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柱状纳米孔中聚集吸附的影响。虽然近年来在理解表面活性剂在开放的平面上的自组装方面取得了很大的进展，但对限制效应和曲率效应对狭孔中聚集吸附的意义知之甚少。这些问题将通过研究烷基乙氧基化物(CnEn.)和烷基葡萄糖苷(CnGx.)不同烷基链长和不同头基大小的表面活性剂在MCM-41和SBA-15型介孔二氧化硅中形成六方有序的圆柱孔阵列，圆柱孔的大小均匀(孔径为3-12 nm)。流动吸附微量热法将被用来确定作为孔填充程度的函数的微分摩尔吸附热和吸附熵，从而提供表面活性剂聚集体在孔中状态的完整热力学表征。此外，色层脉冲实验将提供一些关于表面活性剂的吸附动力学的信息。实验计划的细节将与这一合作项目的两个合作小组共同规划，其中将通过计算机模拟研究表面活性剂在纳米孔中聚集的静态(Gubbins)和动态(Schoen/Klapp)方面。这些模拟研究的结果将为解释该项目的实验结果提供依据。

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.