Braun Group People
Dr. Mark Losego
Post Doctoral Researcher
Ph.D. in Materials Science and Engineering, North Carolina State University (2008)
M.S. in Materials Science and Engineering, North Carolina State University (2005)
B.S. in Materials Science and Engineering, Penn State University (2003)
Structure-Property Relations in Colloidal Glasses and Gels
This project aims to expand upon the current understanding of the structure-property relationships in colloidal glasses and gels. Sterically stabilized colloidal particles behave as ideal hard sphere systems. It is well known that such systems undergo a glass transition at a particle volume fraction of 0.58 in an index-matched solvent. Similar gel transitions can be induced at lower particle volume fractions by introducing a non-interacting short chain polymer, which drives a “depletion attraction” between the particles (a consequence of osmotic pressure).
Studies of the rheological properties as a function of particle volume fraction (or polymer concentration) reveal abrupt increases in viscosity around the glass (or gel) transition. These properties have been correlated to a state of short-range order in colloidal packing, as determined with light and neutron scattering. While such scattering experiments reveal no further structural changes beyond the glass/gel transition, solution viscosity continues to increase. This project focuses on using novel characterization techniques to probe the finer scale structural changes that cause this continued change in rheological behavior.
Below is a scanning electron microscope image of polymethylmethacrylate (PMMA) particles stabilized with a poly(12-hydroxystearic acid)-g-PMMA comb polymer which serves as a model hard sphere system for these studies. The histogram in the upper left corner gives the particle size distribution and confirms a polydispersity below 3%.
Professor Paul Braun • Phone: +1.217.244.7293 • Fax: +1.217.333.2736 • Email: pbraun@illinois.edu
Department of Materials Science and Engineering • University of Illinois at Urbana-Champaign