Physics Colloquium - Thursday, Feb. 12th, 2009, 4:00 P.M.

Jaci Conrad
University of Illinois, Urbana

Colloidal suspensions are ubiquitous in industrial and technological applications, and moreover serve as excellent model systems for a variety of complex fluids. In particular, the structure and flow properties of non-equilibrium suspensions are relevant for materials such as inks, coatings, paints, and personal care products. In this seminar I will discuss three studies relating the structure of non-equilibrium colloidal suspensions to their flow properties. First, we use confocal microscopy to investigate relationships between structure and dynamics near the hard-sphere colloidal glass transition, one of the fundamental unsolved problems in condensed matter physics. By identifying slowly-relaxing regions within our samples, we show that the structure of these clusters is correlated to the macroscopic mechanical properties of the suspension. Second, we use microscopy, light scattering, and rheology to characterize the properties of dense colloidal gels formed via arrested phase separation. These dense gels exhibit structural properties of both fractal colloidal gels and colloidal glasses, yet their mechanical properties are strikingly different from either. Finally, we design model colloidal gels to mimic inks used for direct ink writing, a rapid prototyping techniques, and use microscopy to investigate their flow properties in microchannels. Both the extent of flow-induced structural disruption in the colloidal gel and the qualitative features of its flow profile are directly related to its bulk mechanical properties. Collectively, these measurements yield fundamental insight into the relationship between structure and dynamics in non-equilibrium colloidal suspensions, and provide guidance towards the design of improved materials for extrusion.