$\alpha$-Scale Decoupling of the Mechanical Relaxation and Diverging Shear Wave Propagation Lengthscale in Triphenylphosphite

TL;DR

This study investigates shear acoustic phonons in supercooled triphenylphosphite using impulsive scattering, revealing a decoupling of relaxation and shear wave length scales near a critical temperature, consistent with mode coupling theory.

Contribution

It provides experimental evidence of alpha coupling and decoupling phenomena in supercooled liquids, supporting theoretical predictions of mode coupling theory.

Findings

Evidence of alpha coupling between shear and longitudinal modes up to 231 K

Verification of theoretical exponent for shear wave propagation lengthscale

Identification of a decoupling temperature in supercooled TPP

Abstract

We have performed depolarized Impulsive Stimulated Scattering experiments to observe shear acoustic phonons in supercooled triphenylphosphite (TPP) from $\sim$10 - 500 MHz. These measurements, in tandem with previously performed longitudinal and shear measurements, permit further analyses of the relaxation dynamics of TPP within the framework of the mode coupling theory (MCT). Our results provide evidence of $\alpha$ coupling between the shear and longitudinal degrees of freedom up to a decoupling temperature $T_c$ = 231 K. A lower bound length scale of shear wave propagation in liquids verified the exponent predicted by theory in the vicinity of the decoupling temperature.