(326c) Oscillatory Structural Forces Between Drops and Bubbles

In complex fluids, soft or deformable components, such as drops, bubbles, or capsules, respond to their surrounds in a far more complicated manner than rigid particle dispersions. This creates challenges in the processing and the characterization of these systems for a diverse set of applications. These applications range from the purification of minerals or pharmaceuticals using solvent extraction processes, to the formulation of emulsions and foams in food and personal care products. Through a combination of novel experimental methods, mainly using Atomic Force Microscopy (AFM) to visualize the collisions between micro-drops or micro-bubbles on the nanoscale, coupled with theoretical models, we have been able to quantitatively link the dynamic coupling of shape changes with external forces that control their behavior for a range of systems involving drops and bubbles. 

This talk will focus on how oil-water and air-water deformable interfaces are mediated by the presence of highly concentrated surfactant systems or non-adsorbing poly-electrolytes. We observe significant differences between the structural forces between these deformable interfaces compared to the periodic oscillatory structural forces commonly observed between rigid interfaces. In addition, quantitative comparison between these system types indicates that the deformable nature of droplets allows them to act as far more sensitive probes than solid spheres. Furthermore, the responsive nature of soft surfaces can give rise to unexpected behavior not encountered in rigid systems including reversible aggregation/flocculation for emulsion droplets and, potentially, spatial ordering within concentrated emulsion phases.  The impact of hydrodynamic drainage effects on the resulting force behavior as well as changes associated with the aspect ratio of the nano-colloid will also be discussed.