Dr. Marjorie Longo
Department of Chemical Engineering, College of Engineering
University of California, Davis
Mechanical and Adhesive Properties of Crude Oil Droplets: Contributions of Interfacial Components
Dr. Marjorie L. Longo, who is a professor at the University of California, Davis in the Department of Chemical Engineering, received her undergraduate and Ph.D. degrees at the University of California, Santa Barbara. Her PRF New Direction (ND) grant focuses on the mechanical and adhesive properties of crude oil droplets.
Dr. Longo’s research involves surfactants and lipids. Two familiar examples of these classes of molecules are surfactant hand soaps and biological lipid membranes. The original inspiration for this research was Dr. Longo’s desire to apply the technique of micropipette aspiration to a new area–the properties of thin surfactant films on oil droplets. That led to the exploration of the properties that emerge in the self-assembled thin films and micelles of these molecules when added into other components and interfaces.
According to Dr. Longo, “Very little historical measurements of mechanical properties of surfactant and lipid films exist, partially because most other measurement techniques require large amounts of material and they are not optimum for measuring properties of a nanometer-thin film.” Her PRF-funded research involves measuring the changes in the mechanical properties of charged surfactant thin films as they add salt, oppositely charged surfactants, and interfaces. Dr. Longo’s approach involves “applying force to the surfactant film, by the tip of an atomic force microscope, on a hard surface or, by aspirating with a micropipette, on a soft surface.”
Dr. Longo stated there were a number of surprising results. For example, she found that for self-assembled films on a graphite surface in water “some portion of the film protruded into the water like hairs on a brush.” Additionally, she found that surfactant films were much less viscous when they were assembled onto oil droplets of octane molecules compared to the larger dodecane molecules. Dr. Longo hypothesized that this is because “the oil is influencing how ordered the film is.” Another finding was that the highest viscosities were obtained in films containing negatively and positively charged surfactants, which attract each other, and seem to form tightly-packed films.
Dr. Longo explains these research findings will help better understand “the tendency for oil droplets to coalesce by relating this to the mechanical properties of the surfactant film.” She feels that, “by our mechanical properties measurements, we have already contributed to understanding the process of coalescence.” The process of coalescence is important in many fields such as food, petroleum, and biotechnology. In the future, Dr. Longo would like to “characterize the coalescence of surfactant-coated oil droplets and relate the tendency for oil droplets to coalesce to the mechanical properties of the surfactant film.”
The PRF grant gave Dr. Longo the opportunity to assemble a research team, explore a new research area, and to involve undergraduate and graduate students in her research. In order to perform the research, she explains that, “we needed to revive our micropipette aspiration equipment, and I am grateful for PRF support to purchase the lab supplies necessary to achieve this.”