Nano-scale Forces between Drops and Bubbles in Soft Complex Fluids
11/5/2012, 3:10 pm - 4:00 pm
Raymond R. Dagastine
Department of Chemical and Biomolecular Engineering and the Particulate Fluids Processing Centre, The University of Melbourne, Victoria, Australia
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 relevant to applications as diverse as the purification of minerals or pharmaceuticals using solvent extraction processes to the formulation of emulsions and foams in food and personal care products. Our research group has developed novel methods to characterize the underlying nanoscale interactions between the colloidal size deformable objects that govern the behavior of soft complex fluids in these applications. Through a combination of novel experimental methods and 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.
Our approach has focused on studies that are highly fundamental in nature in parallel with studies on more applied systems, often with the hope of translating knowledge from the fundamental systems to more applied areas. Our experimental approach has employed innovative methods using mainly Atomic Force Microscopy (AFM) to visualize the collisions between micro-drops(1) or micro-bubbles (2-3) on the nanoscale. This is coupled with a companion theoretical analysis to account for interfacial deformation, surface chemistry and fluid flow between the drops or bubbles to quantitatively describe the measurements on the scale from microns to nanometers.
This talk will first highlight some key fundamental findings including the coalescence behavior of pristine oil drops and bubbles as a function of pH and gas type. Then by increasing the collision speed using linear, non-linear or cyclical collision velocities we will demonstrate counter-intuitive coalescence behavior between micro-bubbles or micro-drops due to hydrodynamic coupling with implications in areas such as micro-fluidics. The talk will then focus on snapshots of systems with more complex or applied natures including emulsion stability in highly concentrated nano-colloid fluids (e.g. micelles, nanoparticles, micro-emulsions) and the interfacial material properties of clay stabilized emulsions. The above examples showcase the utility of these methods to help bring new understanding to both fundamental and complex systems affecting macroscopic drop and bubble behavior.
Monday, November 5, 2012
3:10 p.m. - 4:00 p.m.
5326 Stevenson Center
Reception at 2:45 p.m.