Science / Technology - Colloquium
Monday, September 18, 2006
4:00 PM-5:00 PM
Olin Hall
107
This talk presents a study on the structure and the dynamics of a nano-colloidal silica gel dispersed in an organic solvent (octylcyanobiphenyl, 8CB) as a function of silica density by x-ray intensity fluctuation spectroscopy (XIFS). The silica density of the dispersed aerosil gel samples ranged from 0.03 to 0.20 g cm-3 and the autocorrelation of the silica scattering were probed over the q range from 0.03 to 0.15 nm-1 (corresponding to length scales from 42 to 209 nm) at a constant room temperature at which 8CB is in the smectic-A phase. The gel structure has a fractal dimension in this density range of df ~ 2.15. The time autocorrelation functions of the gels show clear density-dependent and complex dynamics. The gel relaxation times are very long and become bimodal with nonergodic character for densities from 0.10 to 0.16 g cm-3. In this same density range, the fluctuation contrast (strength) is a minimum while the relaxation time becomes independent of wavevector. Together, these results indicate that there is a narrow silica density range for these gels in which the dynamics changes dramatically. This suggests a complex phase diagram for the dynamics of aerosil gels as a function of densification.
Cost: FREE
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Suggested Audiences: College
E-mail:
snj@wpi.edu
Phone: 508-831-5392
Last Modified: September 15, 2006 at 10:31 AM
Powered by the Social Web - Bringing people together through Events, Places, & Common Interests