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Dynamics of specific heat and other relaxation processes in supercooled liquids by impulsive stimulated scattering

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Laser based impulsive stimulated scattering or transient grating excitation in a heterodyne diffraction scheme is a powerful method to extract information about different relaxing properties from different signal contributions. Longitudinal acoustic waves are detected simultaneously with thermal expansion and thermal diffusion. Careful fitting of the time-domain density response at different temperatures makes it possible to obtain the various relaxing physical parameters, and to construct Arrhenius plots for the respective relaxation processes. In this work we focus on the influence of the specific heat capacity C on the slower part of the density response function S(t), and, inversely, on the possibility to extract from experimental S(t) data the relaxation behaviour C(omega). The specific heat capacity is relevant for both the initially rising part of the impulsive stimulated scattering signal (together with the time and frequency dependent thermal expansion eta(t)), and for the thermal diffusion dominated decrease of the signal at later times after the excitation. By simulating S(t) data in different scenarios, we address the feasibility of unravelling the impulse response functions C(t) and eta(t) (and via Fourier transform also C(omega) and eta(omega)) by careful fitting of the signal. This approach offers a unique possibility to extend the 100 kHz bandwidth of current dynamic calorimetric techniques determining C(omega) (photopyroelectric spectroscopy) to the sub-GHz range.
Tijdschrift: 3RD INTERNATIONAL SYMPOSIUM ON LASER ULTRASONICS AND ADVANCED SENSING
ISSN: 1742-6588
Issue: 1
Volume: 278
Pagina's: 012021
Toegankelijkheid:Closed