Statistical Mechanical Theory of the Coagel-Gel Phase Transition in Ionic Surfactant/Water Systems
Statistical Mechanical Theory of the Coagel-Gel Phase Transition in Ionic Surfactant/Water Systems
复制标题
离子表面活性剂/水体系中凝固凝胶-凝胶相变的统计力学理论
DOI：
10.1021/j100075a022
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
Toyoichi Tanaka
中科院分区：
文献类型：
--
作者：
M. Tsuchiya;K. Tsujii;K. Maki;Toyoichi Tanaka
一些离子表面活性剂/水体系经历凝胶-凝胶相变。凝胶和凝胶相均由表面活性剂和水的双层膜的交替层组成。烃链处于结晶状态，并且在凝固凝胶相中水层的厚度在10 A的数量级。在从凝胶转变为凝胶时，烃链变得能够围绕链轴旋转，并且水层的厚度不连续地增加到1000 A的数量级。我们提出了一个统计力学理论来解释这种相变。该系统的平均场吉布斯自由能被写成三阶参数的函数，这些参数与烃链的旋转运动、表面活性剂分子的抗衡离子的解离度以及相邻膜之间的距离有关。假设在烃链的旋转状态下，膜表面上的一个亲水性头部基团所占据的面积大于其固定状态下的面积。该理论成功地解释了烃链的无序相变和双层膜的同时分离。在一个分子的面积的扩展导致三阶参数之间的耦合。理论计算表明，这种耦合的强度导致三种类型的相变：（1）凝胶/凝胶相变，（2）假凝胶（烃链处于结晶状态，膜分离）/凝胶相变，（3）凝胶/假凝胶（烃链绕链轴的旋转被释放，膜不分离）相变。
Some ionic surfactant/water systems undergo the coagel-gel phase transition. Both coagel and gel phases consist of alternating layers of bilayer membranes of surfactants and water. The hydrocarbon chains are in a crystalline state, and thickness of water layer is in the order of 10 A in the coagel phase. Upon the transition from coagel to gel, the hydrocarbon chains become able to rotate around the chain axis, and the thickness of water layer discontinuously increases to the order of 1000 A. We present a statistical mechanical theory to explain this phase transition. The mean field Gibbs free energy of the system is written as a function of three-order parameters which are concerned with the rotational motion of the hydrocarbon chains, the degree of dissociation of counterions of the surfactant molecules, and the distance between neighboring membranes. The area occupied by one hydrophilic head group on the membrane surface in the rotating state of the hydrocarbon chain is assumed to be larger than that in its fixed state. The theory successfully explains theorder-disorder phase transition of the hydrocarbon chains and the simultaneous Separation of bilayer membranes. The expansion in the area of one molecule leads to a coupling between three-order parameters. The theoretical calculation predicts that the strength of this coupling results in the three types of phase transition:(1) coagel/gel phase transition,(2) pseudogel (the hydrocarbon chains are in crystalline state, and the membranes separate)/gel phase transition,(3) coagel/pseudocoagel (the rotation of hydrocarbon chains around the chain axis is released, and the membranes do not separate) phase transition.