Multiple nonergodic disordered states in Laponite suspensions: a phase diagram

TL;DR

This study investigates the aging and phase behavior of Laponite suspensions, revealing multiple non-ergodic states, including a newly identified state at high salt concentrations, and proposes a comprehensive phase diagram considering ionic effects.

Contribution

The paper introduces a new phase diagram for Laponite suspensions that accounts for multiple non-ergodic states and the significant role of counterions in aging dynamics.

Findings

Identification of two distinct non-ergodic states in Laponite suspensions.

Discovery of a third non-ergodic state at high salt concentrations.

Counterions significantly influence the ionic strength and aging behavior.

Abstract

We study the time evolution of different Laponite suspensions from a low-viscosity ergodic state to a viscoelastic non-ergodic state over a wide range of volume fractions and salt contents. We find that the evolution of non-ergodicity parameter (Debye-Waller factor) splits into two branches for all the samples, which correspond to two distinct dynamically arrested states. At moderately high salt concentrations, on the other hand, a third and new nonergodic state appears that are different from the above two nonergodic states. Measurement of the conductivity of Laponite solutions in pure water shows that the contribution of counterions in the ionic strength is considerable and their role should be taken into account in interpretations of aging dynamics and the phase diagram. Based on these data and available data in the literature, we propose a new (non-equilibrium) phase diagram for Laponite suspensions.