The presence of the surfactants at interfaces reduces the free energy of the interface, and thereby alters the properties of system in regard properties such as wetting, emulsification, or foaming. Control of these properties is crucial in many industries and products. It is particularly challenging to find suitable surfactants in mixed solvent systems (water and a co-solvent such as an alcohol), because the co-solvent reduces the (generalized) hydrophobic phobic repulsion, which in turn reduces the effectiveness of a surfactant. The understanding of what molecular features lead to hydrophobic interactions is rudimentary. While there has been intense research activity in regard to understanding hydrophobic effects associated with protein folding, there has not been as strong an effort to understand hydrophobicity in systems of industrial interest. The proposed research will address the hydrophobic interactions of molecules of industrial relevance, with the aim of better understanding surfactant behavior.
The novelty of this project stems from the investigation of surfactants that have been largely overlooked from a theoretical chemistry perspective, but are nonetheless very important industrially, and from the combined simulation-experiment approach we will use. Note that the simple experiments we propose would not be of such strong enough interest in-and-of-themselves, but when combined with the simulations they will enhance our understanding of the surfactant behavior as well as provide a test of the reliability of the simulations.
Intellectual Merit:
Molecular dynamics simulations will be carried out to elucidate the molecular factors that control surfactant partitioning to surfaces in mixed solvent systems. In addition, surface tension experiments will be carried out on such systems to provide tests of simulation reliability as well as further insights into the surfactant behavior. More specifically, the project will address the following questions: a. Why are silicones so hydrophobic? Despite the importance of silicone surfactants, we are not aware of even one molecular simulation study that addresses why these surfactants are so effective. b. Why do polyethers show unusual variations in hydrophobicity, such that poly(ethylene oxide) is hydrophilic while polyethers with one more or one less CH2 group along the backbone are hydrophobic? c. How do the answers to the above questions change as a co-solvent such as an alcohol is added to water?
Broader Impacts
The project will have a variety of broader impacts: a. Strong efforts to mentor undergraduate researchers. Evidence of our success in this regard is the significant number of undergraduate students who are co-authors on our papers. b. Connections to programs we are developing to educate students with a global perspective in regard to sub-Saharan Africa. These programs are being held both at the University of Botswana and our home institution, Case Western Reserve University. c. The possibility of improved technology arising from a better understanding of the factors that govern surfactant behavior in mixed solvent systems.
