Margination regimes and drainage transition in confined multicomponent suspensions

TL;DR

This paper develops a mechanistic theory for segregation in confined multicomponent suspensions, identifying regimes of margination and a critical drainage transition driven by hydrodynamic interactions and wall effects.

Contribution

It introduces a new theoretical framework that captures margination regimes and predicts a sharp drainage transition in multicomponent suspensions.

Findings

Identification of multiple segregation regimes depending on the margination parameter

Prediction of a critical drainage transition where one component depletes from the bulk

Simulation results confirming the transition with changes in particle size or flexibility

Abstract

A mechanistic theory is developed to describe segregation in confined multicomponent suspensions such as blood. It incorporates the two key phenomena arising in these systems at low Reynolds number: hydrodynamic pair collisions and wall-induced migration. In simple shear flow, several regimes of segregation arise, depending on the value of a "margination parameter" M. Most importantly, there is a critical value of M below which a sharp "drainage transition" occurs: one component is completely depleted from the bulk flow to the vicinity of the walls. Direct simulations also exhibit this transition as the size or flexibility ratio of the components changes.