Formation of periodic size-segregated stripe pattern via directed self-assembly of binary colloids and its mechanism

Abstract

Convective self-assembly, well known for producing highly ordered monolayer structures, has been used in this study to create novel surface patterns using the binary mixture of colloids. We demonstrate that different patterns form, based on the size ratio (Small/Large) of the particles, and particles volume ratio. Surprisingly, certain binary particle mixtures resulted in spontaneous size based segregation. In some cases, the particle separation occurred along the direction of the meniscus contact line, and by the mere design of the process, we created periodic stripe patterns with controlled width. The particle volume fraction, size differences, surface tension, and the curvature of the meniscus played a crucial factor in the segregation process as well as in determining the width of each of the stripes. Furthermore, based on both empirical and numerical analysis, a mechanism for size-based segregation of particles via directed self-assembly is proposed.