Preparation of chitosan–nylon-6blended membranes containing silver ions as antibacterial materials
Yunli Ma,Tao Zhou and Changsheng Zhao *
College of Polymer Science and Engineering,State Key Laboratory of Polymer Materials Engineering,
Sichuan University,Chengdu 610065,PR China
Received 23July 2007;received in revised form 31October 2007;accepted 5November 2007
Available online 13November 2007
Abstract—Chitosan–nylon-6blended membranes were prepared by combining solvent evaporation and a phase inversion technique,and then used to chelate silver ions.Gram-positive bacteria (Staphylococcus aureus )and Gram-negative bacteria (Escherichia coli )were used to study the antibacterial properties of the membranes.Fourier-transform infrared spectroscopy (FTIR)and di?erential scanning calorimetry (DSC)indicated hydrogen-bond interactions between chitosan and nylon-6.From the scanning electron microscopy (SEM)pictures,it was observed that with the increase of nylon-6content,the blended membrane gradually became a material with porous morphology.After chelating silver ions,the tensile strength of the membranes increased.The antibacterial activity with the variation of chitosan content,the pH value and the concentration of the silver nitrate solution used to prepare Ag +-loaded membranes were investigated systematically.The results indicated that the chitosan–nylon-6blended membranes with Ag +were antibacterial to both Gram-positive bacteria and Gram-negative bacteria.The antibacterial activity improved with the increased chitosan content due to the larger amount of silver ions loaded.The antibacterial property of the chitosan–nylon-6blended membranes could be primarily attributed to the content of chitosan and silver ions as well as the surface morphology of the membranes.
ó2007Elsevier Ltd.All rights reserved.
Keywords:Chitosan;Nylon-6;Silver ions;Antibacterial property
1.Introduction
Chitosan is a natural nontoxic biopolymer derived by the deacetylation of chitin.Owing to its biocompatibil-ity,biodegradability,antibacterial and antifungal activ-ities,chitosan has become,in the past 20years,a much sought-after material for a variety of applications including biomedical devices,in wound healing,con-trolled drug delivery,1food packing,2heavy metal chelating agents 3,4and waste removal.5,6To extend the applications of chitosan,several approaches have been used for the modi?cation of chitosan,such as graft poly-merization 7and blending with other natural or synthetic polymers.8,9In particular,modi?cation of chitosan by
means of blending with other polymers is a convenient and e?ective method for practical utilization.10–13How-ever,little attention focuses on the e?ects of blending on the antibacterial properties of chitosan.14
The antibacterial activity of chitosan,arising from its polycationic nature,is well known for a variety of bacteria and fungi.15The interaction between the posi-tively charged chitosan and the negatively charged microbial cell wall leads to the leakage of the intracell-ular constituents.The binding of chitosan with DNA and the inhibition of mRNA synthesis occurs via the penetration of chitosan into the nuclei of the micro-organisms and interfering with the synthesis of mRNA and proteins.
However,the antibacterial activity of chitosan is var-iable and is a?ected by many factors such as molecular weight,pH value,and water solubility.16,17Also,chito-san shows antibacterial activity only in an acid medium,
0008-6215/$-see front matter ó2007Elsevier Ltd.All rights reserved.doi:10.1016/j.carres.2007.11.006
*Corresponding author.Tel.:+862885400453;fax:+862885405402;e-mail addresses:zhaochsh70@https://www.doczj.com/doc/0a8976996.html, ;zhaochsh70@
https://www.doczj.com/doc/0a8976996.html,
Available online at https://www.doczj.com/doc/0a8976996.html,
Carbohydrate Research 343(2008)230–237
which is usually ascribed to the antibacterial mechanism and the poor solubility of chitosan at high pH value.18,19 In addition,chitosan solution shows more e?ective anti-bacterial activity than chitosan membranes,which restricts its convenient usage in the?eld of packing and biomedical devices.
It is well known that chitosan has excellent metal-binding capacities,such as chelating silver ions.20,21 Silver ions have powerful antibacterial activity and are widely used as some antibacterial agents and bio-medical materials.15It is accepted that the amine groups in the chitosan molecules are mainly responsi-ble for the uptake of metal cations by a chelation mechanism,7,22though hydroxyl groups(especially in the C-3position)may also contribute to the sorption. In general,positive ions are bound to chitosan at high pH value,since the amine groups are unprotonated and the electron pair on the amine nitrogen is available for donation to silver ions.At low pH value,the anions are not bound to chitosan,since the amine group is protonated.5
Nylon is widely used in food packing due to its good gas-tightness,good stability and good wear resistance.23 As we know,in the food industry,food quality and safety are major concerns since consumers prefer fresher and minimally processed products.To maintain food quality,the packing?lm carrying food additives such as antioxidants,antimicrobial,colorants,?avors,forti-?ed nutrients and spices is one of the most e?ective methods available.24
The aim of this study is to extend the application of chitosan by blending it with nylon-6and then endow the matrix with antibacterial properties by chelating with silver ions,which may then be used in food pack-ing.Thus,in the present study,chitosan is blended with nylon-6to prepare membranes by combining solvent evaporation and a phase inversion technique,and then silver ions are chelated to the membranes.The antibac-terial properties of the membranes are then systemati-cally investigated.
2.Experimental
2.1.Materials
Chitosan(M w,10,000;deacetylation degree of90%)was purchased from Boao Technology Co.Ltd(Shanghai, China).Nylon-6was donated by the State Key Labora-tory of Polymer Materials Engineering(Sichuan Univer-sity).All the other reagents were obtained from the Chemical Reagent Factory of Kelong,China,which were of analytical grade,and used without further puri-?cation.The evaluation with microorganisms was car-ried out in the Institute of Life Science of Sichuan University.2.2.Preparation of membranes
Required amounts of chitosan and nylon-6were dis-solved in aq formic acid(90%HCO2H).Then,the solu-tion was spread on a glass plate for the solvent evaporation at room temperature for about72h.After peeling o?the plates,the membranes were immersed into sodium hydroxide solution(2M)to neutralize the residual acid.After washing thoroughly using copious amounts of distilled water,the membranes were dried at room temperature.
Chitosan–nylon-6blended membranes containing Ag+were prepared by immersing the chitosan–nylon-6 blended membranes into AgNO3solutions of di?erent concentrations(from0.2mmol/L to1.4mmol/L)and pH values(from pH4to8),with stirring for4h, followed by washing thoroughly with copious amounts of distilled water.Finally,the membranes were dried at room temperature.
The samples were designated as CN10,CN30and CN70,which indicated that the nylon-6content was 10%,30%and70%,respectively,in the blended mem-branes before chelating with silver ions.The thickness of the membranes was about250l m,which was deter-mined by a thickness tester.
2.3.Characterization of the membranes
To investigate the interaction between chitosan and nylon-6,an FTIR spectrum of the blended membrane was obtained using a Fourier-transform instrument (Nicolet-560,Nicolet https://www.doczj.com/doc/0a8976996.html,A).For scanning electron microscopy(SEM)observation,the samples were dried at room temperature,and then attached to the sample supports and coated with a gold layer.The SEM images were recorded using an S-2500C microscope(Hitachi, Japan).Sensitive di?erential scanning calorimetry (DSC,EXSTAR6000)was used to study the thermal stability of the chitosan–nylon-6blended membranes. The samples were sealed into aluminum pans,and an empty pan was used as a reference.The temperature was raised from40°C to300°C at a heating rate of 10°C/min.
Tensile testing was performed on each type of mem-brane as previously reported.25Brie?y,the tensile strength of the membranes(dumbbell-shaped specimens, width4mm)were determined at room temperature with a universal tensile testing machine(AG-10TA)operated at a cross-head speed of50mm/min,pre-load of1kg, and grip-to-grip gap of30mm.For each type of mem-brane,?ve specimens were used.
2.4.Antibacterial activity tests
The antibacterial activity of the membranes was tested by an inhibition zone method.26In the method,two
Y.Ma et al./Carbohydrate Research343(2008)230–237231
kinds of di?erent bacteria including Gram-positive bac-teria(Staphylococcus aureus)and Gram-negative bacte-ria(Escherichia coli)were used.
For measurement of the antibacterial activity,all membranes were kept in distilled water for1h.Then, the membrane samples were punched to make disks (diameter=8mm),and the antibacterial activity was determined by a modi?ed agar di?usion assay(disk test).The plates were examined for possible clear zones after incubation at37°C for24h.The presence of any clear zone that formed around the?lm disk on the plate medium was recorded as an indication of inhibition against the microbial species.Suspension cultures with-out any membranes were used as a control.The e?ect of the chitosan content in the blended membranes,the pH value and the concentration of the silver nitrate solution used for preparing the silver-ions-loaded membranes was investigated.
3.Results and discussion
3.1.Fourier transform infrared spectroscopy(FTIR) spectra
The FTIR spectra of the chitosan–nylon-6blended membranes without silver ions are shown in Figure1 to illustrate the interaction between the chitosan and nylon-6.Firstly,attention must be paid to the displace-ment of the amide I band of pure nylon-6,located at 1641.40cmà1toward smaller wavenumbers(lower energy)with an increase in chitosan content.Mean-while,in the curve of CN30,a new peak appeared at about1585.49cmà1,which may be attributed to the e?ect of hydrogen bonds formed between chitosan and nylon-6.According to the former literature,26the inter-hydrogen bonds formed between two di?erent macromolecules are stronger than those formed between the molecules of the same polymer.Thereby,the inter-hydrogen bonds between chitosan and nylon were prone to formation.
To study the chelation between chitosan and silver ions,the spectra of the membranes containing silver ions were studied,as shown in Figure2.It was revealed that with the addition of silver ions,the peak for the amide I band of chitosan shifted toward smaller wavenumbers. For pure chitosan and chitosan–Ag+,the displacement number was about33cmà1(from1623.03cmà1to 1590.38cmà1),which indicated the strong interaction between chitosan and silver ions.Maybe the‘inductive e?ect’caused by the coordination interaction between NH2groups of the chitosan and silver ions led to the shift of the above peaks.Similarly,for the CN30mem-branes,the shift in wavenumbers(from1585.49cmà1to 1581.84cmà1)was also observed after chelating silver ions,but the shifted number was smaller than that for the pure chitosan.From the above data,it is suggested that the coordination interaction between chitosan and silver ions becomes stronger with an increase in chitosan content.
3.2.Surface morphology of the membranes
Figure3shows the scanning electron micrographs (SEM)of the prepared membranes.The pure chitosan membrane displayed a?at dense surface(Fig.3a).With an increase in the amount of nylon-6in the
blended
membranes,the smooth surface gradually disappeared.The ?at dense surface of the chitosan membrane became progressively undulating.This result is in accord with the previous report.26For the blended membrane CN30,a scattered round plaque-like structure was observed as shown in Figure 3c,which was possibly due to the immiscibility of the two polymers.27When the chitosan ratio increased to 70%,as the membrane CN70,a porous structure was observed,as shown in Figure 3d.For the pure nylon-6membrane,it showed a particular morphology (Fig.3e),which might be called a ‘snow?ake’structure.These were caused by the phase inversion when the membranes were immersed in sodium hydroxide after the solvent evaporation,since the solvent was not vaporized completely for 72h.When
silver ions were incorporated into the membranes,lipid droplet-like dents were observed on the membrane surfaces.Generally,the membrane structure could be modulated by the variation of the chitosan ratios in the blended polymers.
3.3.Thermal analysis of the membranes
To study the thermal properties of the chitosan–nylon-6blended membranes,the di?erential scanning calori-metry (DSC)curve (?rst scan)of the prepared mem-branes is shown in Figure 4.Glass transition temperatures (T g )were not observed both for the pure chitosan and nylon-6.A broad endotherm was observed around 60°C for the chitosan–Ag +membrane,which
is
Figure 3.The scanning electron micrographs of the top surface of the prepared membranes.(a)Pure chitosan;(b)CN10;(c)CN30;(d)CN70;(e)pure nylon-6;(b 0)CN10–Ag +;and (c 0)CN30–Ag +.
Y.Ma et al./Carbohydrate Research 343(2008)230–237233
an endothermic peak that exists for most polysaccha-rides at low moisture contents.28In the nylon-6curve,a melting endothermic peak was observed at 225°C,which was associated with the crystalline polymer frac-tion.The characteristic peak of chitosan at about 60°C became smaller with increasing nylon-6content,and the melting peak of nylon at 225°C became smaller with decreasing the nylon-6content,but no obvious change in the melting temperature was observed.This indicated that the nylon crystallization decreased after blending with chitosan,and there was interaction be-tween chitosan and nylon-6.From the FTIR and DSC analysis,it is suggested that inter-hydrogen bonds exist between chitosan and nylon.3.4.Tensile strength of the membranes
Figure 5shows the tensile strength of the prepared mem-branes.As shown in the ?gure,it is clearly observed that
all the membranes containing silver ions displayed an increased tensile strength over that of the corresponding membranes without silver ions,which may be attributed to the strong interaction between chitosan and silver ions.As illustrated in the FTIR analysis (Fig.2),the coordination bonds formed between NH 2groups of chitosan and silver ions made the inter-molecule inter-action more intense,and thus improved the tensile strength.
When the nylon content is lower than 30%in the blended membranes,the di?erence of the tensile strength is not distinct;however,the CN10–Ag +membrane showed increased tensile strength,with the values of 42.08MPa.Besides the coordination interaction between chitosan and silver ions,there were inter-hydro-gen bonds between chitosan and nylon,which made the molecules tight binding,so the tensile strength increased.With more nylon-6incorporated,the strength decreased,which could be due to the formation of the porous struc-ture induced by the preparation process,as shown in SEM photos (Fig.3d and e).Similarly,the tensile strength obtained for pure nylon-6was lower than the theoretical value (40–60MPa),which could also be attributed to the snow-like structure formed in the prep-aration process.As a result,the proper hydrogen bond formed between chitosan and nylon can improve the mechanical strength of the blended membranes,and the dense and uniform structures are bene?cial in main-taining higher mechanical strengths.3.5.Antibacterial activity of the membranes
3.5.1.E?ect of the chitosan content.Figure 6shows the photographs of the antibacterial test.It is clearly observed that the membranes loaded with silver ions showed antibacterial activity against both S.aureus and E.coli .The e?ect of chitosan content in the Ag +-loaded membranes on the antibacterial activity against S.aureus and E.coli as determined by the disk method is shown in Figure 7.As shown in the ?gure,the inhibi-tion zone diameter became larger with more chitosan incorporated,and when the chitosan content was more than 70%,the di?erences of the antibacterial activity were not obvious.However,the nylon-6membrane did not exhibit antibacterial activity,even after immers-ing in silver nitrate solution,since there was no interac-tion between nylon-6and Ag +.In the test,pure chitosan membrane without silver ions showed small inhibition zone,which could be due to the decreased amount of the positive charge of chitosan after being partly neu-tralized with sodium hydroxide;thus the interaction with the negative cell wall of the bacteria became weaker.It is well known that chitosan has antibacterial activity,and the antibacterial activity of chitosan membrane is usually lower than that for chitosan solution.After incorporating silver ions,the antibacterial activity
of
Figure 5.Tensile strength of the blended membranes.Data are expressed as the means ±SD,n =5.
234Y.Ma et al./Carbohydrate Research 343(2008)230–237
chitosan greatly increased,and the inhibition zone diameter increased to about two times larger (data not shown).As we know,silver ions have e?ective antibacte-rial activity.The increased antibacterial activity of the Ag +-incorporated membranes was caused by the Ag +.It is reported that Ag +adheres to the negative charged
cell wall,changing the cell wall permeability.This action,coupled with protein denaturation,induces cell lysis and death.29The antibacterial activity of Ag +is also related to its ability to modify the DNA replication mechanisms as well as to cause abnormalities in the size,cytoplasmic contents,cell membranes,and outer cell layers of sensitive cells.30–32
For further understanding of the e?ect of silver ions on antibacterial activity,the amount of Ag +in the blended membranes was investigated as shown in Figure 8.It was clearly observed that with the increase of nylon-6content in the membranes,the amount of loaded silver ions https://www.doczj.com/doc/0a8976996.html,bined with Figure 7,it was easy to conclude that the silver ions had a great e?ect on the antibacterial activity,which further proved the point of the above discussion.In addition,the mor-phology of the chitosan–nylon-6blended membranes also a?ected the antibacterial activity.With an increase in the nylon-6content of the membranes,the ?at dense surface of the chitosan membrane became progressively undulating,which might be conducive to bacterial adhe-sion and colonization.This was in accord with the ?nd-ings of the previous research:the rougher surfaces may be more conducive to cellular and bacterial coloniz-ation.14,33,34In a word,after incorporating silver ions,the antibacterial activity of the chitosan–nylon-6blended membrane was improved greatly.In addition,the antibacterial activity is a?ected by the content
of
Figure 6.Photographs of the antibacterial test results of the blended membranes with di?erent chitosan content against E.coli (a,c)and S.aureus (b,d).(a)Chitosan–Ag +membrane against E.coli ;(b)chitosan–Ag +membrane against S.aureus ;(c)CN30–Ag +membrane against E.coli ;(d)CN30–Ag +membrane against S.aureus ;and (e)agar plate incorporated bacteria without any membrane as
control.
chitosan and the morphology of the chitosan–nylon-6 blended membranes.
3.5.2.E?ect of the pH value of the silver nitrate solution.Since silver ions had a great e?ect on the anti-bacterial activity,we examined the e?ect of the silver nitrate solution used to treat the CN30membrane on the antibacterial property.Figure9shows the antibacte-rial activity of the CN30–Ag+membrane as a function of the pH value of the silver nitrate solution.As shown in the?gure,the membrane exhibited the best antibacte-rial activity at pH6.Chitosan is a weak polybase with a p K a of6.5,28which may be more suitable for the unprot-onated amine nitrogen to donate the electron pair to sil-ver ions.Thus,larger amounts of the silver ions were incorporated to the membrane,and the antibacterial activity improved.
3.5.3.E?ect of the concentration of the silver nitrate solution.Figure10shows the e?ect of the concentra-tion of the silver nitrate solution used to prepare the Ag+-loaded membranes on the antibacterial activity. As shown in the?gure,when the concentration of the silver nitrate solution increased from0.2to0.5mmol/ L,the antibacterial activity increased.However,there seemed no signi?cant di?erence when the concentration increased over0.5mmol/L.
As shown in Figure8,when the concentration of the silver nitrate solution was0.5mmol/L,the Ag+-bound capacity in the pure chitosan membrane was48.2mg per gram of chitosan,which is in agreement with the previous report.24But for the CN30membrane,the Ag+-bound capacity is lower than that of the pure chito-san membrane,with a value of26.6mg per gram of chitosan.This is probably attributed to the hydrogen bonds formed between NH2groups of chitosan and nylon,which served to decrease the number of NH2 groups in chitosan used for coordination with silver ions.The data indicate that the Ag+-incorporated in the CN30membrane may have reached saturation, and no obvious di?erence of the antibacterial activity was observed when the concentration of the silver nitrate solution was increased to over0.5
mmol/L.
In conclusion,the content of chitosan and silver ions incorporated in the blended membranes has a great e?ect on the antibacterial activity.Thus,the pH value and the concentration of the silver nitrate solution,which can a?ect the chelated content of silver ions in the blended membranes,a?ects the antibacterial activity.
4.Conclusions
In summary,all the chitosan–nylon-6blended mem-branes containing silver ions were antibacterial to both Gram-negative bacteria(E.coil)and Gram-positive bac-teria(S.aureus),and there was no signi?cant di?erence between the two types.With increased nylon-6content, the antibacterial property of the blended membranes decreased,which may be attributed to the decreased chitosan and Ag+content in the blended membranes. Besides,the surface morphology of the blended mem-branes may also a?ect the antibacterial activity of the blended membranes.From the mechanical analysis,it is clear that the tensile strength of the membranes in-creased after incorporating Ag+.In this study,a simple way was proposed to extend the application of chitosan by blending with nylon-6and endow the material with antibacterial properties that render it useful for food packing.Of course,by blending chitosan with other syn-thetic polymers,new food packing materials with anti-bacterial activity may be obtained.
Acknowledgments
This work was?nancially sponsored by the National Natural Science Foundation of China(Nos.50403028, 50673064).
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图表与口诀记忆when、as、while的区别 1.图表与口诀前知识 关键是比较主从句子的动词，看其动词的持续性。瞬间的理解成点，持续的理解成线。主从关系有：点（点点、点线），线线，线点。 点：为瞬间动词，准确地称为“终止性动词”，指动词具有某种内在界限的含义，一旦达到这个界限，该动作就完成了。如come（来），一旦“到来”，该动作就不再继续下去了。 瞬间动词：arrive, begin, borrow, become, buy, catch, come, die, find, go，give, graduate, join, kill, lose, leave, marry, realize… 线：为非瞬间动词，准确地称为叫“延续性动词”。包括动态动词静态动词。 动态动词：live, sit, stand, study, talk, work, write… 静态动词（状态动词）：情感、看法、愿望等。Be, belong, consist, exist, feel, hate, have, hope, love, want… 兼有瞬时和非瞬时的动词：feel，look，move，run，work，write…，需要根据不同的语境判断。 2. when、as、while的区别一览表 【表格说明】：第一个点或者线表示从句谓语动词的持续性特征，黑点表示从句所表示的动作持续短，为瞬间动词，线表示持续长，为非瞬间动词。1~7为主句与从句所表示的动作时间有重合，第8为主句与从句所表示的动作不是同时发生，而是有先后顺序。 线线重相并发生， 长线” 【主句谓语为非瞬间动词中的 动态动词】 【记忆：等线动， 相并发生，但： 【主句谓语为非瞬间动词中的 静态动词】 【记忆：等线动，
一、根据从句动作的持续性来区分 1.“主短从长”型：即主句是一个短暂性的动作，而从句是一个持续性动作，此时三者都可用。如： Jim hurt his arm while [when, as] he was playing tennis. 吉姆打网球时把手臂扭了。 As [When, While] she was waiting for the train, she became very impatient. 她在等火车时，变得很不耐烦。 注意：as用于引出一个持续性动词表示“在……期间”时，其谓语通常只能是那些含有动作和发展意味的动词，一般不能是那些不用于进行时态的动词(如be, seem, love, want, agree, see, know, have 等)，所以下面一句中的while不能换为as： A：I’m going to the post office. 我要去邮局。 B：While you are there, can you get me some stamps? 当你在邮局时，能帮我买几张邮票吗? 若主句与从句表示的是两个几乎同时发生的动作，含有类似汉语“刚要……就”“正要……却”的意思，英语一般要用as(也可用when)，且此时通常连用副词just。且此时，从句一般用进行时，主句用短暂性动词的一般时态。【注意与六区别】 I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住了。 Just as [when] the two men were leaving, a message arrived. 就在这两个人要离开的时候，突然有了消息。 2.“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态，且强调主句动作或状态延续到从句所指的整个时间，此时通常要用while。如： I always listen to the radio while I’m driving. 我总是一边开车一边听收音机。 He didn’t ask me in; he kept me standing at the door while he read the me ssage. 他没有让我进去，他只顾看那张条子，让我站在门口等着。 但是，若主句和从句所表示的两个同时进行的动作含有“一边……一边”之意时，则习惯上要用as。如： He swung his arms as he walked. 他走路时摆动着手臂。 I couldn’t remember a story to tell the children, so I made one up as I went along. 我想不出有什么故事可给孩子讲了，只好现编现讲。 3.“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用a s或when，但不能用while。如：
RF-BM-S01低功耗蓝牙 透传模块（BQB认证）数据手册（V1.50） 深圳市信驰达科技有限公司 2013-3-14
1.模块概述 为方便蓝牙4.0(BLE)应用技术在各个行业产品中的移植和使用，信驰达科技特别研发了BM-S01低功耗蓝牙透传模块，并通过了蓝牙技术联盟认证（BQB），详见：RF- RF-BM-S01 https://https://www.doczj.com/doc/0a8976996.html,/tpg/EPL_Detail.cfm?ProductID=27655。客户的现有产品或者方案配合此透传模块，能方便地和iPhone5等移动设备(需支持蓝牙4.0)相互通讯。实现一些智能化控制和管理。 RF-BM-S01是一款采用美国德州仪器TI蓝牙4.0CC2540作为核心处理器的高性能、超低功耗（Bluetooth Low Energy）射频收发系统模块，它拥有目前行业内较小封装的尺寸（13.7x17.1x2.5mm）。该模块预装RF-star’s RF-BLE固件并符合BLE协议标准。 客户MCU通过串口与模块相连。模块启动后会自动广播，已打开特定APP的移动设备会对其进行扫描和对接，成功之后便可以通过通用串口和移动设备进行双向通信，用户可以通过数据通道和指令通道，进行数据交换或者对通讯参数的控制，数据具体含义由上层应用程序自行定义。移动设备可以通过APP对模块进行写操作，写入的数据将通过串口发送给客户的MCU。模块收到来自客户MCU串口的数据包后，将自动转发给移动设备。 2.接线示意图 *注：在老版本的资料中BRTS,BCTS被称为CCS,MCS 3.性能特点 1.使用方便快捷，无需任何蓝牙协议栈应用经验。 2.用户接口使用通用串口设计，双向读取，操作简单。 3.支持串口AT指令调整转发速率（动态功耗调整），模块命名。 4.串口数据包长度，可以是200byte以下(含200)的任意长度。 5.支持高速模式，最快可达4K/S，可稳定工作在2.5K-2.8K。
as when while 的区别和用法 as when while的用法 一、as的意思是“正当……时候”,它既可表示一个具体的时间点，也可以表示一段时间。as可表示主句和从句的动作同时发生或同时持续，即“点点重合”“线线重合”；又可表示一个动作发生在另一个动作的持续过程中，即“点线重合”， 但不能表示两个动作一前一后发生。如果主句和从句的谓语动词都表示持续性的动作，二者均可用进行时，也可以一个用进行时，一个用一般时或者都用一般时。 1、As I got on the bus，he got off. 我上车，他下车。（点点重合）两个动作都是非延续性的 2、He was writing as I was reading. 我看书时，他在写字。（线线重合）两个动作都是延续性的 3、The students were talking as the teacher came in. 老师进来时，学生们正在讲话。（点线重合）前一个动作是延续性的，而后一个动作时非延续性的 二、while的意思是“在……同时（at the same time that )”“在……期间(for as long as, during the time that）”。从while的本身词义来看，它只能表示一段时间，不能表示具体的时间点。在时间上可以是“线线重合”或“点线重合”，但不能表示“点点重合”。例如： 1、He was watching TV while she was cooking. 她做饭时，他在看电视。（线线重合） 2、He was waiting for me while I was working. 我工作的时候，他正等着我。（线线重合） 3、He asked me a question while I was speaking. 我在讲话时，他问了我一个问题。（点线重合）
产品规格书 PRODUCT SPECIFICATION 深圳云里物里科技股份有限公司 Version V4.1发布时间 2018-04-25 MODEL NO/DESCRIPTION 产品名称:蓝牙模块MS50SFA1C 产品型号:MS50SFA1C
版本说明
目录 版本说明 (2) 1.概述 (4) 2.应用领域 (5) 3.电气参数 (5) 4.模块尺寸图 (6) 5.引脚定义 (6) 6.模块配置 (7) 6.1透传模块出厂默认值 (7) 6.2蓝牙服务UUID (7) 6.3UUID描述 (7) 6.4工作模式 (7) 6.5模块应用示意图 (8) 7.透传数据【服务UUID：0xFFF0】(APP端) (8) 8参数设置说明 (8) 9.模块测试 (112) 10.支持的设备 (14) 11.PCB设计说明 (145) 12.注意事项 (15) 13.包装信息 (155) 14.质量保证 (166)
1.概述 MS50SFA1C串口模块采用nRF52810芯片,通过UART(串口)操作可以实现模块与手机之间数据传输。本模块从模块，具有命令控制可以修改模块的广播名称，修改广播间隔和连接间隔。使用该模块用户可以快速把数据以蓝牙方式进行传输。 正面反面 产品特征 远距离：10-60米（空旷环境） BLE协议栈深度优化，睡眠功耗1uA以下 传输速率最块可达7Kbps 支持串口指令配置 支持Android4.3+,7+ 无需MFi
2.应用领域 该模块主要用于短距离的数据无线传输领域。可以方便的和PC机的蓝牙设备相连，也可以与智能手机之间的数据互通。避免繁琐的线缆连接，能直接替代串口线。 ※健身器材设备，如跑步机，健身器等 ※医疗器械设备，如脉博测量计，心率计等 ※家用休闲设备，如遥控器，玩具等 ※办公用品设备，如打印机，扫描仪等 ※商业设备，如收银机，二维码扫描器等 ※手机外设配件，如手机防丢器等 ※汽车设备，如汽车维修仪等 ※其它人机交互设备 3.电气参数 参数测试值备注 工作电压 1.8-3.6V直流 工作频率2400-2483MHz可编程 频率误差+/-20KHz Null 发射功率-40~+4dBm可调整 接收灵敏度-96dBm Null 接收电流 4.6mA标准模式 发射电流 4.6mA发射功率为0dBm时 睡眠功耗1uA以下Null 遥控距离10-60米BER<0.1%,空旷 天线50ohm Null 模块尺寸16*12*2mm Null 存储大小192KB
When while as区别 一、根据从句动作的持续性来区分 1、“主短从长”型：即主句是一个短暂性动作，而从句是一个持续性动作，此时三者都可用。如： Jim hurt his arm while［when， as］ he was playing tennis. 吉姆打网球时把手臂扭伤了。 2、“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态，且强调主句动作或状态延续到从句所指的整个时间，此时通常要用while。 I always listen to the radio while I’m driving. 我总是一边开车一边听收音机。 He didn’t ask me in; he kept me standing at the door while he read the message. 他没有让我进去，他只顾看那张条子，让我站在门口等着。 但是，若主句和从句所表示的两个同时进行的动作含有“一边……一边”之意时，则习惯上要用as。如： He swung his arms as he walked. 他走路时摆动着手臂。 3、“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用as 或when，但不能用while。如： It was raining hard when [as] we arrived. 我们到达时正下着大雨。 二、根据主句与从句动作是否同时发生来区分 1、若主句与从句表示的是两个同时发生的短暂性动作，含有类似汉语“一……就”的意思，英语一般要用as (也可用when)。如： The ice cracked as [when] I stepped onto it. 我一踩冰就裂了。 2、若主句与从句表示的是两个几乎同时发生的短暂性动作，含有类似汉语“刚要……就”“正要……却”的意思，英语一般要用as(也可用when)，且此时通常连用副词just。如： I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住了。 三、根据是否具有伴随变化来区分 若要表示主句动作伴随从句动作同时发展变化，有类似汉语“随着”的意思，英语习惯上要用as，而不用when或while。如： The room grew colder as the fire burnt down. 随着炉火逐渐减弱，房间越来越冷。 注：若不是引导从句，而是引出一个短语，则用with，不用as。如： With winter coming on, it’s time to buy warm clothes. 随着冬天到来，该买暖和衣裳了。 四、根据从句动作的规律性来区分 若暗示一种规律性，表示“每当……的时候”，英语一般要用when。如： It’s cold when it snows. 下雪时天冷。 五、根据主从句动作的先后顺序来区分 若主句与从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when。
浅谈BLE蓝牙透传模块的应用领域 无线蓝牙透传模块，顾名思义即数据透明传输，透明传输就是在数据传输过程中，发送方和接收方数据的长度和内容完全一致，不需对数据做任何处理，相当于一条数据线或者串口线。一般模块具有半成品的属性，是在芯片的基础上进行加工。换言之，蓝牙模块一般具有二次开发的特性。 云里物里研发的MS48SF2C是一款超低功耗蓝牙模块，通过UART(串口)操作可以实现模块与手机之间数据传输；具有命令控制可以修改模块的广播名称，修改广播间隔和连接间隔。使用该模块用户可以快速把数据以蓝牙方式进行传输；传输距离在10-60米。 应用领域： 一、机器人控制 一个工业机器人系统通常分为机构本体和控制系统两大部分。构成机器人控制系统的要素主要有计算机硬件系统及无线模块操作控制软件、输入/输出设备及装置、驱动器系统、传感器系统。 二、远程抄表 远程抄表系统主要是完成电度计量或信息采集、信息远传、后台软件处理和分析三部分任务。前后两部分技术已经成熟，抄表系统技术关键是解决信息远传——通讯问题。 三、门禁安全管理系统 门禁安全管理系统是新型现代化安全管理系统，它集微机自动识别技术和现代安全管理措施为一体，它涉及电子，机械，光学，计算机技术，通讯技术，生物技术等诸多新技术。它是解决重要部门出入口实现安全防范管理的有效措施。 四、工业数据采集 工业数据采集，是指从传感器和其它待测设备等模拟和数字被测单元中自动采集非电量或者电量信号,送到上位机中进行分析，处理。数据采集系统是结合基于计算机或者其他专用测试平台的测量软硬件产品来实现灵活的、用户自定义的测量系统。 五、无线遥控遥测 无线遥测系统是以计算机为基础的生产过程控制与调度自动化系统。它可以对现场的运行设备进行监视和控制，以实现数据采集、设备控制、测量、参数调节以及各类信号报警等各项功能。
When while as的区别和用法 when的用法 当主句使用持续性动词时. Dave was eating,when the doorbell rang.门铃响时,大卫在吃饭. 2.一个动作紧接着另一个动作发生. When the lights went out, I lit some candles.灯灭了,我赶紧点上一些蜡烛. 3.谈论生命中的某一阶段,或过去的某段时间. His mother called him Robbie when he was a baby. 在他很小时,他妈妈叫他Robbin. 4.指"每一次" When I turn on the TV, smoke comes out the back. 每当我打开电视,就有烟从后面冒出. while/as 的用法 从句多为进行时,而且为持续性动词. I'll look after the children while you are making dinner. 你做饭,我来照顾孩子. 注意事项: (1) “主短从长”型：主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。 Jim hurt his arm while［when，as］he was playing tennis. 吉姆打网球时把手臂扭伤了。 As［When，While］she was waiting for the train，she became very impatient. 她在等火车时，变得很不耐烦。 (2) “主长从长”型：若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。 但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as：
when，while，as引导时间状语从句的区别 when，while，as显然都可以引导时间状语从句，但用法区别非常大。 一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as只能和延续性动词连用。 ①Why do you want a new job when youve got such a good one already？（get 为短暂性动词）你已经找到如此好的工作，为何还想再找新的？ ②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。 ③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。 ④The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。 二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while 和as从句的谓语动作必须是和主句谓语动作同时发生。 1．从句动作在主句动作前发生，只用when。 ①When he had finished his homework，he took a short rest．（finished先发生）当他完成作业后，他休息了一会儿。 ②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。 2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。 ①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。 ②When ／While ／As she was making a phonecall，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。 3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用as。这时，as常表示“随着……”；“一边……，一边……”之意。 ①As the time went on，the weather got worse．（as表示“随着……”之意） ②The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。 ③As years go by，China is getting stronger and richer．随着时间一年一年过去，中国变得越来越富强了。 ④The little girls sang as they went．小姑娘们一边走，一边唱。 ⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。 4．在将来时从句中，常用when，且从句须用一般时代替将来时。 ①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。 ②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。 三、when用于表示“一……就……”的句型中（指过去的事情）。 sb．had hardly（＝scarcely）done sth．when．．．＝Hardly ／Scarcely had sb．done sth．when．．．
蓝牙透传模块选型8大要素 蓝牙作为一种近距离无线通信技术，是无线数据传输最成熟的解决方案，目前蓝牙透传模块已经得到广泛应用，如蓝牙彩灯控制方案、蓝牙医疗设备、蓝牙智能门锁等等。由于蓝牙技术已十分成熟且价格低廉，在物联网新兴领域已得到了充分重视，不过蓝牙透传模块在选型时也应考虑以下几点： 1、传输距离 蓝牙主要分两种功率级别，在蓝牙模块天线可视的情况下，CLASS1标准通信距离100米（当然稳定传输不丢包的传输距离在50米左右），CLASS2标准通信距离10米。实际厂家的蓝牙模块产品中，在天线可视的情况下可以稳定的传更远，如云里物里的蓝牙4.0模块MS49SF1实测稳定通信距离可达90米。 2、接口选择 蓝牙模块的接口分串行接口、数字IO口、模拟IO口、SPI编程口、USB接口及语音接口。一般数据传输时采用串行接口（TTL电平）。 3、传输内容 目前市场上的蓝牙模块数据传送与语音传输是不同型号的模块，采用的芯片不同，用户在选型时应特别注意。云里物里的蓝牙模块都是BLE蓝牙模块，即是数据传送模块，可支用户二次开发。 4、工作方式选择 蓝牙工作时一般分为主机和从机 5、蓝牙模块的控制能力 在工业环境中工作的蓝牙模块，尤其注重稳定性和可监控性，主机系统需要随时知道蓝牙模块的工作状态，好的蓝牙模块应该能够对外提供工作状态指示信号。 6、蓝牙模块传输速度选择 云里物里蓝牙4.0模块MS47SF1实测最高稳定不丢包，蓝牙4.2模块MS49SF2实测最高稳定不丢包传输速度为（下图，左为MS47SF1，右为MS49SF2）
7、供应商选择 选择蓝牙模块或是蓝牙方案，一般选择有研发、生产、销售和售后一体的供应商。很多比较便宜的蓝牙模块厂商，由于受限于资金、技术方面的水平，不能给客户提供完善的技术支持和售后服务。 云里物里专业致力于简化客户的产品应用设计，深耕BLE蓝牙透传模块领域，构建自有研发、测试、生产、销售和售后配套体系，可以很好的服务于终端客户！
蓝牙SPP串口透传模块JDY-31蓝牙模块使用手册
版本 版本日期说明V1.2 2018-09-21 发布版本
一、产品简介与应用 JDY-31蓝牙基于蓝牙3.0 SPP设计，这样可以支持Windows、Linux、android数据透传，工作频段2.4GHZ，调制方式GFSK，最大发射功率8db，最大发射距离30米，支持用户通过AT命令修改设备名、波特率等指令，方便快捷使用灵活。 二、产品应用 JDY-31为经典蓝牙协议、可以与支持蓝牙的电脑（台式、笔记本）、手机（android）通信。可应用于 ◆ Windows电脑蓝牙串口透传 ◆ Android蓝牙串口透传 ◆智能家居控制 ◆汽车ODB检测设备 ◆蓝牙玩具 ◆共享移动电源、共享体重称 ◆医疗仪器 三、模块参数详 型号JDY-31 工作频段 2.4GHZ 通信接口UART 工作电压 1.8-3.6V（建议3.3V） 工作温度-40℃ - 80℃ 天线内置PCB天线 传输距离30米 主从支持从机 模块尺寸19.6 * 14.94 *1.8 mm（长宽高） 蓝牙版本Bluetooth 3.0 SPP STM焊接温度<260℃ 未连接工作电流 4.7mA BLE连接后电流7.3mA 发射功率8db（最大） 接收灵敏度-97dbm SPP最大吞吐量16K bytes/s(android、windows)
JDY-31支持贴片与焊接排针 1、排针应用：排针规格为标准2.54间距排针，只需焊接模块上5个排针孔即可。 2、贴片应用：一般应用只需要连接VCC、GND、RXD、TXD 4个引脚，如需在连接 状态主动断开连接，在连接状态发送AT+DISC
When，While，As引导时间状语从句的区别 when，while，as显然都可以引导时间状语从句，但用法区别非常大。 一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as 只能和延续性动词连用。 ① Why do you want a new job when you’ve got such a good one already？（get为短暂性动词）你已经找到如此好的工作，为何还想再找新的？ ②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。 ③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。 ④ The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。 二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while 和as从句的谓语动作必须是和主句谓语动作同时发生。 1．从句动作在主句动作前发生，只用 when。 ①When he had finished his homework，he took a short rest．（finished 先发生）当他完成作业后，他休息了一会儿。 ②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。 2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。 ①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。 ②When ／While ／As she was making a phone call，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。 3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用 as。这时，as常表示“随着……”；“一边……，一边……”之意。 ① As the time went on，the weather got worse．（as表示“随着……”之意） ② The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。 ③As years go by，China is getting stronger and richer．随着时间一年一年过去，中国变得越来越富强了。 ④The little girls sang as they went．小姑娘们一边走，一边唱。 ⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。 4．在将来时从句中，常用when，且从句须用一般时代替将来时。 ①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。 ②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。 三、when用于表示“一……就……”的句型中（指过去的事情）。
1、什么是蓝牙4.0，蓝牙4.0较之前版本蓝牙的区别。 蓝牙4.0 共3种工作模式，普通蓝牙模式，高速蓝牙模式和低速蓝牙模式，而以前的版本只支持普通蓝牙模式，其他模式不和普通蓝牙模式兼容； 2、蓝牙4.0 是BLE么？ 蓝牙4.0包含BLE, BLE是蓝牙4.0中的单模模式。 3、低功耗蓝牙和普通蓝牙有什么区别？ 最主要的区别是数据包有限制，因此功耗也更低。 4、目前是否所有手机都能支持低功耗蓝牙？ 不是，需要支持蓝牙4.0技术的手机，如苹果、三星、HTC等。 5、低功耗蓝牙4.0是否能够向下兼容之前版本的蓝牙，为什么？ 低功耗蓝牙不向下兼容，低功耗由于需要降低功耗，使用的通讯机制已经和普通蓝牙不同，所以无法通讯。 6、BLE蓝牙速率多少？ 物理层速率1M，实际转发速率是每次连接事件传20字节。 7、低功耗蓝牙模块的传输距离有多远？ 在0dB的情况下，标称100英尺，约60米。 8、BLE模块的传输速率是多大？能传的数据量有多大？ 转发速率最快4K/S,可稳定工作在2.8K/S。能传的数据量有多大，取决于你传多久。 9、BLE模块的抗干扰能力怎么样？穿墙能力如何？ 使用调频通讯方式，37个通讯频点，3个广播频点。可有效避免一些频点干扰。不建议穿墙使用，如果是空心木质墙体可以试试。 10、BLE模块是否为双工模块？ 是的，全双工。 11、BLE模块默认连接间隔是多少？可以调节吗？ V1.X是100ms,V2.0是20ms,V2.0可以调。 12、BEL模块串口数据包的大小可以是多少？ 200字节以内，包含200字节。 13、BLE模块的工作电流怎么计算的？标准的纽扣电池能用多久？ 持续的工作电流对时间积分，再求平均值。一秒一次连接，不计其它功耗，一年以上。 14.产品使用通过的BQB认证模块，还需要过其他蓝牙认证吗？ 只是要过产品的其他认证，比如FCC,CE，蓝牙部分无需再过认证。
When, while, as的区别和用法 版本一 (1) 若主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。 【注】as 用于引出一个持续性动词表示“在……期间”时，其谓语通常只能是那些含有动作(action)和发展(development) 意味的动词，一般不能是那些不用于进行时态的动词(如be, seem, love, want, agree, see, know, have 等)，所以下面一句中的while 不能换为as： A：I’m going to the post office. 我要去邮局。 B：While you’re there, can you get me some stamps? 当你在邮局时，能帮我买几张邮票吗? (2) 若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。 但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as： She sang as she went along. 她边走边唱。 (3) 若从句是一个短暂性动作，主句是一个持续性动作，可用as / when 但不用while： It was raining hard when [as] we arrived. 我们到达时正下着大雨。 (4) 若主从句表示的是两个同时(或几乎同时)发生的短暂性动作，用as / when： I thought of it just when [as] you opened your mouth. 就在你要说的时候，我也想到了。 (5) 若要表示两个正在发展变化的情况，相当于汉语的“随着”，一般用as： Things are getting better and better as time goes on. 随着时间的推移，情况越来越好。 As it grew darker, it became colder. 天色越晚，天气越冷。 (6) 表示“每当…的时候”(暗示一种规律性)，一般要用when： It’s cold when it snows. 下雪时天冷。 He smiles when you praise him. 你夸奖他时他总是笑笑。 (7) 若主从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when： I will go home when he comes back. 他回来时，我就回家去。 (8) when 可用作并列连词，表示“这时(突然)”；while 也可以用作并列连词，表示“而”、“却”(表示对比)；但as 则没有类似用法： We were about to start when it began to rain. 我们正要出发，这时天开始下雨了。 He likes coffee, while she likes tea. 他喜欢咖啡，而她却喜欢茶。 (9) as 和when 后均可直接跟一个名词，构成省略句，但while 一般不这样用： As [When] a boy, he lived in Japan. 他小时候在日本。
When while as 区别 一、根据从句动作的持续性来区分 1、“主短从长”型：即主句是一个短暂性动作，而从句是一个持续性动作，此时三者都可 用。如： Jim hurt his arm while ［ when， as］ he was playing tennis. 吉姆打网球时把手臂扭伤了。 2、“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态， 状态延续到从句所指的整个时间，此时通常要用while 。 且强调主句动作或 I always listen to the radio while I ’ m driving. 我总是一边开车一边听收音机。 He didn ’ t ask me in; he kept me standing at the door while he read the message. 他没有让我进去，他只顾看那张条子，让我站在门口等着。 但是，若主句和从句所表示的两个同时进行的动作含有“一边,, 一边”之意时，则习惯上 要用 as。如： He swung his arms as he walked. 他走路时摆动着手臂。 3、“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用as 或when，但不能用 while 。如： It was raining hard when [as] we arrived.我们到达时正下着大雨。 二、根据主句与从句动作是否同时发生来区分 1、若主句与从句表示的是两个同时发生的短暂性动作，含有类似汉语 “一英语一般要用 as (也可用 when)。如： ,, 就的”意思，The ice cracked as [when] I stepped onto it. 我一踩冰就裂了。 2、若主句与从句表示的是两个几乎同时发生的短暂性动作，含有类似汉语“刚要“正要 ,, 却”的意思，英语一般要用 as(也可用 when)，且此时通常连用副词 ,, just。如： 就” I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住 了。 三、根据是否具有伴随变化来区分 若要表示主句动作伴随从句动作同时发展变化，有类似汉语“随着”的意思，英语习惯上要 用as，而不用 when 或 while 。如： The room grew colder as the fire burnt down.随着炉火逐渐减弱，房间越来越冷。 注：若不是引导从句，而是引出一个短语，则用with ，不用 as。如： With winter coming on, it ’ s time to buy warm clothes. 随着冬天到来，该买暖和衣裳了。 四、根据从句动作的规律性来区分 若暗示一种规律性，表示“每当,, 的时候”，英语一般要用when 。如：It ’s cold when it snows. 下雪时天冷。 五、根据主从句动作的先后顺序来区分 若主句与从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when 。
when/while/as区别用法详解 when, while, as都可作"当……的时候"解，但它们之间也有差别。 若主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用。 He fell asleep when/while/as he was reading. 他看书时睡着了。 when只表示一般的时间关系，它既可指时间的一点，也可指一段时间。用when时，从句的动作可与主句的动作同时发生，也可先于主句的动作，因此when用得最多。如： He was playing basketball when I saw him. 当我看见他的时候，他正在打篮球。 Don't forget to return this book for me, when you go to the library. 你去图书馆时，不要忘记替我还这本书。 while只能指一段时间，而不能指时间的一点。用while时，从句的动作或者与主句的动作同时发生，或者主句的动作是在从句的动作的进展过程中发生的。因此，从句中的谓语必须是表示延续性动作或状态的动词。这是while与when的主要差别。如： When we arrived in Beijing, it was raining. (arrive不是延续性的动词)我们到达北京时，天正在下雨。 Please do not trouble me while I am writing my homework. 我写作业时请不要打扰我。在用when和while连接的从句中，常省略与主句相同的主语和相应的be，而在as连接的从句中一般则不省略。如： He fell asleep while(he was)studying his grammar book.他在阅读语法书的时候睡着了。While in London,he studied music.他在伦敦的时候，研究音乐。 when 可用作并列连词，表示“这时(突然)”；while 也可以用作并列连词，表示“而”、“却”(表示对比)；但as 则没有类似用法： We were about to start when it began to rain. 我们正要出发，这时天开始下雨了。 He likes coffee, while she likes tea. 他喜欢咖啡，而她却喜欢茶。
when, while 和 as 引导时间状语从句的用法 这三个词的意思很简单，都有“当……时候”的意思。但学生经常会问三个词的区别在哪儿，特别是在做选择题的时候。别说是学生，就我个人而言，做这样的选择题要保证百分之百的 正确也是不可能的。现根据大量的实例和个人的思考，做一点小结，供大家参考。 一、when 的用法 如果只从现象来看，when 从句用的最多的是一般过去时，而主句的时态没有限制，根据具 体情况而定。 When he was a child he was always trying out new ideas. 他小时候就常常试验一些新的设想。 when she came into my room I was just reading a book. 她走进我房间时，我正在看书。 Were you writing when the teacher came in? 老师进来的时候，你在写信吗？ Sorry，I was out when you called me. 对不起，你打电话来的时候我出去了。 He was on the point of leaving when someone knocked at the door. 他正要走,这时有人敲门。 I thought of it just when you opened your mouth. 就在你要说话的时候,我也想到了。 I had hardly[scarcely] closed my eyes when someone knocked at the door. 我刚一闭上眼，就有人在敲门了。 根据以上的例句，我们可以总结出一点：when 从句的A事件，相当于另一个事件B发生的时间点。也就是说，when 从句的重点不在动作本身发生的状态，而只是把它作为一个时间 点，所以when 多数情况下用的是一般过去时，则不用正在进行时。因为如果用正在进行时，它表示的就是一段时间而不是一个时间点了。根据这一点，有的文章补充说：when 从句的动词大多是瞬时动词。这种说法也可以参照。 实际上，when 从句也可以有其它的时态，但几乎也不用进行时，因为它也只是作为一个时 间参照点。例如： When I got to the airport，the guests had left. 当我赶到飞机场时，客人们已经离开了。 When he had finished his homework，he took a short rest． 当他完成作业后，他休息了一会儿。 Why do you want a new job when you have got such a good one already？ 你已经找到如此好的工作，为何还想再找新的？ You shall borrow the book when I have finished reading it.