Goldsipe Arthur, Blankschtein Daniel
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Langmuir. 2005 Oct 25;21(22):9850-65. doi: 10.1021/la050699s.
A predictive molecular-thermodynamic theory is developed to model the effect of counterion binding on micellar solution properties of binary surfactant mixtures of ionic and nonionic (or zwitterionic) surfactants. The theory combines a molecular-thermodynamic description of micellization in binary surfactant mixtures with a recently developed model of counterion binding to single-component ionic surfactant micelles. The thermodynamic component of the theory models the equilibrium between the surfactant monomers, the counterions, and the mixed micelles. The molecular component of the theory models the various contributions to the free-energy change associated with forming a mixed micelle from ionic surfactants, nonionic (or zwitterionic) surfactants, and bound counterions (referred to as the free energy of mixed micellization). Specifically, the various molecular contributions to the free energy of mixed micellization model the underlying physics associated with the assembly of, and the interactions between, the surfactant polar heads, the surfactant nonpolar tails, and the bound counterions. Utilizing known structural characteristics of the surfactants and the counterions, along with the solution conditions, the free energy of mixed micellization is minimized to predict various optimal micelle characteristics, including the degree of counterion binding, the micelle composition, and the micelle shape and size. These predicted optimal micelle characteristics are then used to predict the critical micelle concentration (cmc) and the average micelle aggregation number. Our predictions of the degree of counterion binding, the cmc, and the average micelle aggregation number show good agreement with available experimental results from the literature for several binary surfactant mixtures. In addition, the theory is used to shed light on the relationship between the micelle composition, counterion binding and ion condensation, and the micelle shape transition.
建立了一种预测性分子热力学理论，以模拟抗衡离子结合对离子型与非离子型（或两性离子型）表面活性剂二元混合物胶束溶液性质的影响。该理论将二元表面活性剂混合物中胶束形成的分子热力学描述与最近开发的抗衡离子与单组分离子型表面活性剂胶束结合的模型相结合。该理论的热力学部分对表面活性剂单体、抗衡离子和混合胶束之间的平衡进行建模。该理论的分子部分对由离子型表面活性剂、非离子型（或两性离子型）表面活性剂和结合的抗衡离子形成混合胶束所涉及的自由能变化的各种贡献进行建模（称为混合胶束化自由能）。具体而言，混合胶束化自由能的各种分子贡献对与表面活性剂极性头、表面活性剂非极性尾和结合的抗衡离子的组装及相互作用相关的基础物理过程进行建模。利用表面活性剂和抗衡离子的已知结构特征以及溶液条件，使混合胶束化自由能最小化，以预测各种最佳胶束特性，包括抗衡离子结合程度、胶束组成以及胶束形状和大小。然后，这些预测的最佳胶束特性用于预测临界胶束浓度（cmc）和平均胶束聚集数。我们对抗衡离子结合程度、cmc和平均胶束聚集数的预测与文献中几种二元表面活性剂混合物的现有实验结果显示出良好的一致性。此外，该理论用于阐明胶束组成、抗衡离子结合与离子凝聚以及胶束形状转变之间的关系。
