Self-Assembly of surfactants in nanopores: a dissipative particle dynamics study

耗散粒子动力学(DPD)是近年来发展起来的一种研究大分子自组装体系动力学过程的强大而通用的计算机模拟技术。我们计划应用DPD来研究接近固体表面的水-表面活性剂混合物中胶束的形成动力学，或在理想介孔介质中，如MCM-41类型的材料。为了获得相应的长度和时间尺度，分别约为100纳米和1微米S，表面活性剂和水分子都是在粗粒模型的基础上描述的；然后，所产生的“有效粒子”之间的保守力被反映存在快速变化的内部自由度的随机和耗散力补充。本项目的重点是了解固体表面和纳米孔中强两亲分子的临界表面聚集浓度(CSAC)附近的单粒子和集体动力学。在实验上，当浓度略高于CSAC时，吸附过量的急剧增加归因于表面诱导胶束的形成。这些聚集体的形状和大小被怀疑不仅强烈地取决于表面活性剂本身的结构，而且还取决于亲水性的程度和(特别是在狭窄的孔隙中)孔壁的曲率。通过DPD计算机模拟，研究了胶束形成的动力学及其与约束衬底性质的相互作用。热力学和结构特征在本应用程序包的实验(Findenegg)和理论(Gubbins)项目中进行了探索。

In recent years dissipative particle dynamics (DPD) has been established as a powerful and versatile computer simulation technique by which dynamical processes in macromolecular self-assembling systems can be studied. We plan to apply DPD to investigate the dynamics of micelle formation in water-surfactant mixtures near solid surfaces or in idealized mesoporous media like MCM-41-type of materials. In order to access the relevant length and time scales of about 100 nm and 1 µs, respectively, both surfactant and water molecules are described on the basis of coarse-grained models; conservative forces between the resulting "effective particles" are then supplemented by stochastic and dissipative forces reflecting the presence of rapidly varying internal degrees of freedom. The focal point of the present project is to understand single-particle and collective dynamics in the vicinity of the critical surface aggregation concentration (CSAC) of strong amphiphiles at solid surfaces and in nanopores. Experimentally, the sharp increase of the adsorption excess for concentrations slightly above the CSAC is ascribed to surface-induced micelle formation. Shape and size of these aggregates are suspected to strongly depend not only on the architecture of the surfactant itself, but also on the degree of hydrophility and (particularly in narrow pores) on the curvature of the pore walls. By means of DPD computer simulations the dynamics of the micelle formation and its interplay with properties of the confining substrate are investigated. Thermodynamic and structural features are explored in the experimental (Findenegg) and theoretical (Gubbins) projects of this application package.