Department of Physics, University of Surrey , Guildford GU2 7XH, United Kingdom.
Langmuir. 2017 May 16;33(19):4796-4805. doi: 10.1021/acs.langmuir.7b00946. Epub 2017 May 2.
We investigate the drying process of three-component and polydisperse colloidal suspensions using Brownian dynamics simulations. We have previously reported (Phys. Rev. Lett. 2016, 116, 118301) on the drying of binary mixtures. For binary mixtures, we found that a gradient of colloidal osmotic pressure develops during drying and that this leads to the final film being stratified with a layer of smaller particles on top of a layer of larger particles. Here, we find that stratification by size is very general and also occurs in ternary and polydisperse mixtures. We name the segregation effect colloidal diffusiophoresis. In particular, we show that by changing the composition of a ternary mixture, different stratification morphologies can be achieved and hence the film properties can be tuned. In polydisperse spheres, colloidal diffusiophoresis leads to enrichment in the large particles at the bottom part of the film, whereas the top part is enriched with smaller particles. This segregation means that in the final film, the particle size distribution depends on height. Thus, the properties of the film will then depend on height. We propose a model that predicts a power-law dependence of the phoretic velocity on particle size. Results from the model and simulation show a good agreement.
我们使用布朗动力学模拟研究了三元和多分散胶体悬浮液的干燥过程。我们之前曾报道过（Phys. Rev. Lett. 2016, 116, 118301）关于二元混合物的干燥情况。对于二元混合物，我们发现胶体渗透压的梯度在干燥过程中会发展，这导致最终的薄膜分层，上面是一层较小的颗粒，下面是一层较大的颗粒。在这里，我们发现分层现象非常普遍，在三元和多分散混合物中也会发生。我们将这种分离效应命名为胶体扩散泳。特别是，我们表明通过改变三元混合物的组成，可以实现不同的分层形貌，从而可以调整薄膜的性质。在多分散球体中，胶体扩散泳导致大颗粒在薄膜的底部富集，而顶部则富集了较小的颗粒。这种分离意味着在最终的薄膜中，颗粒尺寸分布取决于高度。因此，薄膜的性质将取决于高度。我们提出了一个模型，预测了扩散泳速度与颗粒尺寸的幂律关系。模型和模拟的结果显示出很好的一致性。
