Dynamic light scattering study of nonexponential relaxation in supercooled 2Ca(NO3)2_ʀ3KNO3
Sidebottom, David L.
Sorensen, C. M.
We have performed depolarized dynamic light scattering (photon correlation) measurements on the ionic glass forming mixture 2Ca(NO3)2⋅3KNO3 above its glass transition in the temperature range 68–86 °C. We find the relaxation function is a stretched exponential. The average relaxation time follows an Arrhenius temperature dependence and can be related to motions on a molecular scale. The width parameter β does not vary with temperature and is β=0.40±0.05. Combination of our β data with other literature values shows that β evolves with temperature over a larger range. At high temperature, β crosses over from β=1 to β<1 at a temperature which matches well with where the viscosity first deviates from a power law behavior. β then evolves downward with lowering temperature and then settles at 0.4 roughly 30 °C above the glass transition Tg. This behavior corresponds well with recent theory relating the glass transition to the ramification of phase space but it implies that the percolation of phase space occurs well above Tg.
Sidebottom, D. L. & Sorensen, C. M. (1989). Dynamic light scattering study of nonexponential relaxation in supercooled 2Ca(NO3)2_ʀ3KNO3. Jouranl of Chemical Physics, 91, 7153-7158
American Institute of Physics