Chemical Engineering Seminar Series : Prof. Sachin Velankar.

Capillarity, wetting, and rheology in particulate suspensions. 

A sandcastle owes its stability to capillary forces. Specifically, water bridges induce an attractive interaction between sand grains, which gives the wet sand sufficient yield stress to sustain a sandcastle. Ternary suspensions comprising one particulate species and two immiscible liquids behave similarly, viz. capillary forces induce interparticle attractions, which endow the suspensions with a yield stress. Such suspensions are ideal precursors for new materials, e.g. porous ceramics, 3D printing composite formulations, or conductive plastics. This talk will explore the fundamentals of microstructure development in such ternary suspensions.

We will show that such two-fluid particle suspensions can show a rich diversity of microstructures: particle networks aggregated by fluid menisci, compact capillary aggregates, Pickering emulsions, and bicontinuous morphologies. These microstructures result from a coupling between interfacial tension between the fluids, particle wettability, and viscous forces during mixing. This talk will catalog the transitions between various microstructures, and show how a non-equilibrium morphological map can be constructed for ternary mixtures of particles and two fluids. Clear understanding of such a non-equilibrium state map can guide new approaches for materials development. We will provide examples of flow-processable bicontinuous materials or flow-processable conductive polymer composites, whose development was guided by these insights.

The talk will conclude with a brief discussion of other research in the Velankar group on (1) the large deformation mechanics of polymer materials, and (2) the remarkable phenomenon of polymer hydrate crystallization.