第24卷第2期化學(xué)研究與應(yīng)用Vol 24. No. 22012年2月Chemical reFeb.,2012文章編號(hào):1004-1656(2012)02032205乙二醇對(duì)烷基三甲基溴化銨膠團(tuán)化行為的影響凌錦龍,徐敏虹,洪迪,張艷(湖州師范學(xué)院生命科學(xué)學(xué)院浙江湖州313000摘要:利用電導(dǎo)法研究了烷基三甲基溴化銨表面活性劑(CTAB,n=12,14,16),即十二烷基三甲基溴化銨(DTAB),十四烷基三甲基溴化銨(TAB)和十六烷基三甲基溴化銨(CTAB)在混合極性溶劑乙二醇/水(體積分?jǐn)?shù)0~40%)中的膠團(tuán)化行為?？疾炝藴囟葘?duì)膠團(tuán)形成的影響,應(yīng)用相分離模型估算了三個(gè)表面活性劑的膠團(tuán)熱力學(xué)參數(shù)。結(jié)果表明臨界膠團(tuán)濃度(cme)和反離子解離度(a)都隨乙二醇組分的增加而增大。在二醇/水混合溶劑中膠團(tuán)形成的標(biāo)準(zhǔn)吉布斯自由能相差很小混合焓都是負(fù)值,而混合熵都為正值,說(shuō)明熵補(bǔ)償效應(yīng)在膠團(tuán)形成中起主導(dǎo)作用。關(guān)鍵詞烷基三甲基溴化銨;乙二醇/水混合溶劑;臨界膠團(tuán)濃度;膠團(tuán)熱力學(xué)中圖分類號(hào):06472文獻(xiàn)標(biāo)識(shí)碼:AEffect of ethylene glycol on the micellization behavior ofalkyltrimethylammonium bromidesLING Jin-long, XU Min-hong, HONG Di, ZHANG Yan( Institute of Life Sciences, Huzhou Teachers College, Huzhou 313000, ChinaAbstract: The micellization behavior of alkyltrimethylammonium bromides, viz, dodecyl-, tetradecyl-and hexadecyltrimethylammonim bromide( DTAB, TTAB and CTAB, respectively )in ethylene glycol(EG ) and water mixtures with varying volume fraction of EG(o/o)has been investigated employing electrical conductivity. Temperature dependence of the critical micelle concentration( cmc)wEScellar thermodynamics of these systems. The phase separation model of micellar formation w.applied to obtain the thermodynamic parameters of micellization. It is showed that the cmc and the degree of counterion dissociation(a)increase with increasing content of EG in mixed solvent. There are small differences in the standard molar Gibbs free energies ofmicellization over the temperature range investigated. The enthalpy of micellization is negative in all cases, whereas the entropy is always positive. This behavior indicates that an enthalpy-entropy compensation effect is the goveming factor for micellization.Key words: alkyltrimethylammonium bromide; EG and water binary mixture; critical micelle concentration; micellar thermody在混合溶劑中研究表面活性劑的熱力學(xué)性途徑:1)與表面活性劑分子的相互作用,2)改變?nèi)苜|(zhì)有助于理解溶質(zhì)溶質(zhì)和溶質(zhì)溶劑的相互作劑的特性。改變?nèi)芤罕倔w相性質(zhì)最方便的辦法就表面活性劑膠束性質(zhì)主要由復(fù)雜的親水是添加有機(jī)溶劑。有機(jī)溶劑主要進(jìn)入本體相而不和憎水間平衡所決定。而溶劑因素的影響有兩條參與膠團(tuán)的形成這此右卻派加劑通常要求具有中國(guó)煤化工CNMHG收稿日期:20101128;修回日期:2011027聯(lián)系人簡(jiǎn)介:凌錦龍(1964-)男副教授主要從事溶液熱力學(xué)和界面化學(xué)研究。 E-mail: lingiinlong@huc可第2期凌錦龍等:乙二醇對(duì)烷基三甲基決化銨膠團(tuán)化行為的影響很高的內(nèi)聚能和介電常數(shù),以及較高的氫鍵形成40%的水溶液中的電導(dǎo)率;在20%EG溶液中測(cè)能力。二元醇具有兩個(gè)羥基,既能形成分子內(nèi)氫定了三種表面活性劑在29815K-31815K時(shí)的鍵,也能與水形成氫鍵而構(gòu)成三維網(wǎng)狀結(jié)構(gòu)。其電導(dǎo)率。圖1是298.15K時(shí)CTAB電導(dǎo)率隨EG對(duì)表面活性劑膠團(tuán)形成的影響已引起基礎(chǔ)研究濃度的變化關(guān)系(其他未列出)?？梢钥闯?電導(dǎo)者的廣泛興趣1。 Palepu1等研究了 Triton x.率在膠團(tuán)形成前后有一個(gè)突變兩條直線的交點(diǎn)100在二元醇(乙二醇,三甘醇四甘醇)水溶液中即為cmc,而膠團(tuán)形成之后的直線斜率與之前的直的自聚行為及膠團(tuán)熱力學(xué)性質(zhì)。Easm等研究線斜率之比即為反離子解離度a。表1和表2列了在水乙二醇和水1,3-丙二醇混合溶劑中表面出了三種表面活性劑的cme和反離子解離度aa活性劑頭基對(duì)聚集行為的影響。這些研究指出了非離子或離子表面活性劑在有二元醇存在時(shí)的不同的膠團(tuán)行為,說(shuō)明了本體相在膠團(tuán)形成過(guò)程中的重要性,揭示了通過(guò)改變本體相性質(zhì)來(lái)控制膠50團(tuán)聚集的可能性1。本文選擇不同疏水鏈長(zhǎng)的烷基三甲基溴化銨CTAB,n=12,14,16),研究了在不同乙二醇含量水溶液中的膠團(tuán)化行為,分析了溫度對(duì)膠團(tuán)形成圖1298.15K時(shí)不同體積分敷的乙二醇水溶液中的影響,探討了極性有機(jī)溶劑的加入對(duì)膠團(tuán)形成CTAB電導(dǎo)率隨濃度變化關(guān)系的影響規(guī)律。Fig 1 Conductivity versus concentration of CTAB inEG+H,0 mixtures at 298 15K1實(shí)驗(yàn)部分由表1可以看到,cm隨EG的增加而增加。1.1試劑這主要由兩個(gè)因素引起:1)EG的加入,降低了本十二烷基三甲基溴化銨(DTAB),十四烷基三體相的內(nèi)聚能密度因而增加了表面活性劑單體甲基溴化銨(TTAB),十六烷基三甲基溴化銨的溶解性,使cme升高2)助溶劑引起水的介電常(CTAB),AR,用丙酮乙醚混合溶劑重結(jié)晶5次;數(shù)下降導(dǎo)致離子頭基間的相互斥力增加,使cmc乙二醇(EG),AR;水為去離子水經(jīng)石英亞沸重蒸升高)。處理,電導(dǎo)率為10yS所用試劑經(jīng)測(cè)定表溫度對(duì)臨界膠團(tuán)濃度的影響,可以從表2看面張力曲線均無(wú)最低點(diǎn)表明無(wú)高活性雜質(zhì)存在。出。當(dāng)固定溶劑比例時(shí)表面活性劑的cmc隨溫1.2電導(dǎo)實(shí)驗(yàn)度升高而升高。這里存在兩個(gè)對(duì)立的影響因素:D11A型電導(dǎo)率儀,上海精密科學(xué)儀器有)升高溫度,表面活性劑親水基團(tuán)的水合能力下限公司雷磁儀器廠。電導(dǎo)測(cè)定在帶有恒溫水夾套降,這有助于膠團(tuán)的形成:)升高溫度同時(shí)也導(dǎo)致的容器中進(jìn)行。溫度控制精度為土0.IK。測(cè)得表面活性劑疏水基周圍水結(jié)構(gòu)的破壞這不利于29815K時(shí)水中CTAB臨界膠束濃度(cm)9.3x膠團(tuán)形成。從結(jié)果來(lái)看第二個(gè)因素起了主導(dǎo)作104mol·L,與文獻(xiàn)值相符。用同時(shí)由表1和表2看出對(duì)膠團(tuán)溶液的反離2結(jié)果與討論子解離度α,增加EG含量與升高溫度的效應(yīng)是一致的,都是增大。部分原因可能由于膠團(tuán)聚集數(shù)2.1臨界膠團(tuán)濃度cme下降從而導(dǎo)到測(cè)定了29815K時(shí)DAB,TAB和CTAB在的。THa中國(guó)煤化工降而造成CNMHG乙二醇體積分?jǐn)?shù)分別為0%,10%,20%,30%和324化學(xué)研究與應(yīng)用第24卷表129815K時(shí)烷基三甲基溴化銨在乙二醇水溶液中的cmea,△和△CTable 1 The cme, degree of counterion dissociation(a), Gibbs energy of micellization( AG. )and Gibbs energy oftransfer( AG )for alkyltrimethylammonium bromides in EG aqueous solution at 298. 15 kcmc/10a-△c/kJ·mol-1△G。/kJ·molDTAB00.2531016.910.2600.7919.010.2811.710.32032.55TTAB03.8141.804.1900004.650.2651.436.080.28738.728.860.31636.49CTAB0.931.1846.220.27045.2.133.736.23衰2不同溫度下烷基三甲基溴化銨在20%EG水溶液中的cm,a,及膠團(tuán)熱力學(xué)參數(shù)Table 2 The cmc, degree of counterion dissociation(a)and thermodynamic parameters ofmicellization for alkyltrimethylammonium bromides in 20%EG aqueous solution at various temperaturesT/Kcmc/103mol·L1AG/]. mol-△HJ·mlT△s/,molDTAB19.4414.57303.1533.7619.80308.1533.5113.33313.150.35412.69318.150.37932.9112.04TTAB298.150.2655.150.27640.3530.69308.155.770.2840.2531.518.74313.150.29840.107.77318.157.400.3126.74CTAB98.150.27045.4430.0515.39303.150.27845.4830.9214.570.28745.4931.7813.71313.1545.4632.6712.80318.1533.5611.902.2膠團(tuán)熱力學(xué)Gibbs自中國(guó)煤化工混合熵△S。:由相分離模型可得到膠團(tuán)形成的標(biāo)準(zhǔn)摩爾CNMH(1)第2期凌錦龍等:乙二醇對(duì)烷基三甲基澳化銨膠團(tuán)化行為的影響325AHm=-(2-@)RT(ain eme(2)基從本體相向膠團(tuán)的遷移更為困難?！鰿越大,cmc也越高。表2數(shù)據(jù)表明,在同一EG濃度下,混合自由T2AS。=△-△3)能隨溫度的變化很小,幾乎不變.隨烷基鏈碳原式中a是反離子解離度,X是用摩爾分?jǐn)?shù)表示子數(shù)目的增加,△c變得更負(fù),即膠團(tuán)形成的自發(fā)的cmc濃度。從cmc隨溫度的變化關(guān)系可以求出性增大,所以相應(yīng)的cmc也降低。膠團(tuán)混合焓都△H。圖2為各表面活性劑nxm隨溫度的變化是負(fù)值隨溫度增加而降低,混合熵都是正值,也關(guān)系均為線性關(guān)系這與文獻(xiàn)2的結(jié)論一致。隨溫度增加而降低。這說(shuō)明了在20%EG水溶液為考察共溶劑對(duì)膠團(tuán)化過(guò)程的影響,引人了中,烷基三甲基溴化銨的膠團(tuán)化行為并不是熵驅(qū)遷移自由能△C動(dòng)而是焓熵補(bǔ)償效應(yīng)的結(jié)果。 Callaghan(在研究EG水溶液中溴代十六烷基吡啶聚集行為時(shí),認(rèn)為在高濃度的EG水溶液中(富醇區(qū)),隨溫度升▲CTA髙混合焓△F變小,而熵變?chǔ)從正變?yōu)樨?fù),因此△B是膠團(tuán)形成的驅(qū)動(dòng)力。Rui219研究了在20%(wt)EC水溶液中(富水區(qū)),認(rèn)為膠團(tuán)化過(guò)程仍然是在與水結(jié)構(gòu)性質(zhì)類似的環(huán)境中進(jìn)行的,EG的加295300305310315320入僅僅產(chǎn)生很小的溶質(zhì)溶劑相互作用,膠團(tuán)形成主要是焓熵補(bǔ)償效應(yīng)。Le2在研究EG水溶液圖2在20%EG水溶液中烷基三甲基決化銨ln隨溫度的變化關(guān)系中SDS的聚集行為時(shí)也有相似的結(jié)論。溫度的升Fig 2 Plot of Inx versus temperature for高,主要是弱化了氫鍵形成能力和液體的結(jié)構(gòu)化,alkyltrimethylammonium bromides in20% EG aqueous solut導(dǎo)致溶液的極性降低,疏溶劑作用減弱,使表面活性劑離子頭基間的斥力增加,延緩膠團(tuán)的形成,△C=(△Ce)s1o-(△C。)時(shí)4(4)cme增大。計(jì)算結(jié)果一并列于表1和表2中。由表1的膠團(tuán)熱力學(xué)參數(shù)來(lái)看,△C都為負(fù)3結(jié)論值,說(shuō)明膠團(tuán)的形成是自發(fā)的。隨EG濃度的增加,△C也呈增加趨勢(shì),因此EG的加人不利于膠烷基三甲基溴化銨的cmc和反離子解離度a團(tuán)的形成。膠團(tuán)cmc隨本體相組成的變化原則上都隨混合溶劑中EG濃度的增加而增大。升高溫由遷移自由能△C決定從水到乙二醇+水混合度的影響與添加乙二醇的效應(yīng)一致。在EG水溶物的遷移自由能的大小取決于水、有機(jī)溶劑以及液中,膠團(tuán)形成的驅(qū)動(dòng)力是增熵補(bǔ)償效應(yīng)。隨著水有機(jī)溶劑的相互作用1?！鰿m都是正值是溫度升高混合溶液極性降低疏水作用減弱延因?yàn)镋G的加入,導(dǎo)致疏水鏈溶解性增大,致使尾緩膠團(tuán)形成。參考文獻(xiàn):[1]Binana-Limbele W, Zana R. 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