(742b) Interfacial Routes to Colloidal Gelation

Colloidal gels are percolating particle networks with arrested dynamics and remarkable rheology, typically stemming from attractive interparticle interactions.  These properties have been scientifically investigated and exploited in a variety of technological applications including food processing, cosmetics, oil industries, and direct-write assembly.  In this talk, two new routes to colloidal gelation will be discussed, which exploit colloidal self-assembly at liquid-liquid interfaces. The first system contains a two-phase liquid mixture with particles that have a three-phase contact angle θ > 90°.  The obtuse contact angle leads to bridging of dispersed droplets by a monolayer of interfacial particles, and gelation results from a percolating three-dimensional particle/droplet network.  The second system involves a suspension of neutrally wetting colloidal particles in a binary liquid mixture undergoing spinodal decomposition.  Here, particles are swept up by the newly formed interface upon phase separation and become jammed when the interfacial area just accommodates all the particles. Gelation then results from two-dimensional particle jamming at the interface of a three-dimensional bicontinuous structure.  Using quantitative confocal microscopy and bulk rheometry, the microstructural origins of gel-like rheology in these systems are examined and compared to more traditional colloidal gels in which attractive interparticle interactions are required for gelation. Finally, promising applications of these novel materials in a variety of technological areas will be discussed.