One of the most intriguing phenomena for fluids confined to mesoporous solids is the observation of hysteretic phase transitions. Their development is generally associated with the occurrence of metastable states. In materials with random pore structures, the structural disorder may give rise to very rugged landscapes in the free energy. Depending on the experimental conditions, the system can slowly scramble towards the global equilibrium state. Notably, relaxation dynamics in this regime is barely addressed. By combining different techniques of NMR, we are  able to study macroscopic dynamics accompanying very different phase transitions. In particular, we have shown that, for gas-liquid transitions in disordered mesoporous solids, relaxation dynamics in the hysteresis regime for longer times is dominated by activated barrier crossings between local free energy minima. This is found to be an intrinsically slower process than the relaxation through mass transfer by diffusion which dominates outside the hysteresis regime. Similar observations have been made for liquid-solid transitions occurring in mesoporous solids.

1. R Valiullin, S Naumov, P Galvosas, J Kärger, H J Woo, F Porcheron and P A Monson. Exploration of molecular dynamics during transient sorption of fluids in mesoporous materials. Nature 443:965-968, 2006. BibTeX

@article{2006,
author = "Valiullin, R. and Naumov, S. and Galvosas, P. and Kärger, J. and Woo, H. J. and Porcheron, F. and Monson, P. A.",
title = "Exploration of molecular dynamics during transient sorption of fluids in mesoporous materials",
journal = "Nature",
volume = 443,
pages = "965-968",
year = 2006
}

2. S Naumov, R Valiullin, P A Monson and J Kärger. Probing memory effects in confined fluids via diffusion measurements. Langmuir 24:6429-6432, 2008. BibTeX

@article{2008,
author = "Naumov, S. and Valiullin, R. and Monson, P. A. and Kärger, J.",
title = "Probing memory effects in confined fluids via diffusion measurements",
journal = "Langmuir",
volume = 24,
pages = "6429-6432",
year = 2008
}

3. D Kondrashova, C Reichenbach and R Valiullin. Probing pore connectivity in random porous materials by scanning freezing and melting experiments. Langmuir 26:6380-6385, 2010. BibTeX

@article{2010,
author = "Kondrashova, D. and Reichenbach, C. and Valiullin, R.",
title = "Probing pore connectivity in random porous materials by scanning freezing and melting experiments",
journal = "Langmuir",
volume = 26,
pages = "6380-6385",
year = 2010
}