Interaction of surfaces modified with polymers or surfactants. . . . . . . . . . . . . . . . . . . . . . . . . . . . The wetting and adhesion properties of solid surfaces, the "attitude" of fibres towards the deposition of solid particles, and the stability of dispersion particles against aggregation can all be modified by adsorbing polymers or surfactant molecules. The resulting change in surface forces can be rather subtle, but still make all the difference for the observable macroscopic behavior. We use the Femto-Newton resolution of Total Internal Reflection Microscopy (TIRM) to study the effect of polymer coatings and adsorbed surfactant layers on the interaction between a colloidal probe particle and a flat substrate. Holding our probe particle in an optical trap between consecutive experiments allows us to measure forces between the same particle and substrate area before and after adsorption of a polymer layer, and again after exchanging the surrounding medium. This way we can isolate the effect of polymer adsorption and of the polymer's response to changes in solution parameters such as pH, temperature, or salt concentration.

Electrostatic interaction between colloidal surfaces in aqueous solutions . . . . . . . . . . . . . . . . . . . In the common situation where surface charge arises from the reversible adsorption of mobile ions or from the dissociation of weekly acidic or weekly basic surface groups, the equilibrium charge density of two interacting surfaces is a function of their separation. We study this adjustment of surface charge and electrostatic surface potential to the surface separation, known as "charge regulation", both experimentally, via interaction measurements, and theoretically, within the framework of Poisson-Bolzmann (mean field) theory.

Electrostatic Interaction in non-polar liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... should not be very important, according to conventional wisdom, because the energetic cost of generating or maintaining electric charges in nonpolar media is simply too high, and thus electric charges should not exist in these environments. Many observations of strong electrostatic effects in nonpolar oils, however, tell a different story. We now understand that large ions from organic salts and reversed surfactant micelles provide a way to overcome the usual limitations. Exactly how that works, and how we can use electrostatics in oily media for directed self-assembly and the development of new materials, we are currently investigating...

The packing and interaction of solid particles in liquid-liquid interfaces . . . . . . . . . . . . . . . . . . . . ... is something we try to understand and control because of interesting applications involving specialty filter membranes, particle-stabilized emulsions or the encapsulation of emulsion droplets containing drugs or other active ingredients. From a theoretical standpoint, the interaction of particles in liquid interfaces is extremely complex because it typically involves different types of forces, including charge multipole interaction across two different media and capillary forces introducing many-body effects. We focus on experimental studies of particles in macroscopic oil-water interfaces and on emulsion droplets. In particular we try to understand the effect of salt and added surfactant in these systems.

Double emulsions and polymer capsules made from double emulsions . . . . . . . . . . . . . . . . . . We study double emulsions made either by batch emulsification or, in a droplet-by-droplet fashion, using microfluidic capillaries. By introducing a variety of interesting polymers and particles and extracting the middle phase of our double emulsions, we explore new designs for polymer capsules that may serve as vehicles for controlled drug delivery...

©2008 Georgia Institute of Technology :: Atlanta, GA 30332
Designer: William Garrity