Start
Aug 12, 2010 - 16:00
End
Aug 12, 2010 - 17:30
Venue
Creativity Hall (Room No. 118)
Event Type
Speaker
Dr. Subramanian Ramakrishnan Assistant Professor Department of Chemical and Biomedical Engineering. FAMU-FSU College of Engineering
Title
Connecting Nanoscale Motion and Rheology of Gel-Forming Colloidal Suspensions.
Abstract: A combined x-ray photon correlation spectroscopy and rheometry study is reported of moderately concentrated suspensions of silica colloids that form a gel on cooling. The suspensions are comprised of silica colloids 45 nm in diameter coated with octadecyl-hydrocarbon chains in decalin at colloidal volume fractions ranging from 0.20 to 0.43. During gel formation the suspensions acquire a shear modulus that increases with time while the thermal motion of the colloids becomes localized over an increasingly restricted range. The nanometer-scale localization length characterizing this motion obeys an exact relationship with the shear modulus predicted heoretically from mode coupling calculations (K. S. Schweizer and G. Yatsenko J. Chem. Phys. 127 164505 2007). This scaling thus demonstrates a direct quantitative connection between the microscopic dynamics and macroscopic rheology. It further indicates the importance of local structure over longer-range correlations in dictating the dynamical and mechanical properties of such gels. I will conclude the seminar with a brief overview of research in my group and highlight another project which has been of considerable interest in the last couple of years - in developing a continuous enzymatic process to convert cellulosic biomass to biofuels.About the speaker: S. Ramakrishnan received his BTech (1995) in Chemical Engineering from IIT Chennai M.S. and Ph.D. (2001) from University of Illinois at Urbana-Champaign in the Department of Chemical and Biomolecular Engineering. His focus of research was on studying the structure and rheology of complex fluids with an aim of assembling them into useful structures. This was followed by post doctoral appointments at Princeton University (2001-2002 Chemical Engineering) and at the University of Illinois (2002-2005 Nanoscience Research Centre) before accepting his current job as Assistant Professor of Chemical and Biomedical Engineering at the Florida A&M – Florida State University College of Engineering. Current research interests include rheology of colloidal gels and processing of biomass to biofuels. More information on Ramakrishnan and his interests can be found at www.eng.fsu.edu/~srama.