科研之友
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摘要
We report a comparative neutron scattering study of the molecular mobility and nonexponential relaxation of three structurally similar glass-forming liquids, isopropanol, propylene glycol, and glycerol, both in bulk and confined in porous Vycor glass. Confinement reduces molecular mobility in all three liquids, and suppresses crystallization in isopropanol. High-resolution quasielastic neutron scattering spectra were fit to Fourier transformed Kohlrausch functions exp[-(t/tau)(beta)], describing the alpha-relaxation processes in these liquids. The stretching parameter beta is roughly constant with wavevector Q and over the temperature range explored in bulk glycerol and propylene glycol, but varies both with Q and temperature in confinement. Average relaxation times <tau(Q)> are longer at lower temperatures and in confinement. They obey a power law <tau(Q)> proportional to Q(-gamma), where the exponent gamma is modified by confinement. Comparison of the bulk and confined liquids lends support to the idea that structural and/or dynamical heterogeneity underlies the nonexponential relaxation of glass formers, as widely hypothesized in the literature.
- 出版日期2011-3-21
