Gravity-induced phase phenomena in plate-rod colloidal mixtures

TL;DR

This paper develops a theoretical framework to understand gravity's influence on phase phenomena in colloidal plate-rod mixtures, enabling better interpretation of sedimentation experiments and predicting phase behavior changes.

Contribution

It introduces a sedimentation path theory that incorporates gravity into microscopic models, allowing disentanglement of gravity effects from bulk phase behavior in colloidal mixtures.

Findings

Reproduces experimental observations of five mesophases.

Shows how sample height and buoyant mass ratio control phase sequences.

Provides predictions for experimental testing of phase behavior.

Abstract

Gravity can affect colloidal suspensions since for micrometer-sized particles gravitational and thermal energies can be comparable over vertical length scales of a few millimeters. In mixtures, each species possesses a different buoyant mass, which can make experimental results counter-intuitive and difficult to interpret. Here, we revisit from a theoretical perspective iconic sedimentation-diffusion-equilibrium experiments on colloidal plate-rod mixtures by van der Kooij and Lekkerkerker. We reproduce their findings, including the observation of five different mesophases in a single cuvette. Using sedimentation path theory, we incorporate gravity into a microscopic theory for the bulk of a plate-rod mixture. We also show how to disentangle the effects of gravity from sedimentation experiments to obtain the bulk behavior and make predictions that can be experimentally tested. These include changes in the sequence by altering the sample height. We demonstrate that both buoyant mass ratio and sample height form control parameters to study bulk phase behavior.