The colloidal state is ubiquitous in biology, chemistry, and materials science. It offers a general way to create macroscopically homogeneous combinations of highly dissimilar components, such as milk consisting of immiscible fat and water. Stabilizing the colloidal state in different systems is at the heart of many technological processes. This project is focused on a novel class of colloidal systems. Preliminary studies show that a colloidal state can be realized for different nanoparticles in molten inorganic salt and, probably, in liquid metals. Liquid metals and molten salts are widely used in metallurgy and soldering, as heat transfer fluids in thermal solar technologies, and other important areas. Demonstrating stable colloidal systems in such media and understanding the factors that govern stability may open up opportunities to design new types of composites using a rich toolbox of techniques from colloidal chemistry. A comprehensive education and outreach program accompanies this research and focuses on education enrichment for the underrepresented African-American and Hispanic K-12 populations on Chicago's South Side. This project supports the continued development and distribution of nanoscience educational resources for the U. Chicago chemistry community as well as for K-12 students. This includes the development of a new graduate materials chemistry track at the University of Chicago and a continued successful effort to help undergraduates and high school students gain research experience.
This project is directly relevant to the development of new colloidal systems. Nanoparticles of various transition metals, semiconductors, rare-earth, and magnetic materials form stable colloidal dispersions in various molten salts and liquid metals. The colloidal stability of nanoparticles in these media cannot be explained by traditional stabilization mechanisms. It appears that neither electrostatic nor steric repulsion can explain colloidal stability in a molten ionic salt. Given the very high charge density, electrostatic potential is screened on the sub-nm distance, making electrostatic repulsion short-ranged and inferior compared to van der Waals attraction. The absence of brush-like species at the particle surface in molten salt also rules out the possibility of classical steric stabilization. This project incorporates systematic experimental and theoretical investigations of this class of functional nanomaterials that are colloidally stabilized in molten inorganic salts and liquid metals. Specific aims of this project include the study and development of an understanding of the colloidal stabilization mechanism in molten salts and liquid metals at elevated temperatures, as well as exploration of properties and potential applications for colloidal dispersions of nanomaterials in molten salts and liquid metals.
