Phase Behavior of Aqueous Suspension of Laponite: New Insights with Microscopic Evidence

TL;DR

This study combines rheological and microscopic analyses to clarify the phase behavior of aqueous Laponite suspensions, demonstrating their gel-like state and providing new insights into their microstructure and gelation dynamics.

Contribution

It provides the first comprehensive microscopic evidence confirming the attractive gel state of Laponite suspensions, resolving longstanding debates in the literature.

Findings

Laponite suspensions exhibit sol-gel transition characteristics across various concentrations.

Fractal dimension depends primarily on Laponite concentration.

Activation energy for gelation decreases with higher Laponite and salt concentrations.

Abstract

Investigating microstructure of suspensions with particles having anisotropic shape that share complex interactions is a challenging task leading to competing claims. This work investigates phase behavior of one such system: aqueous Laponite suspension, which is highly contested in the literature, using rheological and microscopic tools. Remarkably, we observe that over a broad range of Laponite (1.4 to 4 weight %) and salt concentrations (0 to 7 mM), the system overwhelmingly demonstrates all the rheological characteristics of the sol-gel transition leading to a percolated network. Analysis of the rheological response leads to fractal dimension that primarily depends on the Laponite concentration. We also obtain the activation energy for gelation, which is observed to decrease with increase in Laponite as well as salt concentration. Significantly, the cryo-TEM images of the post-gel state clearly show presence of a percolated network formed by inter-particle bonds. The present work therefore conclusively establishes the system to be in an attractive gel state resolving a long-standing debate in the literature.