Effects of colloidal particles on interfacial rheology

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The proposed study focuses on how submicron particles (or "nanoparticles") may accumulate at the oil-water interface and modify its physical properties.  This research is motivated by an industrial process known as "microbial enhanced oil recovery" (MEOR), where bacteria with "appetites" for petroleum are injected into oil wells to help recover residual hydrocarbon.  Much work has been done in the past on the biochemical aspects of this technology.  In contrast, there has been little or no research on the physics of oil-water interfaces that are laden with microorganisms.  In particular, it is important to understand how these surfaces will deform and flow under applied forces.  Instead of working with actual bacteria, we propose to create small inanimate objects that will mimic the microorganisms.  These, for example, can be submicron glass spheres whose surfaces are covered with long chain sugar molecules (polysaccharides).  The "model bacteria" will then be allowed to accumulate at oil-water interfaces (e.g. on the surfaces of submerged oil droplets), and the resulting surface mechanical properties will be quantified.  It is commonly-known that the presence of particles at interfaces can have no effect on their interfacial tensions.  We are, however, concerned with higher-order mechanical properties such as surface viscosities and surface elasticities (collectively known as "rheological properties").  These properties will be quantified using techniques such as the oscillating pendant drop and the micropipette.