Experimental Evidence for the Pore Size Dependence of Elastic Properties in a Liquid Adsorbate Confined to Nanopores.

The elasticity of adsorbates is relevant for many applications of porous materials. Theoretical studies predict a pronounced increase of elastic moduli for adsorbates under nanoconfinement, but an experimental confirmation is still missing. Here we present an ultrasonic study on the longitudinal modulus βAr,ads of liquid argon in porous glass samples with different pore radii between 1.8 and 12.8 nm. The analysis of the measured moduli of empty, β0, and filled samples, β, reveals that the modulus of the adsorbate, βAr,ads, increases linearly with the inverse pore radius, 1/rP, as predicted by theory.