Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom.
J Chem Phys. 2018 Apr 7;148(13):134909. doi: 10.1063/1.5022243.
I model the drying of a liquid film containing small and big colloid particles. Fortini et al. [Phys. Rev. Lett. 116, 118301 (2016)] studied these films with both computer simulation and experiment. They found that at the end of drying, the mixture had stratified with a layer of the smaller particles on top of the big particles. I develop a simple model for this process. The model has two ingredients: arrest of the diffusion of the particles at high density and diffusiophoretic motion of the big particles due to gradients in the volume fraction of the small particles. The model predicts that stratification only occurs over a range of initial volume fractions of the smaller colloidal species. Above and below this range, the downward diffusiophoretic motion of the big particles is too slow to remove the big particles from the top of the film, and so there is no stratification. In agreement with earlier work, the model also predicts that large Péclet numbers for drying are needed to see stratification.
我建立了一个模型，用于模拟含有小颗粒和大颗粒胶体的液膜干燥过程。Fortini 等人[Phys. Rev. Lett. 116, 118301 (2016)]通过计算机模拟和实验研究了这些薄膜。他们发现，在干燥的最后阶段，混合物发生了分层，小颗粒在大颗粒的顶部形成一层。我为这个过程开发了一个简单的模型。该模型有两个组成部分：在高密度下颗粒扩散的停止，以及由于小颗粒体积分数的梯度导致大颗粒的扩散迁移。该模型预测，分层仅在小胶体物质初始体积分数的范围内发生。在此范围之上和之下，大颗粒的向下扩散迁移太慢，无法将大颗粒从薄膜顶部移走，因此没有分层。与早期的工作一致，该模型还预测，需要大的干燥 Peclet 数才能观察到分层。
