Gelation and anomalous viscosity dynamics in aqueous dispersions of synthetic hectorite

Abstract

Exfoliated clay nanosheets (CNSs) of synthetic hectorite (s-hectorite) have been used for synthesizing advanced functional materials and gels that exhibit high transparency, high mechanical toughness, and many unprecedented characteristics like optical anisotropy, cell harvesting, instant strong adhesion, and self-healing. Therefore, it is important to determine the rheological properties of aqueous s-hectorite dispersions in terms of the CNS microstructures formed in the dispersion. Herein, viscosity changes in aqueous dispersions of s-hectorite were determined using a vibration viscometer to measure viscosity under agitated and static conditions. Upon varying the pH and salt concentration, aqueous dispersions of s-hectorite exhibited a maximum viscosity accompanied by gelation. Additionally, the aqueous dispersion with maximum viscosity exhibited large and complex time-dependent viscosity changes in the static state after cessation of stirring. The anomalous viscosity dynamics depended on the types of clay, acid (salt), temperature, repetitions, and agitation conditions used. The mechanisms for viscosity dynamics have been discussed in terms of variations in the CNS microstructures. It is inferred that anomalous viscosity dynamics are a general phenomenon in multicomponent dispersion systems containing CNSs.