  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.
