Influence of particle composition and thermal cycling on bijel formation

TL;DR

This study investigates how particle composition and thermal cycling influence the formation of bijels, a novel colloid-stabilized bicontinuous gel, highlighting the role of wetting properties and particle aging.

Contribution

It demonstrates how tuning particle wetting properties and understanding particle aging can control bijel formation and stability.

Findings

Wetting properties of silica particles can be tuned for bijel creation

Particle aging affects wetting behavior and bijel stability

Thermal cycling influences the interfacial trapping of particles

Abstract

Colloidal particles with appropriate wetting properties can become very strongly trapped at an interface between two immiscible fluids. We have harnessed this phenomenon to create a new class of soft materials with intriguing and potentially useful characteristics. The material is known as a bijel: bicontinuous interfacially-jammed emulsion gel. It is a colloid-stabilized emulsion with fluid-bicontinuous domains. The potential to create these gels was first predicted using computer simulations. Experimentally we use mixtures of water and 2,6-lutidine at the composition for which the system undergoes a critical demixing transition on warming. Colloidal silica, with appropriate surface chemistry, is dispersed while the system is in the single-fluid phase; the composite sample is then slowly warmed well beyond the critical temperature. The liquids phase separate via spinodal decomposition and the particles become swept up on the newly created interfaces. As the domains coarsen the interfacial area decreases and the particles eventually become jammed together. The resulting structures have a significant yield stress and are stable for many months. Here we begin to explore the complex wetting properties of fluorescently-tagged silica surfaces in water-lutidine mixtures, showing how they can be tuned to allow bijel creation. Additionally we demonstrate how the particle properties change with time while they are immersed in the solvents.