Investigation of relationship between flow pattern and phase separation structure in a liquid mixture layer using EHD convecttion

研究了聚合物共混膜中基于电流体动力学（EHD）对流的流型与相分离结构的关系。本研究采用溶剂蒸发和热淬灭的方法来诱导共混膜中的相分离，研究了EHD对流对聚苯乙烯（PS）/聚醋酸乙烯酯（PVA）共混膜中微区结构的影响，以证明EHD效应作为共混膜中混合和形态控制手段的可行性。在这里，聚合物-甲苯溶液被散布在具有图案化电极的玻璃基板上以施加直流电场，并且在聚合物溶液中形成了良好定义的EHD对流结构。结果，在PS/PVA聚合物共混物中形成规则图案，其中富含PVA的区域被限制在图案化电极的每个单元内，即，在正电极和负电极之间，在适当的电压下。在SiO_2覆盖的玻璃衬底上进行的实验表明，这种新的形貌不是由于聚合物组分对沉积在玻璃衬底上的Pt电极的润湿/去润湿效应造成的，在后者的情况下，由于实验装置和过程中的一些问题，不幸的是，我们不能得到有效的结果。基于考虑流体力学效应的Cahn-Hilliard模型，开发了相分离的数值模拟程序，阐明了毛细力、重力和温度梯度对相分离结构的影响。

We have investigated the relationship between the flow pattern based on electrohydrodynamic (EHD) convection and phase separation structure in a polymer blend film. In the present study, the solvent evaporation and thermal quench of polymer blend solutions were adopted to induce the phase separation in the film.In the former method, we have investigated the effect of EHD convection on the domain structure in a polystyrene (PS)/polyvinylacetate (PVA) blend film to demonstrate the feasibility of using the EHD effect as a means of mixing and morphology control in a polymer blend film. Here, polymers-toluene solutions were spread on a glass substrate with patterned electrodes to apply a dc electric field, and well-defined structures of EHD convection were formed in the polymer solutions. As a result, regular patterns were formed in the PS/PVA polymer blend him in which PVA-rich domains were confined within each unit of patterned electrodes, i.e.,between positive and negative electrodes, at an appropriate electric voltage. Also, it was demonstrated that such novel morphology are not due to the wetting/dewetting effect of polymer components to the Pt electrodes deposited on the glass substrate, by experiments with a SiO_2-covered substrate.In the later case, since we had some problems in the experimental apparatus and procedure, unfortunately we could not obtain the available results.In addition, we have developed the numerical simulation code of the phase separation based on the Cahn-Hilliard model with a hydrodynamic effect, and then clarified the effects of the capillary force, gravity force and temperature gradient on the phase separation structure.