl bromide,triethylamine, and DVS were purchased from Aldrich and used without further purification.
Preparation of PEO Macroinitiator(1).In a typical example,PEO45-OH(50.0g,0.025mol)was dissolved in300 mL of toluene in a500mL three-neck flask.After azeotropic distillation of30-40mL of toluene at reduced pressure to remove traces of water,triethylamine(4.17mL,0.03mol)was added and the solution mixture was cooled to0°C.Then2-bromoisobu-tyryl bromide(3.7mL,0.03mol)was added dropwise via syringe over1h,and the reaction mixture was stirred overnight at room temperature.The stirred solution was treated with charcoal, which was subsequently removed by filtration,and most of the toluene was removed by rotary evaporation prior to precipitation
(10)Bu¨tu¨n,V.;Wang,X.-S.;de Paz Ba′nez,M.V.;Robinson,K.L.; Billingham,N.C.;Armes,S.P.Macromolecules2000,33,1.
(11)(a)Wang,J.S.;Matyjaszewski,K.J.Am.Chem.Soc.1995,117, 5614.(b)Kato,M.;Kamagaito,M.;Sawamoto,M.;Higashimura,H. Macromolecules1995,28,1721.(c)Haddleton,D.M.;Waterson,C.; Derrick,P.J.;Jasieczek,C.B.;Shooter,https://www.doczj.com/doc/822959411.html,mun.1997, 683.(d)Patten,T.E.;Matyjaszewski,K.Adv.Mater.1998,10,901.(e) Sawamoto,M.;Kamagaito,M.Trends Polym.Sci.1996,4,371.(f) Matyjaszewski,K.;Xia,J.H.Chem.Rev.2001,101,2921.
(12)(a)Wang,X.-S.;Lascelles,S.F.;Jackson,R.A.;Armes,S.P. https://www.doczj.com/doc/822959411.html,mun.1999,1817.(b)Wang,X.-S.;Jackson,R.A.;Armes, S.P.Macromolecules2000,33,255.(c)Wang,X.-S.;Armes,S.P. Macromolecules2000,33,6640.
(13)Robinson,K.L.;de Paz-Ba′nez,M.V.;Wang,X.S.;Armes,S.P. Macromolecules2001,34,5799.
(14)Save,M.;Weaver,J.V.M.;Armes,S.P.;McKenna,P. Macromolecules2002,35,1152.
(15)Lobb,E.J.;Ma,I.;Billingham,N.C.;Armes,S.P.J.Am.Chem. Soc.2001,123,7913.
(16)Liu,S.;Armes,S.P.J.Am.Chem.Soc.2001,123,9910.
(17)(a)Liu,S.;Billingham,N.C.;Armes,S.P.Angew.Chem.,Int. Ed.2001,40,2328.(b)Liu,S.;Armes,S.P.Angew.Chem.,Int.Ed. 2002,41,1413.
(18)Anbergen,U.;Oppermann,W.Polymer1990,1854.
(19)Lu,X.;Hu,Z.;Gao,J.Macromolecules2000,33,8698.
(20)Hu,Z.;Lu,X.;Gao,J.Adv.Mater.2001,13,1708.
(21)Holst,A.Angew.Makromol.Chem.1979,76/77,177.
(22)Suter,C.M.The Organic Chemistry of Sulfur,Tetracovalent Sulfur Compounds,2nd ed.;John Wiley&Sons:London,
1945. Figure1.(a)Reaction scheme for cross-linking of the hydroxy-functional triblock copolymers with DVS;(b)side reaction of DVS in aqueous solution at neutral and alkaline pH.
pH-Responsive Shell Cross-Linked Micelles Langmuir,Vol.18,No.22,20028351
into a 10-fold excess of ether.The crude polymer was dried under vacuum,dissolved in water at pH 8-9,and then extracted with dichloromethane.The organic layers were collected and dried over MgSO 4,and removal of the solvent under vacuum led to isolation of the purified macroinitiator (PEO 45-Br).
Preparation of PEO -GMA -DEA and PEO -HEMA -DEA Triblock Copolymers.The typical procedure was as follows.The PEO 45-Br macroinitiator and GMA or HEMA monomer were added to one reaction flask and were degassed under nitrogen purge.Methanol was degassed separately and added to the monomer/initiator mixture via a double-tipped needle,followed by a freeze -pump -thaw cycle.The Cu I Br and bpy catalysts were introduced into the reaction flask to start the polymerization at room temperature.The monomer concentration was 37%w/v.After the conversion of GMA (or HEMA)had reached more than 95%,23degassed DEA monomer diluted with methanol (1/1v/v)was transferred to the reaction flask via a double-tipped needle.After another 12-15h,the dark brown reaction solution was exposed to air and diluted with methanol;termination occurred rapidly,as indicated by the color change from brown to blue due to the aerial oxidation of Cu(I)to Cu(II).The triblock copolymer was purified by passing through a silica gel column to remove the copper catalyst.After evaporating all the solvent,drying in a vacuum oven at room temperature yielded colorless polymer.For gel permeation chromatography (GPC)analysis using tetrahydrofuran (THF)as the eluent,the GMA residues in the PEO -GMA -DEA triblock copolymers were derivatized by reacting with a 4-fold excess of benzoic anhydride in pyridine,
as previously described.14The modified triblock copolymers exhibit symmetrical,unimodal GPC traces,and there is no evidence for any residual PEO 45-Br macroinitiator,suggesting high initiation efficiency.Moreover,compared to the GPC traces obtained for the PEO -GMA or PEO -HEMA diblock precursors,there is a clear shift to higher molecular weights for the triblock copolymers,which had relatively narrow final polydispersities.All of these data indicated that the syntheses of the triblock copolymers had been successful.Table 1summarizes the molecular weight data for the three PEO -GMA -DEA and PEO -HEMA -DEA triblock copolymers examined in this study.Preparation of Micelles and SCL Micelles.The PEO -GMA -DEA triblock copolymers were molecularly dissolved in water at pH 2at various copolymer concentrations,and the solution pH was adjusted to pH 12so as to induce micelle formation.Shell cross-linking was achieved by adding DVS,and the reaction solutions were stirred for 3-4h at room temperature.For the HEMA-based triblock copolymer,the target degree of cross-linking is given by y )2[DVS]/[HEMA]×100%.Assuming that the secondary hydroxy groups in the GMA residues are much less reactive than the primary hydroxy groups,the analogous equation for the GMA-based triblock is y )2[DVS]/[GMA]×100%.However,we do not know whether this assumption of differential reactivity is valid.Moreover,it is quite likely that some (unknown)fraction of the DVS may react with hydroxy groups on the same GMA or HEMA chain and will not therefore contribute to shell cross-linking.Furthermore,the DVS is prone to hydrolysis under the cross-linking conditions (see Figure 1),which is likely to reduce the actual degree of cross-linking achieved.In view of these uncertainties,we have chosen to cite the initial molar ratio of reacting groups ([DVS]/[HEMA]
(23)We have previously studied the kinetics of polymerization of both GMA and HEMA by ATRP in some detail;see refs 13and
14.Figure 2.(a)Reaction scheme for the synthesis of the PEO -GMA -DEA triblock copolymers;(b)schematic illustration of the formation of three-layer onionlike micelles and shell cross-linked micelles from PEO -GMA -DEA triblock copolymers.
Table 1.Molecular Parameters of the Three Triblock Copolymers Used in This Study a
sample code DP of PEO block
DP of second block
DP of DEA block
M n,cal M n,GPC M w /M n PEO 45-GMA 40-DEA 5545405525200b 19400c 1.23PEO 45-GMA 25-DEA 7045257023300b 25500c 1.26PEO 45-HEMA 30-DEA 50
45
30
50
15200
15700d
1.17
a
DP refers to the number-average degree of polymerization.b Theoretical calculated molecular weight assuming that all GMA residues are derivatized with benzoic anhydride.c THF GPC for the two derivatized GMA-based triblock copolymers.d THF GPC for the underivatized HEMA-based triblock copolymer.
8352Langmuir,Vol.18,No.22,2002Liu et al.
or[DVS]/[GMA])used to synthesize the SCL micelles,rather than the target degree of shell cross-linking.
In preliminary experiments,it was found that the PEO-HEMA-DEA triblock did not dissolve molecularly in aqueous acidic solution(pH2)at20°C;dynamic light scattering studies indicated some degree of weak aggregation.The origin of this aggregation is not known,but it may involve hydrogen bonding between the PEO block and the HEMA residues.Alternatively, the relatively low cloud point of the HEMA block with a Dp of 30(approximately36°C24)may be important.Fortunately, further studies confirmed that molecular dissolution could be achieved in cold aqueous acidic solution(around5°C and pH2). Addition of base at5°C led to the formation of colloidally stable DEA-core micelles in alkaline media;these micelles were allowed to warm to ambient temperature(20°C)prior to shell cross-linking with the DVS reagent at pH12for5-6h.
For all three triblock copolymers,the pH of the SCL micellar solutions was adjusted from pH12to approximately pH9after DVS cross-linking in order to minimize any unwanted alkaline hydrolysis of the triblock copolymer.
Synthesis of Gold Nanoparticles Using SCL Micelles as Nanoreactors.Aqueous SCL micellar solutions of PEO-GMA-DEA triblocks(0.1-5.0%w/v)were mixed with aqueous solutions of HAuCl4at various HAuCl4/DEA stoichiometries.After stirring these light yellow solutions for1h,an aqueous solution of excess sodium borohydride was added.The solutions immediately turned wine red,indicating the formation of colloidal gold.
Characterization.Molecular weights and molecular weight distributions were determined by THF GPC using a Viscotek instrument.The setup comprised a PLgel3μm MIXED-E300×7.5mm column,poly(methyl methacrylate)(PMMA)calibration
standards,and a refractive index detector.Transmission electron microscopy(TEM)images were recorded using a Hitachi7100 microscope.Samples were prepared by dipping a Formvar-coated copper grid into an aqueous solution of SCL micelles,followed by air-drying at ambient temperature.All1H NMR spectra were recorded on1.0%w/v copolymer solutions in D2O using a Bruker Avance DPX300MHz spectrometer.
Dynamic light scattering(DLS)studies were performed on a Brookhaven Instruments Corp.BI-200SM goniometer equipped with a BI-9000AT digital correlator using a solid-state laser(125 mW,λ)532nm)at a fixed scattering angle of90°.The intensity-average hydrodynamic diameter,?D h?,and polydispersity(μ2/Γ2) were calculated for each micellar solution before and after cross-linking by cumulants analysis of the experimental correlation function.25,26
The particle size distributions of the SCL micelles were also assessed using a Polymer Laboratories Particle Size Distribution Analyzer(PL-PSDA).This instrument uses the principle of packed column hydrodynamic chromatography(HDC)to frac-tionate particles according to their hydrodynamic volume.This technique is similar in some respects to GPC,except that the packed bed comprises nonporous beads and separation takes place in the channels between the beads.HDC is a relative technique,and the conversion from elution time to particle size involves calibration using a series of near-monodisperse poly-styrene latexes(ex.Duke Scientific)as standards.A type I cartridge,with a nominal operating range of5-300nm,was selected,and the eluent flow rate was2.0mL min-1.Shell cross-linked micellar solutions of2.0-2.5%w/v at either pH3or10 were filtered through a0.45μm Whatman filter prior to analysis, and the sample injection volume was20μL.
Results and Discussion Background.DEA homopolymer is a weak polybase with a p K a of about7.3.27It is water-insoluble at neutral or alkaline pH.Below pH7.0,it is soluble as a weak cationic polyelectrolyte due to protonation of its tertiary amine groups.In contrast,both PEO and GMA homopolymers are water-soluble over a wide pH range.HEMA ho-mopolymer is usually considered to be a water-swellable polymer,rather than water-soluble polymer.13However, we have recently shown that,for a sufficiently low mean degree of polymerization(Dp<50),HEMA homopolymers are water-soluble and exhibit inverse temperature solu-bility behavior.24
pH-Induced Formation of Three-Layer“Onion”Micelles.Both PEO-GMA-DEA triblock copolymers could be molecularly dissolved at acidic pH;on addition of NaOH,micellization occurred above pH7-8,as indicated by the bluish color that is characteristic of micellar solutions.Above pH8,DLS studies revealed a unimodal population corresponding to near-monodisperse micelles.On the basis of chemical intuition,these micelles are expected to have a three-layer onion structure,with the DEA block occupying the micelle core and the GMA and PEO blocks forming the inner shell and corona, respectively.Table2lists the intensity-average hydro-dynamic diameters,?D h?,and polydispersities(μ2/Γ2)of the micelles.The PEO45-GMA40-DEA55triblock formed micelles with a?D h?of21nm,while the PEO45-GMA25-DEA70triblock formed somewhat larger micelles with a ?D h?of35nm.As described in the Experimental Section,
molecular dissolution of the PEO-HEMA-DEA triblock could be achieved only at5°C,and thus a“low temper-ature”route was adopted to prepare SCL micelles using this particular triblock copolymer.
Figure3a,b depicts the NMR spectra recorded for the PEO45-GMA40-DEA55triblock copolymer at different solution pHs.At pH2,the copolymer chains are fully solvated and all the signals expected for each block are visible.At pH8.5,the signals due to the deprotonated DEA block atδ1.3andδ4.2completely disappeared, while the signals from PEO and GMA residues are still evident,indicating the formation of DEA-core micelles with an inner layer comprising hydrophilic GMA residues and an outer corona of PEO chains.
Shell Cross-Linked Micelles with pH-Responsive Cores.DVS has been widely used to cross-link hydroxy-containing polymers to prepare gels,microgels,and nanoparticle networks in alkaline solutions(around pH 12or higher)according to Figure1a.18-22This is an example of Michael addition chemistry,so in principle no byproducts should be generated.However,in practice DVS is hydrolyzed by water(slowly at neutral pH and more rapidly in alkaline solution;see Figure1b).Fortunately,
(24)Weaver,J.V.M.;Bannister,I.;Robinson,K.L.;Armes,S.P. Manuscript in preparation.
(25)Chu,https://www.doczj.com/doc/822959411.html,ser Light Scattering;Academic Press:New York, 1974.
(26)Berne,B.J.;Pecora,R.Dynamic Light Scattering;Plenum Press:New York,1976.
(27)(a)Bu¨tu¨n,V.;Billingham,N.C.;Armes,https://www.doczj.com/doc/822959411.html,mun. 1997,671.(b)Lee, A.S.;Gast, A.P.;Butun,V.;Armes,S.P. Macromolecules1999,32,4302.(c)Butun,V.;Armes,S.P.;Billingham, N.C.Polymer2001,42,5993.(d)Vamvakaki,M.;Billingham,N.C.; Armes,S.P.Macromolecules1999,32,2088.
Table2.Hydrodynamic Diameter,?D h?,and Polydispersity,μ2/Γ2,of Micelles and SCL Micelles Prepared from PEO-GMA-DEA and PEO-GMA-DEA Triblock Copolymers at1.0%w/v
sample code micelle diameter
at pH12(nm)μ2/Γ2
diameter of SCL
micelles at pH12(nm)μ2/Γ2
diameter of SCL
micelles at pH2(nm)μ2/Γ2
PEO45-GMA40-DEA55a210.05210.10310.20 PEO45-GMA25-DEA70a350.15360.17620.26 PEO45-HEMA30-DEA50b300.09310.04420.24
a At a[DVS]/[GMA]molar ratio of0.50.
b At a[DVS]/[HEMA]molar ratio of1.00.
pH-Responsive Shell Cross-Linked Micelles Langmuir,Vol.18,No.22,20028353
DVS reacts more readily with the hydroxy groups on the GMA (or HEMA)residues.It is also likely that the relatively high local concentration of hydroxy groups within the inner shell of the micelles is beneficial in aiding the reaction with the DVS.One advantage of using DVS as the cross-linker is that,in principle,the extent of incorporation of the DVS can be assessed by sulfur microanalyses.
SCL micelles were readily obtained by adding DVS to aqueous solutions of the triblock copolymer micelles at pH 12and ambient temperature.For SCL micelles prepared from a 1.0%w/v aqueous solution of PEO 45-GMA 40-DEA 55at a [DVS]/[GMA]molar ratio of 0.50relative to the primary hydroxy groups ([DVS]/[GMA])0.5),DLS studies indicated a ?D h ?of 21nm at pH 12,which is very similar to the micelle diameter prior to cross-linking.This confirmed the expected intramicellar cross-linking mechanism.The solution pH was then adjusted to pH 2using HCl.If no shell cross-linking had occurred,micellar dissociation into individual triblock copolymer chains would be expected,since the DEA core block becomes soluble under these conditions.DLS studies of the SCL micellar solutions at pH 2revealed a ?D h ?of 31nm with comparable scattering intensity to that observed at pH 12,indicating that cross-linking had been successful.The increase in ?D h ?for the SCL micelles at pH 2compared to pH 12corresponded to a 3-fold increase in volume.This is due to protonation of the DEA chains in the micellar cores at low pH.The cationic charge density makes the DEA chains hydrophilic and mutually repulsive,leading to micellar swelling.For SCL micelles prepared from the PEO 45-GMA 25-DEA 70triblock copolymer under similar conditions,the ?D h ?increased from 36to 62nm,corre-sponding to a 5-fold increase in hydrodynamic volume.This increased degree of swelling can be attributed to the longer core-forming DEA block.Returning to Figure 3,spectra c and d show the 1H NMR spectra recorded for PEO 45-GMA 40-DEA 55SCL micelles at pH 12and at pH 2,respectively.The reappearance of signals assigned to the (protonated)DEA residues at pH 2at δ1.3and δ4.2confirms that the SCL micelle cores become hydrophilic,as expected.
For SCL micelles prepared from PEO -HEMA -DEA triblock copolymers,it was found that the [DVS]/[HEMA]molar ratio should be at least 1.00to ensure covalent stabilization of the micellar structure.In contrast,it was much easier to cross-link the PEO -GMA -DEA triblock copolymer micelles.This is perhaps due to the higher local density of hydroxy groups on the GMA blocks.Moreover,some difference between GMA and HEMA residues might be expected in their reactivity toward DVS,that is,the hydroxy groups on GMA are more nucleophilic due to the electron-withdrawing effect of the adjacent hydroxy groups.The results obtained for the PEO 45-HEMA 30
-
Figure 3.1H NMR spectra of the PEO 45-b -GMA 40-b -DEA 55triblock copolymer:(a)at pH 2;(b)at pH 8.5;(c)after cross-linking at a [DVS]/[GMA]molar ratio of 0.50at pH 12;(d)at pH 2after shell cross-linking.
8354Langmuir,Vol.18,No.22,2002Liu et al.
DEA 50triblock are summarized in Table 2.Before shell cross-linking,these micelles had a mean diameter of 30nm with a μ2/Γ2of 0.09.After cross-linking at a [DVS]/[HEMA]molar ratio of 1.00,the resulting SCL micelles had a mean diameter of 31nm at pH 12.On addition of acid (pH 2),the micelles swell considerably to 42nm,which corresponds to a 2.5-fold increase in hydrodynamic volume.Since the side products of the hydrolysis of DVS in alkaline media are water-soluble (see Figure 1b),the SCL micelles were purified by dialysis after the cross-linking reaction.Sulfur microanalyses were then utilized to assess the DVS content of the SCL micelles,which is related to the degree of cross-linking.After purification by dialysis,the sulfur content (normalized to nitrogen)of SCL micelles prepared from the PEO 45-GMA 25-DEA 70triblock indi-cated a DVS/GMA molar ratio of 0.75,as compared to an initial molar ratio of 1.00.This reduction is attributed to the loss of physically occluded DVS (and/or its water-soluble side products)from the SCL micelles.Dialysis also results in the disappearance of the sharp signal at δ3.9observed in the NMR spectrum (see Figure 3d),which indicates that this feature is due to hydrolyzed side products of DVS.Similar results were obtained for the PEO -HEMA -DEA triblock,except that a much lower DVS/HEMA molar ratio of 0.125was obtained,compared to an initial molar ratio of 1.00.This is believed to be related to the relatively low reactivity of DVS with the HEMA residues compared to the GMA residues.
Figure 4shows the relationship between ?D h ?and the [DVS]/[GMA]molar ratio for selected SCL micelles at pH 12and pH 2.Before cross-linking,the PEO 45-GMA 40-DEA 55micelles prepared at 2.5%w/v had a hydrodynamic diameter of 22nm.The ?D h ?of SCL micelles at pH 12is little changed from that of the non-cross-linked precursor micelles and remains almost constant as the [DVS]/[GMA]molar ratio is varied from 0.125to 0.75.Within this range of molar ratios,the ?D h ?of the SCL micelles at pH 2is always larger than that at pH 12,as expected.A [DVS]/[GMA]molar ratio as low as 0.125is enough to covalently stabilize the micellar structure.The most marked pH-induced swelling behavior for SCL micelles was observed at a [DVS]/[GMA]molar ratio of 0.25.At higher [DVS]/[GMA]molar ratios,less swelling is observed,because the DEA chains in the micelle core are more constrained by the more heavily cross-linked GMA residues in the inner shell.
Further DLS studies of SCL micelles indicated that most of the pH-induced swelling occurred at around pH 7-8,which is consistent with the known p K a value for the DEA block.27This augurs well for the potential application of
such SCL micelles as nanosized drug delivery vehicles,since the abrupt change in hydrophilicity of the DEA cores (and concomitant increased permeability of the GMA cross-linked layer)is expected to allow “triggered release”of hydrophobic drugs.
Figure 5shows the aqueous electrophoresis data obtained for SCL micelles prepared from the PEO 45-GMA 40-DEA 55triblock copolymer at a [DVS]/[GMA]molar ratio of 0.25.Only relatively small changes in zeta potential (from -6to +10mV)were observed when the solution pH was decreased from pH 12to pH 2,with an isoelectric point occurring at around pH 7.0-7.5.This relatively weak electrophoretic response is consistent with the neutral PEO chains being located in the micelle corona.It seems that most of the hydrophilic,protonated DEA chains remain inside the SCL micelle cores even at pH 2,although we cannot rule out (partial)migration of the cationic DEA chains through the cross-linked GMA layer to form a “mixed”corona with the neutral PEO chains.
A new commercial particle size analyzer,the PL-PSDA (ex.Polymer Laboratories),was used to assess the effect of pH on the particle size distributions of SCL micelles prepared from the PEO 45-GMA 40-DEA 55triblock co-polymer at a concentration of 2.5%w/v (see Figure 6).At pH 10,the particle size distribution ranged from 10to 40nm.The mean volume-average diameter was calculated to be 21nm,which is very close to the intensity-average diameter ?D h ?of 22nm obtained from DLS.Figure 5also shows the particle size distribution of the same SCL micelles at pH 3.The shift in the particle size distribution is evident,and the volume-average diameter of SCL micelles at pH 3is 26nm.Bearing in mind the
different
Figure 4.Relationship between ?D h ?and [DVS]/[GMA]initial molar ratio for SCL micelles prepared from the PEO 45-GMA 40-DEA 55copolymer at 2.5%w/v at both pH 2(hydrated micelle cores)and pH 12(dehydrated micelle
cores).
Figure 5.Zeta potential versus solution pH for SCL micelles prepared from the PEO 45-GMA 40-DEA 55copolymer at 2.5%w/v at a [DVS]/[GMA]molar ratio of
0.25.
Figure 6.Typical volume-average particle size distribution curves at pH 10and pH 3obtained using the PL-PSDA instrument for SCL micelles prepared from the PEO 45-GMA 40-DEA 55triblock at 2.5%w/v at a [DVS]/[GMA]molar ratio of 0.25.
pH-Responsive Shell Cross-Linked Micelles Langmuir,Vol.18,No.22,20028355
moments of the size distribution measured by DLS and the PSDA,this value compares well to the?D h?of29nm obtained from DLS.The increase in volume-average particle diameter relative to that obtained at pH10again clearly indicates significant swelling of the SCL micelles. As far as we are aware,this is the first time that the PL-PSDA technique has been applied to SCL micelles. Advantages of this sizing technique include the follow-ing:(i)peak-to-peak resolution is much better compared to that for DLS;(ii)typical analysis times are less than 10min;(iii)many samples can be run sequentially using the auto-sampler mode;(iv)the reported volume-average particle diameter is likely to be more comparable to that observed by electron microscopy;(v)no knowledge of the particle density is required.On the other hand,careful calibration is required and,as in DLS,aqueous solutions should be ultrafiltered prior to use.On balance,we believe that the PL-PSDA instrument is a useful new charac-terization tool for SCL micelles,and we intend to exploit this technique further in future studies.
Preparation of Gold Colloids Using SCL Micelles as Nanoreactors.Recently there has been a great deal of interest in the synthesis of metal or semiconductor nanoparticles because of their unique size-dependent chemical and physical properties,which makes them ideal candidates for electronic and optical nanodevices.28-32In particular,polymer-coated metal or semiconductor nano-particles exhibit increased colloid stability,enhanced protection against oxidation,and much higher catalytic activity.33,34
In the present study,we have found that the cores of the SCL micelles can be selectively loaded with AuCl4-ions simply by using HAuCl4to protonate the basic DEA residues.In situ chemical reduction of the Au(III)with NaBH4leads to elemental gold nanoparticles confined within the SCL micelles,which act as nanoreactors.The reduction of Au(III)to Au(0)can be conveniently followed by UV-visible absorption spectroscopy.35Figure7depicts UV-visible spectra recorded for(a)dilute aqueous solu-tions of SCL micelles(?D h?)prepared from the PEO45-GMA25-DEA70triblock copolymer,(b)the same SCL
micelles loaded with HAuCl4,and(c,d)two gold-loaded SCL micelles obtained after NaBH4reduction at different HAuCl4/DEA molar ratios.The precursor SCL micelles exhibited an absorption peak at278nm.After loading with HAuCl4,the micellar solution became light yellow and an absorption band was observed at316nm,as expected.36After NaBH4reduction,this solution turned wine red.The absorption peak at316nm was replaced with a broad absorption envelope in the400-600nm range,which was assigned to the surface plasmon resonance band of gold nanoparticles.36Theλmax of this plasmon band increased from499to508nm as the HAuCl4/ DEA molar ratio increased from0.2to0.4.This indicates that the mean size of the gold nanoparticles is around 1-5nm and increased at higher HAuCl4loadings.No changes in the visible absorption spectra were observed after storage for4months,suggesting high chemical and colloidal stability for these gold-loaded SCL micelles. Figure8shows a typical TEM image obtained for SCL micelles at pH4.Approximately spherical micelles with a mean diameter of around45nm are observed;this is in reasonable agreement with the DLS diameter of62nm if solvation and polydispersity effects are taken into account.For gold-loaded SCL micelles synthesized at a HAuCl4/DEA molar ratio of0.40,further TEM studies (not shown)suggest that gold nanoparticles are mainly located inside the SCL micelles.Each SCL micelle appears to act as a nanoreactor for the synthesis of gold colloids, and there are many gold nanoparticles inside each SCL micelle.This is understandable given the very fast rate of reduction achieved using NaBH4at neutral pH.37The mean TEM diameter of the gold nanoparticles is of the order of several nanometers,which is consistent with the plasmon absorption peak observed at508nm.36
There are several advantages to using SCL micelles prepared from the PEO-GMA-DEA triblock copolymer for the synthesis of gold nanoparticles.First,this hydro-philic,functional triblock is readily synthesized using ATRP without requiring protecting group chemistry. Second,in this particular case the shell cross-linking is
(28)Alivisatos,S.Science1995,268,1728.
(29)Fo¨rster,M.;Antonietti,M.Adv.Mater.1998,10,195.
(30)Bronstein,L.M.;Sidorov,S.N.;Valetsky,P.M.;Hartmann,J.; Co¨lfen,H.;Antonietti,https://www.doczj.com/doc/822959411.html,ngmuir1999,15,6256.
(31)Caruso,F.;Shi,X.;Caruso,R.A.;Susha,A.Adv.Mater.2001, 13,740.
(32)Gro¨hn,F.;Bauer,B.J.;Akpalu,Y.A.;Jackson,C.L.;Amis,A. J.Macromolecules2000,33,6042.
(33)Klingelho¨fer,S.;Heitz,W.;Greiner,A.;Oestreich,S.;Fo¨rster, S.;Antonietti,M.J.Am.Chem.Soc.1997,119,10116.
(34)Qi,L.;Co¨lfen,H.;Antonietti,M.Nano Lett.2001,1,61.
(35)Wilcoxon,J.P.;Williamson,R.L.;Baughman,R.J.Chem.Phys.
1993,98,9933.
(36)Chen,W.;Cai,W.;Zhang,Z.;Zhang,L.Chem.Lett.2001,152.
(37)Antonietti,M.;Gro¨hn,F.;Hartmann,J.;Bronstein,L.Angew. Chem.,Int.Ed.Engl.1997,36,
2080.
Figure7.UV-visible spectra of SCL micelles prepared from PEO45-GMA25-DEA70triblock copolymers at2.5%w/v and pH12at a[DVS]/[GMA]molar ratio of0.50:(a)at pH7.5prior to loading with HAuCl4;(b)at pH3after loading with HAuCl4 at an HAuCl4/DEA molar ratio of0.20;(c)after reduction with NaBH4at the same HAuCl4/DEA molar ratio;(d)after reduction at an HAuCl4/DEA molar ratio of
0.40.
Figure8.Typical TEM image of SCL micelles prepared from the PEO45-GMA25-DEA70triblock at2.5%w/v at a[DVS]/ [GMA]molar ratio of0.50.
8356Langmuir,Vol.18,No.22,2002Liu et al.
essential to preserve the nanoreactor dimensions,since the conventional non-cross-linked micelles would dissoci-ate immediately on addition of the acidic HAuCl4solution (due to protonation of the DEA block).Third,in our most recent experiments we have shown that the shell cross-linking chemistry,the HAuCl4loading,and the in situ reduction can be carried out at relatively high solids(5% w/v)with the resulting gold-loaded SCL micelles retaining good colloid stability.In principle,much higher concen-trations could be employed without risking deformation of the spherical morphology of the SCL micelles.
Conclusions
Novel well-defined PEO-GMA-DEA and PEO-HEMA-DEA triblock copolymers were successfully syn-thesized by ATRP using a PEO-based macroinitiator. These triblock copolymers dissolved molecularly in aque-ous solution at low pH;on addition of NaOH,combined DLS and1H NMR studies confirmed that micellization occurred at around pH7-8to form three-layer onionlike micelles comprising DEA cores,GMA(or HEMA)inner shells,and PEO coronas.Selective cross-linking of the GMA(or HEMA)residues was achieved by adding divinyl sulfone to alkaline micellar solutions at room temperature. The resulting SCL micelles exhibited reversible swelling behavior on varying the solution pH.At low pH,the DEA cores become protonated and hence hydrophilic.The effect of varying the block compositions and the[DVS]/[GMA] molar ratio on the structural stability and pH-dependent (de)swelling of the SCL micelles was studied in some detail. These SCL micelles can act as nanoreactors:loading the DEA cores with HAuCl4,followed by reduction with NaBH4,produced gold nanoparticles within the interior of the micelles.
Acknowledgment.EPSRC is acknowledged for post-doctoral grants to support S.L.(GR/N17409)and M.S. (GR/M47553).J.V.M.W.acknowledges an EPSRC Ph.D. studentship and thanks Laporte Performance Chemicals (Hythe,U.K.)for generous CASE support.
LA020496T
pH-Responsive Shell Cross-Linked Micelles Langmuir,Vol.18,No.22,20028357
电脑启动过程详解 1.当按下电源开关时,电源就开始向主板和其它设备供电,这时电压还不太稳定,主板上的控制芯片组会向CPU发生并保持一个RESET(重置)信号,让CPU内部自动恢复到初始状态,但CPU在些刻不会马上执行指令,当芯片组检查到电源已经开始稳定供电了(当然从不稳定,到稳定的过程只是一瞬间的事情)它便撤去RESET信号(如果是手工按下电脑面板上的RESET按钮来重启机器,那么松开该按钮时芯片组就会撤去RESET信号)CPU马上从地址FFFF0H处开始执行指令,这个地址实际在系统BIOS的地址范围内, 无论是Award BIOS,还是AMI BIOS,在这里的只是一条跳转指令,跳到系统BIOS中真正的启动代码处。 2.系统BIOS的启动代码首先要做的事情就进行POST(Power-On Self Test,加电后自检),POST的主要任务是检查系统中一些关键设备是否存在和是否正常工作,例如内存和显卡等设备.由于POST是最早进行的检查过程,此时显卡还没有初始化,如果系统BIOS在进行POST的过程中发现了些致命错误,例如没有找到内存或内存有问题 (此时只会检查640KB常规内存),那么系统BIOS就会直接控制嗽叭发生声音来报告错误,声音的长短和次数代表了错误的类型.在正常情况下,POST过程进行的非常快,我们几乎无法感觉到它的存在,POST结束之后就会调用其它代码来进行更完整的硬件检测。 3.接下来系统BIOS将查找显卡的BIOS,前面说过,存放显卡BIOS的ROM芯片的超始地址通常设在 C0000H,系统BIOS在这个地方找到显卡BIOS之后就调用它的初始化代码来初始化显卡,此时多数显卡都在屏幕上显示出一些初始化信息,介绍生产厂商,图形芯片类型等内容,不过这个画面几乎是一闪而过,系统BIOS接着会查找其它设备的BIOS程序,找到之后同样会调用这些BIOS内部的初始化代码来初始化相关的设备。 4.查找完所有其它设备的BIOS之后,系统BIOS将显示出它自己的启动画面,其中包括有系统BISO的类型,序列号和版本号等内容. 5.接着系统BIOS将检查和显示CPU的类型和工作频率,然后开始测试所有RAM,并同时在屏莫显示内存测试的速度,用户可以在CMOS设置中自行决定使用简单耗时少或详细耗时多的测试方式. 6.内存测试通过之后,系统BIOS将开始检测系统中安装的一些标准硬件设备,包括硬盘,CD-ROM,串口,并口,软驱等设备,另外绝大数较新版本的系统BIOS在这一过程中还要自动检测和设置内存的定时参数,硬盘参数和访问模式等. 7.标准设备检查完毕后,系统BIOS内部的支持即插即用的代码将开始检测和配置系统中安装的的即插即用设备,每找到一个设备之后,系统BIOS都会在屏幕上显示出设备的名称和型号等信息,同时为该设备分配中断,DMA通道和I/O端口等资源。 8.到这一步为止,所有硬件都已经检测配置完毕了,多数系统BIOS会重新清屏并在屏幕上方显示出一个表格,其它概略地列出了系统中安装的各种标准硬件设备,以及它们使用的资源和一些相关工作参数。 9.接下来系统BIOS会更新ESCD(Extended system configuration data,扩展系统配置数据.)ESCD是系统BIOS用来与操作系统交换硬件配置信息的一种手段,这些数据被存放在CMOS之中,通常ESCD数据只在系统配置发生改变后才会更新,所以不是每次启动电脑时都能够看到"updata ESCD … Success"这样的信息, 不过某些主板的系统BIOS在保存ESCD数据时使用了与widnwos 9x不相同的数据格式,于是widnwos 9x在启动过程中会把ESCD数据修改成自己的格式,但在下一次启动时,既使硬件配置没有发生改变,系统BIOS也会把ESCD的数据格式修改回来,如此循环,将会导致在每次启动电脑时,系统BIOS都要更新一遍ESCD,这就是为什么有些机器在每次启动时都会显示出相关信息的原因。 10.ESCD更新完毕后,系统BIOS的启动代码将进行它的最后一项工作,即根据用户指定的启动顺序从软件,硬件或光驱启动,以从C盘启动为例,系统BIOS将读取并执行硬盘上的主引导记录,主引导记录接着从分区表中找到第一个活动分区,然后读取并执行这个活动分区的引导记录,而分区引导记录将负责读取并执行 IO.SYS这是DOS和widnows 9x的IO.SYS(或NT的NTLDR)首先要初始化一些重要的系统数据,然后将显示出我们熟悉的蓝天白云,在这幅画面之下,widnwos 将继续进行DOS部分和GUI(图形用户界面)部分的引导和初始化工作. 上面介绍的便是电脑在打开电源开关(或按RESET)进行冷启动时所要完成的各种初始化工作,如果在DOS 下按Ctrl Alt DEL组合键,(或从windows中选择重新启动电脑)来进行热启动,那么POST过程将被跳过去,
小学英语语法大全 第1讲字母 1、英语中共有26个字母。Aa，Ee，Ii，Oo，Uu是元音字母，Yy是半元音字母，其余是辅音字母。英语单词就是由这26个字母组合而成的。Aa和Ii可以独立成词，分别表示“一个（张……）”和“我”的意思，Ii翻译成“我”时要大写。 2、英语字母可以分为印刷体和书写体。在书、报、杂志上见到的一般都是印刷体。在四线三格上书写时应注意书写位置，可以记住以下口诀：大写字母不顶格，小写字母占满格。书写时还要注意字母的笔顺。 3、英语句子的第一个单词的首字母要大写。单词与单词之间在书写时必须保持适当的距离，一般以空出一个小写字母的宽度为宜。句子的末尾要有标点符号。 4、英语中的句号是一个实心圆点(.)，省略号是三个居下的实心圆点（…），英语中没有顿号和书名号，顿号用逗号替代，书名用斜体字表示。 5、英语缩写词 PRC中华人民共和国UN 联合国 WHO 世界卫生组织NBA美国职业篮球联赛KFC 肯德基 IT 信息技术 EQ 情商 CCTV 中国中央电视台kg 千克 a.m. 上午USA 美国 HK 香港 WTO 世界贸易组织 CBA 中国男子篮球联赛 ATM 自动柜员机 ID 身份证 CPU 中央处理器 BBC 英国广播公司 cm 厘米 p.m. 下午 UK 英国 SOS 国际求救信号 UFO 不明飞行物 VIP 贵宾 EMS邮政特快专递 IQ 智商 RMB 人民币 VOA 美国之音 No. 号码 6
第2讲语音 1、音素：语音的最小单位。 2、元音：发音时气流不受阻碍。元音分为单元音和双元音两类。 单元音发音时唇形和舌位不变；双元音发音时由一个元音向另一个 元音滑动，唇形和舌位有一个变化过程，且前重后轻，前长后短。 3、辅音：发音时气流受到阻碍。辅音分为清辅音和浊辅音两类。 清辅音发音时声带不振动；浊辅音发音时声带振动。 4、音标：用来记录音素的符号。为了避免与字母混淆，音标被放在斜括号/ /内。 5、英语中的一个字母或字母组合在不同的单词中发音可能是不一样的，而相同的发音对应的字母或字母组合也可能不完全相同。 6、开音节：以元音字母结尾或以一个元音字母加一个辅音字母再加不发音的e结尾 （r除外）的音节。元音字母在开音节中读长音，即该字母的名称音。 闭音节：以一个或几个辅音字母（r除外）结尾。元音字母在闭音节中读短音。
六年级语法总复习 一、词汇 （一）一般过去时态 一般过去时态表示在过去的某个时间发生的动作或存在的状态，常和表示过去的时间状语连用。例如yesterday, last weekend ,last Saturday ,等连用。基本句型：主语+动词的过去式+其他。例句——What did you do last weekend?你上周做什么了？ ——I played football last weekend.我踢足球了。 ★规则动词过去式的构成 ⒈一般在动词原形末尾加-ed。例如：play—played ⒉词尾是e的动词直接加-d。例如：dance—danced ⒊末尾只有一个辅音字母的重读闭音节词，先双写这个辅音字母，再加-ed。例如stop（停止）--stopped ⒋结尾是“辅音字母+y”的动词，变“y”为“i”，再加-ed，例如：study--studied ★一些不规则变化的动词过去式 am/is—was are—were go—went swim—swam fly—flew do—did have—had say—said see—saw take—took come—came become—became get—got draw—drew hurt—hurt read—read tell—told will—would eat—ate take—took make—made drink—drank sleep(睡觉)—slept cut（切）--cut sit(坐)—sat begin(开始)—began think—thought find—found run(跑)---ran buy—bought win—won give(给)—gave sing—sang leave—left hear（听）--heart wear—wore （二）一般现在时态 一般现在时态表示包括现在时间在内的一段时间内经常发生的动作或存在的状态，表示习惯性或客观存在的事实和真理。常与often ,always ,usually ,sometimes ,every day等连用。基本句型分为两种情况： ●主语（非第三人称）+动词原形+其他。例句：——What do you usually do on the weekend?——I usually do my homework on the weekend. ●主语（第三人称）+动词的第三人称单数形式+其他。例句： ——What does Sarah usually do on the weekend?萨拉通常在周末干什么？ ——She usually does her homework on the weekend.她通常在周末做她的家庭作业。 ★动词第三人称单数形式的变化规则 ⒈一般直接在动词词尾加-s.例如：play—plays ⒉以s ,x ,ch,sh结尾的动词加-es。例如：watch—watches ⒊以辅音字母加y结尾的动词，变y为i，再加es,例如：fly—flies ⒋个别不规则变化动词，需单独记忆，例如：do—does go—goes （三）现在进行时态 现在进行时态表示说话人现在正在进行的动作。基本句型：主语+be+动词的-ing+其他。 例如:——What are you doing ?你在干什么？ ——I am doing my homework..我正在做作业。 ★动词现在分词的变化规则 ⒈一般直接在词尾加ing ，例如;wash—washing ⒉以不发音e字母结尾的动词，去掉e ,再加ing.例如：make—making ⒊末尾只有一个辅音字母的重读闭音节词，要双写最后一个辅音字母再加ing.例如swim—swimming （四）一般将来时态 一般将来时态表示将来某一时间或某一段时间内发生的动作或存在的状态。常与表示将来的时间如tomorrow ,next weeken ,this afternoon 等连用。我们通常用will,be going to+动词原形来表示一般将来时态。
从打开电源到开始操作，计算机的启动是一个非常复杂的过程。 零、boot 的含义 先问一个问题，"启动"用英语怎么说？ 回答是boot。可是，boot 原来的意思是靴子，"启动"与靴子有什么关系呢？原来，这里的boot 是bootstrap（鞋带）的缩写，它来自一句谚语： "pull oneself up by one's bootstraps" 字面意思是"拽着鞋带把自己拉起来"，这当然是不可能的事情。最早的时候，工程师们用它来比喻，计算机启动是一个很矛盾的过程：必须先运行程序，然后计算机才能启动，但是计算机不启动就无法运行程序！ 早期真的是这样，必须想尽各种办法，把一小段程序装进内存，然后计算机才能正常运行。所以，工程师们把这个过程叫做"拉鞋带"，久而久之就简称为boot 了。 计算机的整个启动过程分成四个阶段。 一、第一阶段：BIOS 上个世纪70 年代初，"只读内存"（read-only memory，缩写为ROM）发明，开机程序被刷入ROM 芯片，计算机通电后，第一件事就是读取它。 这块芯片里的程序叫做"基本輸出輸入系統"（Basic 无效/Output System），简称为BIOS。1. 1 硬件自检 BIOS 程序首先检查，计算机硬件能否满足运行的基本条件，这叫做"硬件自检"（Power-On Self-Test），缩写为POST。 如果硬件出现问题，主板会发出不同含义的蜂鸣，启动中止。如果没有问题，屏幕就会显示出CPU、内存、硬盘等信息。 1. 2 启动顺序 硬件自检完成后，BIOS 把控制权转交给下一阶段的启动程序。 这时，BIOS 需要知道，"下一阶段的启动程序"具体存放在哪一个设备。也就是说，BIOS 需要有一个外部储存设备的排序，排在前面的设备就是优先转交控制权的设备。这种排序叫做"启动顺序"（Boot Sequence）。 打开BIOS 的操作界面，里面有一项就是"设定启动顺序"。 二、第二阶段：主引导记录 BIOS 按照"启动顺序"，把控制权转交给排在第一位的储存设备。 这时，计算机读取该设备的第一个扇区，也就是读取最前面的512 个字节。如果这512 个字节的最后两个字节是0x55 和0xAA，表明这个设备可以用于启动；如果不是，表明设备不能用于启动，控制权于是被转交给"启动顺序"中的下一个设备。 这最前面的512 个字节，就叫做"主引导记录"（Master boot record，缩写为MBR）。 2. 1 主引导记录的结构 "主引导记录"只有512 个字节，放不了太多东西。它的主要作用是，告诉计算机到硬盘的哪一个位置去找操作系统。 主引导记录由三个部分组成： （1）第1-446 字节：调用操作系统的机器码。 （2）第447-510 字节：分区表（Partition table）。 （3）第511-512 字节：主引导记录签名（0x55 和0xAA）。 其中，第二部分"分区表"的作用，是将硬盘分成若干个区。 2. 2 分区表 硬盘分区有很多好处。考虑到每个区可以安装不同的操作系统，"主引导记录"因此必须知道将控制权转交给哪个区。
小学英语语法大全经典全面 第2讲语音 1、音素：语音的最小单位。 英语中共有48个音素，其中元音音素20个，辅音音素28个。 /i:/,/?/,/?:/,/?/,/ɑ:/,//,/?:/,/?/ ,/u:/,/?/,/e/,/?/ /p/,/t/,/k/,/t/,/tr/,/ts/,/f/,/θ/,/s/,/ ∫/,/h/ 2、元音：发音时气流不受阻碍。元音分为单元音和双元音两类。 单元音发音时唇形和舌位不变；双元音发音时由一个元音向另 一个 元音滑动，唇形和舌位有一个变化过程，且前重后轻，前长后 短。
3、辅音：发音时气流受到阻碍。辅音分为清辅音和浊辅音两类。 清辅音发音时声带不振动；浊辅音发音时声带振动。 4、音标：用来记录音素的符号。为了避免与字母混淆，音标被放在斜括号/ /内。 5、英语中的一个字母或字母组合在不同的单词中发音可能是不一样的， 而相同的 发音对应的字母或字母组合也可能不完全相同。 6、开音节：以元音字母结尾或以一个元音字母加一个辅音字母再加不发 音的e结尾（r除外）的音节。元音字母在开音节中读长音， 即该字母的名称音。 闭音节：以一个或几个辅音字母（r除外）结尾。元音字母在闭音节中读短音。 // cup 第3讲名词 名词是指表示人和事物名称的词，可以分为专有名词和普通名词两大类。
1、专有名词：特定的人、地方、机构等专有的名称。第一个字母通常要大写。 . Jim Green， New York， Bank of China，Peking University 星期、月份、节日、学科、报刊名也是专有名词。 . Monday，May，Christmas，Spring Festival，Maths，China Daily 2、普通名词：表示一类人或物或抽象概念的名称。普通名词又可以分为四类: 个体名词——表示某类人或东西中的个体，如：student , desk 集体名词——表示若干个体组成的集合体，如：class , family 物质名词——表示无法分为个体的物质名称，如：water , rice , sand，hair 抽象名词——表示情感，状态，品质等抽象名称，如：love ，carelessness 个体名词和集体名词多数可以用数目来计算，称为可数名词，有单、复数形式； 物质名词和抽象名词通常无法用数目计算，称为不可数名词，一般只有一种形式。
小学英语语法大全经典全面 第1讲字母 第2讲语音 第3讲名词 第4讲冠词 第5讲代词 第6讲形容词 第7讲副词 第8讲介词 第9讲数词 第10讲连词 第11讲动词 第12讲一般现在时第13讲现在进行时第14讲一般过去时第15讲一般将来时第16讲句法 第17讲听力 第18讲话题 第19讲构词法 第20讲英美文化常识p.2 p.3 p.4~5 p.6 p.7~8 p.9 p.9 p.10~11 p.12 p.13 p.14 p.15 p.16 p.17 p.18 p.19~20 p.21 p.22~24 p.25 p.26
第1讲字母 1、英语中共有26个字母。Aa，Ee，Ii，Oo，Uu是元音字母，Yy是半元音字母，其余是辅音字母。英语单词就是由这26个字母组合而成的。Aa和Ii可以独立成词，分别表示“一个（张……）”和“我”的意思，Ii翻译成“我”时要大写。 2、英语字母可以分为印刷体和书写体。在书、报、杂志上见到的一般都是印刷体。在四线三格上书写时应注意书写位置，可以记住以下口诀：大写字母不顶格，小写字母占满格。书写时还要注意字母的笔顺。 3、英语句子的第一个单词的首字母要大写。单词与单词之间在书写时必须保持适当的距离，一般以空出一个小写字母的宽度为宜。句子的末尾要有标点符号。 4、英语中的句号是一个实心圆点(.)，省略号是三个居下的实心圆点（…），英语中没有顿号和书名号，顿号用逗号替代，书名用斜体字表示。 5、英语缩写词 PRC中华人民共和国UN 联合国 WHO 世界卫生组织NBA美国职业篮球联赛KFC 肯德基 IT 信息技术 EQ 情商 CCTV 中国中央电视台kg 千克 a.m. 上午USA 美国 HK 香港 WTO 世界贸易组织 CBA 中国男子篮球联赛 ATM 自动柜员机 ID 身份证 CPU 中央处理器 BBC 英国广播公司 cm 厘米 p.m. 下午 UK 英国 SOS 国际求救信号 UFO 不明飞行物 VIP 贵宾 EMS邮政特快专递 IQ 智商 RMB 人民币 VOA 美国之音 No. 号码 6
三年级下册单词、句子Unit1Welcome back to school欢迎回到学校 UK英国 Canada加拿大 USA美国 she[?i?]她 student/'stju:d?nt/学生pupil[?pju?pl] 学生；（特指）小学生he[hi?]他teacher/'ti:t??/教师boy/b?i/男孩and[?nd]和，与girl/g?:l/女孩new[nju?]新的friend/fr end/朋友today[t?'de?]今天 Welcome!欢迎！ Where are you from?你是哪里人？ I’m from the UK.我是英国人 Unit2My family我的家庭 father/'fɑ:e?/父亲 dad/d?d/爸爸 man/m?n/男人woman/'wum?n/女人mother/'m?e?/母亲sister/'sist?/姐妹brother/'br?e?/兄弟grandmother/'gr?n d,m?e?/ （外）祖母gr an dm a/'gr?ndmɑ:/ （口语）（外）祖母grandfather/'gr?nd,fɑ:e?/ （外）祖父 gran dp a/'gr?ndpɑ:/(口语) (外 family['f?m?li]家；家庭)祖父
Who’s that man?那位男士是谁啊？ He’my father.他是我爸爸。 Who’s that woman?那位女士是谁啊？ She’s my mother.她是我妈妈。 Is she your mother?她是你妈妈吗？ Yes,she is.是的，她是。 Is he your father?他是你爸爸吗？ No,he isn’t.不，他不是。 Unit3At the zoo在动物园 thin/θin/瘦的big/big/大的 fat/f?t/胖的giraffe/d?i'rɑ:f/长颈鹿 tall/t?:l/高的so[s??]这么；那么 short/??:t/短的;矮的children儿童 long/l??/长的tail/teil/尾 巴small/sm?:/小的 It’s so tall！它好高啊！ Come here,children!这里来，孩子们！ It has a long nose.它有长鼻子。 It has small eyes and big ears.它有小眼睛和大耳朵。
人教版高中英语必修3 重点词汇、短语、句型、语法大全 Unit1 Festivals around the world 【重点词汇、短语】 1. take place 发生 2. religious 宗教的 3. in memory of 纪念 4. belief 信任，信心，信仰 5. dress up 盛装，打扮 6. trick 诡计，窍门 7. play a trick on 搞恶作剧，诈骗 8. gain 获得 9. gather 搜集，集合 10. award 奖品，授予 11. admire 赞美，钦佩 12. look forward to 期望，盼望 13. day and night 日夜 14. as though 好像 15. have fun with 玩的开心 16. permission 许可，允许
17. turn up 出现，到场 18. keep one’s word 守信用 19. hold one’s breath 屏息 20. apologize道歉 21. obvious 显然的 22. set off 出发，动身，使爆炸 【重点句型】 1. Please make sure when and where the accident took place. 请查清楚事故是何时何地发生的。 2. Some festival are held to honour the dead, or satisfy and please the ancestors, who could return either to help or to do harm. 还有一些节日，是为了纪念死者、满足或取悦祖先，因为（祖先们）有可能回到世上帮助他们，也有可能带来危害。 3. In Japan the festival is called Obon，when people should go to clean the graves and light incense in memory of their ancestors.（非限制性定语从句） 在日本，这个节叫孟兰盆节，在这个节日里，人们要上坟、扫墓、烧香，以缅怀祖先。 4. They dress up and try to frighten people. 他们乔装打扮去吓唬别人。 5. If they are not given anything, the children might play a trick.
PEP 小学英语三年级上册单词、句子、语法、练习汇总 Unit 1第一单元 pencil 铅笔 ruler 尺子 eraser 橡皮 crayon 蜡笔 book 书 bag 书包 pen 钢笔 pencil-box 铅笔盒 sharpener 卷笔刀 open your pencil-box show me your pen close your book carry your bag 打开你的铅笔盒 给我看看你的钢笔 合上你的书 背上你的书包 Hello ! I ’m Chen Jie:你好，我是陈洁. What ‘s your name ?你叫什么名字？ My name ’s Mike.我的名字是Mike. I have a ruler . 我有一把尺子。 ========================================================================== Unit 2第二单元 red 红色的 yellow 黄色的 green 绿色的 blue 蓝色的 purple 紫色的 white 白色的 black 黑色的 orange 橙色的 pink 粉红色的 brown 棕色的 show me ….:给我看… black black orange orange white white brown brown stand up sit down touch the ground turn around 黑色，站起来 橙色，坐下 白色，摸地板 棕色，转圈 Good morning.早上好。 Good afternoon.下午好。 This is Miss Green.这是格林小姐。 I see green.我看见了绿色。 Nice to meet to you.很高兴认识你。 Nice to meet you,too. 也很高兴认识你。
Windows启动过程详解 我们每天都在和Windows打交道，很多人可能每天都要面对多次W indows的启动过程，可是您知道在Windows的启动过程背后，隐藏着什么秘密吗？在这一系列过程中都用到了哪些重要的系统文件？系统的启动分为几个步骤？在这些步骤中计算机中发生了什么事情？这些就是本文试图告诉您的。 本文的适用范围 随着技术的发展，我们能够见到的计算机硬件种类越来越多。以计算机上最重要的组件CPU来说，目前就有很多选择。当然，这里的选择并不是说AMD或者Intel这种产品品牌，而是指其内部的体系结构。目前常见的CPU体系结构主要基于复杂指令集（Complex I nstruction Set Computing，CISC）或者精简指令集（Reduced Ins truction Set Computing，RISC），我们常用的Intel的Pentium、C eleron系列以及AMD的Athlon、Sempron系列都是基于复杂指令集的，而这些基于复杂指令集的CPU还有32位和64位的寄存器数据带宽区别。关于这些指令集以及寄存器数据带宽之间的区别等内容比较繁杂，而且不是本文的重点，感兴趣的朋友可以自己在网上搜索相关内容。因为CPU种类的不同，在不同CPU的系统中运行的Wind ows的启动过程也有一些小的不同。本文将会以目前来说最普遍的，在x86架构的系统上安装的32位Windows XP Professional为例向
您介绍。 基本上，操作系统的引导过程是从计算机通电自检完成之后开始进行的，而这一过程又可以细分为预引导、引导、载入内核、初始化内核，以及登录这五个阶段。 在继续阅读之前，首先请注意图1，这是Windows XP的操作系统结构，其中包括了一些在后台工作的组件以及经常和我们打交道的程序。在了解Windows XP的启动过程之前，对系统结构有一个初步概念是很重要的。
[2] 英语语法术语汇总（中英对照） 英语语法术语（中英对照） 语法 grammar 句法 syntax 词法 morphology 句子 sentence 从句 clause 词组 phrase 词类 part of speech 单词 word 实词 notional word 虚词 structural word 单纯词simple word 派生词derivative 复合词compound 词性 part of speech 名词 noun 专有名词proper noun 普通名词common noun 可数名词count able noun 不可数名词 uncount able noun 抽象名词 abst ract noun
具体名词concret noun 物质名词 mat erial noun 集体名词collective noun 个体名词individual noun 介词 preposition 连词 conjunction 动词 verb 主动词main verb 及物动词transitive verb 不及物动词intransitive verb 系动词link verb 助动词auxiliary verb 情态动词 modal verb 规则动词regular verb 不规则动词irregular verb 短语动词phrasal verb 限定动词finite verb 非限定动词infinit e verb 使役动词causative verb 感官动词 verb of senses 动态动词 event verb 静态动词st ate verb 感叹词exclamation 形容词adjective
英语语法大全 1 (see 、hear 、notice 、find 、feel 、listen to 、look at (感官动词)+do eg:I like watching monkeys jump 2 （比较级and 比较级）表示越来越怎么样 3 a piece of cake =easy 小菜一碟（容易） 4 agree with sb 赞成某人 5 all kinds of 各种各样a kind of 一样 6 all over the world = the whole world 整个世界 7 along with同……一道，伴随…… eg : I will go along with you我将和你一起去the students planted trees along with their teachers 学生同老师们一起种树 8 As soon as 一怎么样就怎么样9 as you can see 你是知道的 10 ask for ……求助向…要…（直接接想要的东西）eg : ask you for my book 11 ask sb for sth 向某人什么 12 ask sb to do sth 询问某人某事ask sb not to do 叫某人不要做某事 13 at the age of 在……岁时eg：I am sixteen I am at the age of sixteen 14 at the beginning of …………的起初；……的开始 15 at the end of +地点/+时间最后；尽头；末尾eg : At the end of the day 16 at this time of year 在每年的这个时候 17 be /feel confident of sth /that clause +从句感觉/对什么有信心，自信 eg : I am / feel confident of my spoken English I feel that I can pass the test 18 be + doing 表：1 现在进行时2 将来时 19 be able to (+ v 原) = can (+ v 原）能够…… eg : She is able to sing She can sing 20 be able to do sth 能够干什么eg :she is able to sing 21 be afraid to do (of sth 恐惧，害怕…… eg : I'm afraed to go out at night I'm afraid of dog 22 be allowed to do 被允许做什么 eg: I'm allowed to watch TV 我被允许看电视I should be allowed to watch TV 我 应该被允许看电视 23 be angry with sb 生某人的气eg : Don't be angry with me 24 be angry with(at) sb for doing sth 为什么而生某人的气 25 be as…原级…as 和什么一样eg : She is as tall as me 她和我一样高 26 be ashamed to 27 be away from 远离 28 be away from 从……离开 29 be bad for 对什么有害eg : Reading books in the sun is bad for your eyes 在太阳下看书对你的眼睛不好 30 be born 出生于 31 be busy doing sth 忙于做什么事be busy with sth 忙于…… 32 be careful 当心；小心33 be different from……和什么不一样 34 be famous for 以……著名35 be friendly to sb 对某人友好 36 be from = come from 来自eg ：He is from Bejing He comes from Bejing Is he from Bejing ? Does he come from Bejing ? 37 be full of 装满……的be filled with 充满eg: the glass is full of water the glass is filled with water
热门流行英语短语英语单词英语俚语英语句子大全Beat generation 垮掉的一代 Tea-ceremony 茶道 Badger game 美人计 Scene stealer 抢镜头的人 Hooligan 阿飞，足球流氓 Repeated offender 惯犯 Double agent 双重间谍 Mr. Big 黑社会老大 Love child 私生子 Box news 花边新闻 Screen agers 整天看电视玩电脑的孩子 June-December wedding 双方年龄悬殊的婚姻 King’s English 标准英语 Leap day/year 闰日2.29/年366 Maid of Orleans 圣女贞德 Narrow squeak(口)九死一生的脱险 Ninjaturtle 忍者神龟 Poet laureate 桂冠诗人 Ponytail 马尾辫 Protestant 新教徒
Pulitzer Prize 普利策奖 Rat race 激烈的竞争 Red-light district 红灯区 Reader’s Digest 读者文摘 Russian roulette 俄罗斯轮盘赌 Sexual harassment 性骚扰 Short fuse 易怒的脾气 Soft-soap 奉承讨好 Silent contribution 隐名捐款 Silly money 来路不明的钱 Silver screen 银幕，电影界 Summer complaint 夏季病，拉肚子Tenth-rate 最低等的，劣等的 Vertical/lateral thinking 纵向，横向思维Wide-body 大部头的作品 Wheel of life (佛教)轮回 Xenomania 媚外 Yearbook 年鉴年刊 Zen 禅 Paparazzi 狗仔队 Show people 娱乐界人士 Exotic dance 脱衣舞
正确的电脑开关机顺序 由于电脑在刚加电和断电的瞬间会有较大的电冲击，会给主机发送干扰信号导致主机无法启动或出现异常，因此，在开机时应该先给外部设备加电，然后才给主机加电。但是如果个别计算机，先开外部设备（特别是打印机）则主机无法正常工作，这种情况下应该采用相反的开机顺序。关机时则相反，应该先关主机，然后关闭外部设备的电源。这样可以避免主机中的部位受到大的电冲击。在使用计算机的过程中还应该注意下面几点：而且 WINDOWS 系统也不能任意开关，一定要正常关机；如果死机，应先设法“软启动”，再“硬启动”（按 RESET 键），实在不行再“硬关机”（按电源开关 数秒种）。 在电脑运行过程中，机器的各种设备不要随便移动，不要插拔各种接口卡，也不要装卸外部设备和主机之间的信号电缆。如果需要作上述改动的话，则必须在关机且断开电源线的情况下进行。 不要频繁地开关机器。关机后立即加电会使电源装置产生突发的大冲击电流，造成电源装置中的器件被损坏，也可以造成硬盘驱动突然加速，使盘片被磁头划伤。因此，这里我们建议如果要重新启动机器，则应该在关闭机器后等待 10 秒钟以上。在一般情况下用户
不要擅自打开机器，如果机器出现异常情况，应该及时与专业维修部门联系。 鼠标的操作 Windows 中的许多操作都可以通过鼠标的操作完成。 二键鼠标有左、右两键，左按键又叫做主按键，大多数的鼠标操作是通过主按键的单击或双击完成的。右按键又叫做辅按键，主要用于一些专用的快捷操作。 鼠标的基本操作包括指向、单击、双击、拖动和右击。 （1）指向：指移动鼠标，将鼠标指针移到操作对象上。 （2）单击：指快速按下并释放鼠标左键。单击一般用于选定一个操作对象。 （3）双击：指连续两次快速按下并释放鼠标左键。双击一般用于打开窗口，启动应用程序。 （4）拖动：指按下鼠标左键，移动鼠标到指定位置，再释放按键的操作。拖动一般用于选择多个操作对象，复制或移动对象等。（5）右击：指快速按下并释放鼠标右键。右击一般用于打开一个与操作相关的快捷菜单。
小学英语语法大全 第一章名词 一、定义 名词是表示人或事物名称的词。它既可以表示具体的东西，也可以是表示抽象的东西。 二、分类 1. 名词可以根据意义分为普通名词和专有名词 如：john is a student student是普通名词，john是专有名词 普通名词前可以用不定冠词a/an, 定冠词the 或不加冠词，专有名词前一般不加冠词，专有名词的首字母要大写。 2. 普通名词又可以分为个体名词、集体名词、物质名词和抽象名词，其中个体名词与集体名词是可数名词，物质名词和抽象名称是不可数名词。 3. 专有名词 专有名词是表示人名、地名、团体、机构、组织等的专有名词，多为独一无二的事物。 三、名词的数 1、名词分为可数名词和不可数名词。 可数名词——可以数的名词 不可数名词——数不清（没有复数） drink?milk tea water orange juice coke coffee porridge food?rice bread meat fish fruit cake dumplings 2、可数名词与不定冠词a(an)连用有数数形式，不可数名词不能与不定冠词a(an)连用，没有复数形式 many+可数名词复数 much/a little+不可数名词 some, any , a lot of (lots of) 两者都可以修饰。 3、可数名词可以直接用数词来修饰 不可数名词数词 +量词 +of + 名词 对可数名词的数量提问用how many 对不可数名词的数量提问用 how much 4、不可数名词的量有以下两种表示方法： 1） some, much ,a little ,a lot of ,a bit of , plenty of 用等表示多少。 注意既可以与可数名词复数，又可以与不可数名词连用的有：plenty of ,some ,a lot of ,lots of ,most of 等。 如there is much water in the bottle .瓶中有很多水。
句子种类 一、单项选择（共20小题；共20分） 1. , and you'll pass the English exam. A. Study hard B. Studied hard C. To study hard D. Studying hard 2. terrible weather we've been having these days! A. How a B. What a C. How D. What 3. Boys and girls, up your hands if you want to take part in the summer camp(夏令营). A. putting B. to put C. put D. be put 4. --- We will build a subway in Fuzhou before 2014. --- Wow, ! Will it pass our place? A. what an excited news B. how excited the news is C. what exciting news D. how exciting news 5. --- I hear there will be a concert of Li Yuchun and I've been waiting for it. will it start? --- Well, take it easy. In two days. A. How soon B. How long C. How often D. How far 6. --- Hi, Sam. Your mother's busy these days, ? --- Yes. But she says she'll be free soon. A. has she B. is she C. hasn't she D. isn't she 7. I don't think he will agree with me, ? A. won't he B. will he C. does he D. isn't he 8. --- He has to stay at home, ? --- Yes, his mother is ill. A. doesn't he B. hasn't he C. don't they D. does he 9. You'd better come tomorrow, ? A. won't you B. would you C. didn't you D. hadn't you 10. --- She learns English by herself. --- clever girl she is! A. How B. How a C. What a D. What 11. --- Let's go and play basketball, ? --- That's wonderful. A. will you B. do you C. won't we D. shall we 12. lucky people they are!