INTERNAL SURFACES OF POROUS-MEDIA STUDIED BY NUCLEAR-MAGNETIC-RESONANCE CRYOPOROMETRY

The filling processes of water and cyclohexane in porous silica (with a characteristic pore size of 60 Angstrom) are investigated using the nuclear magnetic resonance (NMR) technique of cryoporometry. In this t echnique, the liquid was frozen in the pores before the temperature wa s raised gradually; melting the smallest particles first and then part icles of increased size. The volume of the molten liquid present was m easured using the height of a T-2 spin echo. The experiments were perf ormed with filling fractions ranging from 10% to 100%. The results sho wed distinctly different behaviors of the fluids, which depended on th e surface adhesion. It was found that water (a fluid which wets the po re surface) forms small puddles-much smaller than the smallest pore si ze-at low filling fractions. These puddles grow in size as more water is added until all the pore volume is filled. Cyclohexane (a non-wetti ng fluid) on the other hand, does not form small puddles but completel y tills the pores with a preference for the smaller pores. Water is fo und to give more accurate results for the pore size distribution than cyclohexane, in 60 Angstrom silica. (C) 1998 American Institute of Phy sics.