Alexey Khokhlov

Freezing of fluids in disordered mesopores

Freezing and melting behaviors of a fluid confined to pores of mesoporous silicon with a modulated structure have been studied using NMR techniques. The molecular self-diffusivities, measured along the freezing and melting transitions, unveiled essential differences in the configuration of the frozen domains. This suggests that freezing is dominated by a pore-blocking mechanism. Freezing kinetics is found to exhibit very slow long-time dynamics, following a ln(2)(t) dependence. This type of time dependence may result if the front of the frozen phase is assumed to propagate in the random potential field created by the disorder of the porous silicon channels, similar to the mechanism of Sinai diffusion. The free energy barriers calculated from the kinetic measurements and estimated using a thermodynamical model yield a consistent picture of the freezing process in the presence of quenched disorder.

Characterization of Pore Size Distribution in Porous Silicon by NMR Cryoporosimetry and Adsorption Methods

The results of studying the pore size distribution of mesoporous silicon by NMR cryoporosimetry are described. These data are compared with the results obtained by adsorption methods.

Estimation of Pore Sizes in Porous Silicon by Scanning Electron Microscopy and NMR Cryoporometry

Certain possibilities of scanning electron microscopy and cryoporometry based on nuclear magnetic resonance (NMR) have been evaluated to determine pore sizes in porous silicon. The results obtained by these methods have been compared. NMR cryoporometry has been shown to be promising in the investigation of porous materials.