十六烷基三甲基氯化铵在β-环糊精水溶液中的胶束化行为

Micellization Behavior of Cetyltrimethylammonium Chloride in Aqueous β-Cyclodextrin Solutions

通过测定十六烷基三甲基氯化铵 (CTAC) +H2 O和CTAC + β 环糊精 (β CD) +H2 O体系在 2 98.15K时的电导和密度 ,计算了一系列重要的热力学参数 ,如临界胶束浓度、胶束离解度、CTAC分子碳链从 β 环糊精水溶液到胶束的转移自由能、CTAC的标准偏摩尔体积以及CTAC和 β CD形成的包络物的计量比和包络常数等 .结果表明 ,β CD对CTAC的胶束化有较显著的影响 .由于CTAC的疏水碳链被 β CD空腔包络 ,CTAC的热力学活度降低 ,削弱了其胶束的生成 .但是 ,β CD及其包络物基本上不参与CTAC胶束的生成 ,而且一旦胶束形成 ,包络物对CTAC的胶束性质也没有明显的影响 .在简单模型的基础上 ,计算了CTAC分子碳链进入 β CD疏水空腔的CH2 基团的数目 ,从另一方面证明 β CD与CTAC分子形成了包络物 ,当β CD的浓度较高时 ,包络物的计量比为 2∶1.

Molar volume and conductivity measurements have been carried out at 298.15 K for ~cetyltr^imeth^ylammo^nium chloride (CTAC)+H 2O and CTAC+β-cyclodextrin (β-CD)+H 2O systems. The apparent critical micelle concentrations, the dissociation degree of the micelle, the transfer free energy for the hydrocarbon chain of CTAC from aqueous β-CD solutions to the micelle, the standard partial molar volumes of CTAC in aqueous β-CD solutions, the stoichoimetry and the equilibrium constants for the inclusion compounds of CTAC with β-CD have been determined. The influence of β-CD and its complexes on the micellization process of CTAC is analyzed. It is shown that β-CD partly screened the hydrophobic hydrocarbon chain of CTAC molecules from contact with the surrounding medium and retarded the formation of CTAC micelles in a certain extent. However, β-CD and its complexes do not participate in the formation of CTAC micelles, and the complexes have no significant effect on the micelle properties once the micelles are formed. The number of CH 2 groups entering the cavity of β-CD was calculated based on a simple model. The result suggests that β-CD forms inclusion compounds with CTAC, and the stoichoimetry is found to be 2∶1 at higher concentrations of β-CD.