Spontaneous evolution of self-assembled phases from anisotropic colloidal dispersions

TL;DR

This study explores the spontaneous phase evolution and aging dynamics of high-aspect ratio nanoclay dispersions, revealing new phase separation and gelation behaviors over 3.5 years, and establishing a detailed phase diagram.

Contribution

First comprehensive phase diagram for aging Montmorillonite dispersions in salt-free conditions, highlighting distinct phase separation and gelation pathways.

Findings

Discovered stable sols that evolve into networks via phase separation or gelation.

Identified equilibrium fluid and gel phases in the phase diagram.

Detected interconnected network structures through rheology measurements.

Abstract

We investigate the spontaneous evolution of various self-assembled phase states from a homogeneous aqueous dispersion of high-aspect ratio Montmorillonite (Na Cloisite) nanoclay platelets grounded on the observations made over a period of 3.5 years. We have established the tw-c phase diagram for this system for the first time in salt-free suspensions under normal pH conditions using rheology experiments and have detected that these suspensions do undergo nontrivial phase evolution and aging dynamics. Distinctive phase separation, equilibrium fluid and equilibrium gels in the tw-c phase space are discovered. Cole-Cole plots derived from rheology measurements suggested the presence of inter connected network-like structures for c > cg, cg being the gelation concentration. All dispersions formed stable sols during the initial time, and with aging network-like structures were found to form via two routes: one for c < cg, by phase separation and another for c > cg, through equilibrium gelation. This has invoked and called for a revisit of the phase diagram of aging MMT dispersions.