Influence of particle composition and thermal cycling on bijel formation

Abstract

Colloidal particles with appropriate wetting properties can become very strongly trappedat an interface between two immiscible fluids. We have harnessed this phenomenon tocreate 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 acolloid-stabilized emulsion with fluid-bicontinuous domains. The potential to create thesegels was first predicted using computer simulations. Experimentally we use mixtures ofwater and 2,6-lutidine at the composition for which the system undergoes a criticaldemixing transition on warming. Colloidal silica, with appropriate surface chemistry, isdispersed while the system is in the single-fluid phase; the composite sample is then slowlywarmed well beyond the critical temperature. The liquids phase separate via spinodaldecomposition and the particles become swept up on the newly created interfaces. As thedomains coarsen the interfacial area decreases and the particles eventually becomejammed together. The resulting structures have a significant yield stress and arestable for many months. Here we begin to explore the complex wetting propertiesof fluorescently tagged silica surfaces in water–lutidine mixtures, showing howthey can be tuned to allow bijel creation. Additionally we demonstrate how theparticle properties change with time while they are immersed in the solvents.