W0235

Complex Mechanical Modulus and Structure of Hydrogels. E. Guilbert and J. Kieffer, Department of Materials Science and Engineering, J.D. Bass, Department of Geology, University of Illinois, Urbana, IL 61801 USA

The Brillouin light scattering technique has been used to determine the complex mechanical modulus of optically transparent hydrogels, in the GHz-frequency regime.  These measurements allow one to investigate structural dynamics on a molecular scale. The storage component of the modulus reflects the structural integrity and connectivity in the gel backbone, whereas the loss component provides a measure for the energy dissipated upon aperiodic motions of small structural moieties. These measurements can therefore be used to monitor the structural assembly during condensation of gels, as well as to determine the viscous friction between backbone and pore fluid. The latter phenomenon is responsible for the cracking of gels upon drying.

To calibrate the information resulting from Brillouin scattering in terms of the pore size and shape, we carried out complementary structural characterization of the gels using small-angle x-ray scattering and BET adsorption porosimetry. In this study, the gel structure was systematically modified by means of the initial chemical composition and the aging treatment. Discussion of the results will focus on identifying accelerated, failure-free, drying schedules for gels.