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Fast relaxation in a fragile liquid under pressure

A. Toelle·H. Schober·J. Wuttke·F. Fujara
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Abstract

The incoherent dynamic structure factor of ortho-terphenyl has been measured by neutron time-of-flight and backscattering technique in the pressure range from 0.1 MPa to 240 MPa for temperatures between 301 K and 335 K. Tagged-particle correlations in the compressed liquid decay in two steps. The alpha-relaxation lineshape is independent of pressure, and the relaxation time proportional to viscosity. A kink in the amplitude f_Q(P) reveals the onset of beta relaxation. The beta-relaxation regime can be described by the mode-coupling scaling function; amplitudes and time scales allow a consistent determination of the critical pressure P_c(T). alpha and beta relaxation depend in the same way on the thermodynamic state; close to the mode-coupling cross-over, this dependence can be parametrised by an effective coupling Gamma ~ n*T**{-1/4}.

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A. Toelle, H. Schober, J. Wuttke, F. Fujara. 1998-01-15. Fast relaxation in a fragile liquid under pressure. https://doi.org/10.1103/physrevlett.80.2374

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