Influence of Small Molecule Additives on Gemini Dicarboxylate Lyotropic Liquid Crystal Structure and Stability

In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program of the NSF Chemistry Division, Mahesh Mahanthappa of the University of Wisconsin-Madison is studying how small molecule surfactants, in which a water-soluble headgroup is attached to a water-insoluble tail, self-assemble in water. At high surfactant concentrations in water, these molecules spontaneously form a variety of structurally periodic soft materials known as liquid crystals. Certain liquid crystal structures are particularly useful in practical technical applications, yet these structures are difficult to access and their properties are limited. This project addresses these problems by investigating how adding salts and oils to water/surfactant mixtures enables the formation of these useful liquid crystals. A subset of the resulting materials may find long term application in fields such as therapeutic drug delivery. Another aspect of this project focuses on converting these liquid crystals into useful polymer membranes for energy efficient separations of complex chemical mixtures and for the generation and use of renewable fuels derived from solar energy. The broader impacts of this work include mentoring graduate and undergraduate students in research projects at the boundary between fundamental science and technological innovation, which will is expected to lead to useful materials for future healthcare and renewable energy applications.

This project investigates how small molecule additives control the water concentration-dependent self-assembly of gemini ('twin tail') dicarboxylate surfactants to form lyotropic liquid crystals (LLCs). A special emphasis in this project is placed on identifying methods for stabilizing network phase LLCs with interwoven, periodic, and percolating 3D-networks of aqueous and hydrophobic domains. The influence of various hydrophilic, hydrophobic, and amphiphilic molecular additives on LLC structure formation and stability are being evaluated by polarized light microscopy and temperature-dependent X-ray scattering. These studies are informing the development of mixtures of reactive surfactants and molecular additives that spontaneously form network phase LLCs for subsequent polymerization into functional, nanoporous polymer membranes. Professor Mahanthappa is translating related research results into public outreach demonstrations that showcase the utility of simple 'soaps' in hydraulic fracturing applications ('fracking') for oil and gas recovery, to engage the public in broader discussions of energy harvesting technologies and global energy demands.