Acoustic, thermal and flow processes in a water filled nanoporous glasses by time-resolved optical spectroscopy

We present heterodyne detected transient grating measurements on water filled Vycor 7930 in the range of temperature 20 - 90 degrees C. This experimental investigation enables to measure the acoustic propagation, the average density variation due the liquid flow and the thermal diffusion in this water filled nano-porous material. The data have been analyzed with the model of Pecker and Deresiewicz which is an extension of Biot model to account for the thermal effects. In the whole temperature range the data are qualitatively described by this hydrodynamic model that enables a meaningful insight of the different dynamic phenomena. The data analysis proves that the signal in the intermediate and long time-scale can be mainly addressed to the water dynamics inside the pores. We proved the existence of a peculiar interplay between the mass and the heat transport that produces a flow and back-flow process inside the nano-pores. During this process the solid and liquid dynamics have opposite phase as predicted by the Biot theory for the slow diffusive wave. Nevertheless, our experimental results confirm that transport of elastic energy (i.e. acoustic propagation), heat (i.e. thermal diffusion) and mass (i.e. liquid flow) in a liquid filled porous glass can be described according to hydrodynamic laws in spite of nanometric dimension of the pores. The data fitting, based on the hydrodynamic model, enables the extraction of several parameters of the water-Vycor system, even if some discrepancies appear when they are compared with values reported in the literature.Comment: 32 pages, 11 figure

Translation-Rotation Coupling in Transient Grating Experiments : Theoretical and Experimental Evidences

The results of a Transient Grating experiment in a supercooled molecular liquid of anisotropic molecules and its theoretical interpretation are presented. These results show the existence of two distinct dynamical contributions in the response function of this experiment, density and orientation dynamics. These dynamics can be experimentally disentangled by varying the polarisation of the probe and diffracted beams and they have been identified and measured in a Heterodyne Detected experiment performed on m-toluidine. The results of the theory show a good qualitative agreement with the measurements at all temperatures.Comment: PDF format, 14 pages including 4 figures, accepted for publication in EPL. minor modification

Analysis of a heterodyne-detected transient-grating experiment on a molecular supercooled liquid. II. Application to m-toluidine

International audienceThis paper reports the first detailed analysis of a transient grating TG experiment on a supercooled molecular liquid, m-toluidine, from 330 K 1.75Tg to 190 K 1.01Tg based on the theoretical model presented in Paper I of this series. This method allows one to give a precise description, over a wide dynamical range, of the different physical phenomena giving rise to the signals. Disentangling the isotropic and the anisotropic parts of the TG response, a careful fitting analysis yields detailed information on the rotation-translation coupling function. We also extract the structural relaxation times related to the "longitudinal" viscosity over almost 10 decades in time and the corresponding stretching coefficient. The value of some other parameters and information on their thermal behavior is also reporte

Acoustic and relaxation processes in supercooled o-ter-phenyl by optical-heterodyne transient grating experiment

The dynamics of the fragile glass-forming o-ter-phenyl is investigated by time-resolved transient grating experiment with an heterodyne detection technique in a wide temperature range. We investigated the dynamics processes of this glass-former over more then 6 decades in time with an excellent signal/noise. Acoustic, structural and thermal relaxations have been clearly identify and measured in a time-frequency window not covered by previous spectroscopic investigations. A detailed comparison with the density response function, calculated on the basis of generalized hydrodynamics model, has been worked out