(589d) Effect of Water Vapor Adsorption on Ultrasonic Wave Propagation in Nanoporous Glasses

Fluids under nanoporous confinement exhibit thermodynamic properties which differ from those observed in bulk. We investigate the effects of nanoconfinement on the compressibility of liquid water by measuring the speed of ultrasonic waves through samples of nanoporous glass during the adsorption and desorption of water vapor. From these experiments, the longitudinal and shear moduli of the water-glass composite are measured as the pores fill and empty. We then apply the Gassmann theory to infer the bulk modulus of the confined water. The results show that confined liquid water exhibits an elevated bulk modulus compared to the bulk value, and is linearly dependent on the Laplace pressure. These results are in qualitative agreement with previous experimental and numerical data reported for non-polar fluids in nanopores, implying that confined fluids are stiffer than bulk fluids irrespective of intermolecular forces. Accurate predictions of fluid-stiffening in nanoporous media may prove relevant for ultrasonic sensing in petrophysics, catalysis, characterization of porous materials, and other applications.