Matthew Douglas Reichert

Interfacial Tension Dynamics, Interfacial Mechanics, and Response to Rapid Dilution of Bulk Surfactant of a Model Oil–Water-Dispersant System

In the 2010 Deepwater Horizon rig explosion and subsequent oil spill, five million barrels of oil were released into the Gulf over the course of several months. Part of the resulting emergency response was the unprecedented use of nearly two million gallons of surfactant dispersant at both the sea surface and well head, giving rise to previously untested conditions of high temperature gradients, high pressures, and flow conditions. To better understand the complex interfacial transport mechanisms that this dispersant poses, we develop a model surfactant-oil-aqueous system of Tween 80 (a primary component in the Corexit dispersant used in the Gulf), squalane, and both simulated seawater as well as deionized water. We measure surfactant adsorption dynamics to the oil-aqueous interface for a range of surfactant concentrations. Using techniques developed in our laboratory, we investigate the impact of convection, step changes in bulk concentration, and interfacial mechanics. We observe dynamic interfacial behavior that is consistent with a reorganization of surfactant at the interface. We demonstrate irreversible adsorption behavior of Tween 80 near a critical interfacial tension value, as well as measure the dilatational elasticity of equilibrium and irreversibly adsorbed layers of surfactant on the oil-aqueous interface. We report high values of the surface dilatational elasticity and surface dilatational viscosity, and discuss these results in terms of their impact regarding oil spill response measures.

Coalescence behavior of oil droplets coated in irreversibly-adsorbed surfactant layers.

Coalescence between oil caps with irreversibly adsorbed layers of nonionic surfactant is characterized in deionized water and electrolyte solution. The coalescence is characterized using a modified capillary tensiometer allowing for accurate measurement of the coalescence time. Results suggest two types of coalescence behavior, fast coalescence at low surface coverages that are independent of ionic strength and slow coalescence at high coverage. These slow coalescence events (orders of magnitude slower) are argued to be due to electric double layer forces or more complicated stabilization mechanisms arising from interfacial deformation and surface forces. A simple film drainage model is used in combination with measured values for interfacial properties to quantify the interaction potential between the two interfaces. Since this approach allows the two caps to have the same history, interfacial coverage and curvature, the results offer a tool to better understand a mechanism that is important to emulsion stability.

Nano-Engineering by Optically Directed Self-Assembly

Lack of robust manufacturing capabilities have limited our ability to make tailored materials with useful optical and thermal properties. For example, traditional methods such as spontaneous self-assembly of spheres cannot generate the complex structures required to produce a full bandgap photonic crystals. The goal of this work was to develop and demonstrate novel methods of directed self-assembly of nanomaterials using optical and electric fields. To achieve this aim, our work employed laser tweezers, a technology that enables non-invasive optical manipulation of particles, from glass microspheres to gold nanoparticles. Laser tweezers were used to create ordered materials with either complex crystal structures or using aspherical building blocks.