Self-Assembly of Surfactants in Nanopores: A Thermodynamic Study of Confinement and Curvature Effects

本项目旨在研究约束和曲率对非离子表面活性剂在圆柱形纳米孔中聚集吸附的影响。尽管近年来对表面活性剂在开放平面上的自组装的理解取得了很大进展，但对限制效应和曲率效应对窄孔中聚集吸附的重要性知之甚少。这些问题将通过研究不同烷基链长度和头基团大小的烷基乙氧基酸酯（CnEn.）和烷基糖苷（CnGx.）表面活性剂在MCM-41和SBA-15型介孔二氧化硅上的吸附来研究。MCM-41和SBA-15型介孔二氧化硅构成尺寸均匀（孔径3 ~ 12nm）的六边形有序柱状孔阵列。流动吸附微量热法将用于确定作为孔隙填充程度函数的微分摩尔焓和吸附熵，从而提供表面活性剂聚集在孔隙中的状态的完整热力学表征。此外，色谱脉冲实验将得到一些关于表面活性剂吸附动力学的信息。实验计划的细节将与该合作项目的两个合作小组共同规划，其中静态（Gubbins）和动态（Schoen/Klapp）方面的表面活性剂在纳米孔中的聚集将通过计算机模拟进行研究。这些模拟研究的结果将为本项目实验结果的解释提供基础。

This project aims at investigating the effects of confinement and curvature on the aggregative adsorption of nonionic surfactants in cylindrical nanopores. Whereas much progress has been made in recent years towards an understanding of the self-assembly of surfactants on open flat surfaces, little is known about confinement effects and the significance of curvature effects on the aggregative adsorption in narrow pores. These questions will be investigated by studying the adsorption of alkyl ethoxylate (CnEn.) and alkyl glucoside (CnGx.) surfactants of different alkyl chain length and head group sizes in MCM-41 and SBA-15 type mesoporous silicas, which constitute hexagonally ordered arrays of cylindrical pores of uniform size (3 to 12 nm pore diameter). Flow adsorption microcalorimetry will be used to determine the differential molar enthalpies and entropies of adsorption as a function of the degree of pore filling, thus providing a full thermodynamic characterization of the state of surfactant aggregates in the pores. In addition, chromatographic pulse experiments will yield some information about the adsorption kinetics of the surfactants. Details of the experimental program will be planned jointly with the two partner groups of this collaborative project, where static (Gubbins) and dynamic (Schoen/Klapp) aspects of surfactant aggregation in nanopores will be studied by computer simulations. The results of these simulation studies will provide a basis for an interpretation of the experimental results of this project.