Margination of bidisperse deformable droplets with thermal fluctuations.

Abstract

Margination is a shear-induced lateral segregation in confined flows, where particles of different size and deformability develop distinct distributions across the channel. While most existing mechanistic and simulation studies have focused on regimes dominated by flow, many emerging soft-matter and bioinspired systems operate at smaller scales where fluctuation-dissipation can compete with drift driven by shear. Here we simulate suspensions of deformable droplets with two sizes in planar Couette flow using dissipative particle dynamics (DPD) with a fluctuation-dissipation thermostat, which explicitly incorporates thermal fluctuations. By varying the droplet radius ratio <i>λ</i> and an operational Péclet number Pe based on the DPD thermostat coefficient, we quantify the steady segregation strength. Across the conditions examined here, large droplets preferentially migrate toward the channel center, whereas small droplets accumulate near the walls, and the segregation strengthens with increasing <i>λ</i>. These results show that DPD captures margination in fluctuation-affected regimes and that the trends can be organised by <i>λ</i> and the present thermostat-controlled Pe. This provides a compact basis for discussing sampling near the walls in confined soft suspensions, including soft carriers and microfluidic separations.