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DY: Fachverband Dynamik und Statistische Physik

DY 21: Finite size effects at phase transitions II (session accompanying the symposium of the same name)

DY 21.6: Talk

Wednesday, March 28, 2007, 15:15–15:30, H3

Phase transitions of fluids in mesopores assessed by NMR — •Rustem Valiullin and Jörg Kärger — Department of Interface Physics, University of Leipzig, Germany

The adsorption hysteresis phenomenon is a classical example of a mesoscalic confinement effect upon macroscopical properties of fluids. It is suggested that the history-dependent character of the adsorbate accommodation in random nanoporous structures may result from a rugged free energy landscape with many local minima separated by free energy barriers. As it was inferred from computer simulation studies [1], activated crossing of these barriers leads to an extremely slow relaxation to the equilibrium state. In the present work, these predictions have been addressed experimentally using NMR methods. Based on a self-consistent set of experimental data provided by NMR, namely on adsorption kinetics and local self-diffusivities, the anomalously slow intra-pore density relaxation in mesoporous glasses with random porous structure has been proved in the hysteresis region [2]. At the same time, in the out-of-hysteresis region, as expected, the density relaxation has been measured to be diffusive. The observed slowing down of the density relaxation is discussed in the frame of a random field Ising model [3], which has been successfully used to describe critical phenomena of binary liquids in random glasses.

[1] H. J. Woo and P. A. Monson, Phys. Rev. E 67, 041207 (2003).

[2] R. Valiullin et al., Nature 443, 965 (2006).

[3] D. A. Huse, Phys. Rev. B 36, 5383 (1987).