Robert W. Vaughan Lecture in Chemical Engineering

Microfluidic techniques enable exquisite control over the physical and chemical properties of experimental systems.  We will describe techniques we have developed to sculpt chemical environments in space and time, and interferometric methods to visualize these concentration fields as they evolve.  We will illustrate with direct, dynamic measurements of water sorping into ionic liquids, reagent depletion during interfacial polymerization reactions, and solvent diffusion through hydrogels.

We then use this solution-sculpting to study the diffusiophoretic migration of colloids under imposed chemical gradients.  Such phenomena occur quite generally in response to non-equilibrium chemical fluxes, and therefore arise in a wide variety of real-world systems.  Nonetheless, diffusiophoresis has remained stubbornly difficult to observe or characterize directly.  We will discuss the physico-chemical phenomena that underlie diffusiophoresis, and therefore how to intuitively design systems with desired diffusiophoretic properties. 

Finally, we will build on this foundation to introduce conceptually new colloidal interactions that are non-equilibrium but long-lived, much longer-ranged than is possible in aqueous suspensions, and are chemically-specific.  We envision a broad role for such interactions in destabilizing suspensions, breaking emulsions, and extracting compounds.