Sedimentation stacking diagram of binary colloidal mixtures and bulk phases in the plane of chemical potentials

TL;DR

This paper presents a comprehensive theory linking bulk phase diagrams of binary colloidal mixtures to their sedimentation stacking sequences under gravity, revealing complex behaviors influenced by sample height and mixture composition.

Contribution

The paper introduces a detailed theoretical framework that connects bulk phase diagrams to sedimentation stacking sequences, including a catalog of generic phase diagrams for practical use.

Findings

Sedimentation paths in chemical potential space determine stacking sequences.

Stacking diagrams can be very complex, especially with finite sample height.

The theory applies to mixtures of polymers and colloids and generalizes to multiple components.

Abstract

We give a full account of a recently proposed theory that explicitly relates the bulk phase diagram of a binary colloidal mixture to its phase stacking phenomenology under gravity [Soft Matter 9, 8636 (2013)]. As we demonstrate, the full set of possible phase stacking sequences in sedimentation-diffusion equilibrium originates from straight lines (sedimentation paths) in the chemical potential representation of the bulk phase diagram. From the analysis of various standard topologies of bulk phase diagrams, we conclude that the corresponding sedimentation stacking diagrams can be very rich, even more so when finite sample height is taken into account. We apply the theory to obtain the stacking diagram of a mixture of nonadsorbing polymers and colloids. We also present a catalog of generic phase diagrams in the plane of chemical potentials in order to facilitate the practical application of our concept, which also generalizes to multi component mixtures.