Influence of the Laplace pressure on the elasticity of argon in nanopores

At the beginning of an isothermal desorption process with the adsorbate argon, the nanopores of the porous glass sample remain virtually completely filled over a certain pressure range. A reduction of the external pressure p below the bulk vapour pressure of argon, p 0 , results, however, in the formation of concave menisci at the pore ends. The related decrease of the radius of curvature causes an increase of the negative Laplace pressure. This occurance is known to provoke a contraction of porous samples. Here we show that the Laplace pressure also influences the elastic properties of the filled porous sample. A decrease of the radius of curvature at the pore ends becomes noticeable in a decrease of the effective longitudinal modulus. The analysis of our ultrasonic measurements reveals that this decrease of the effective longitudinal modulus originates in a reduction of the longitudinal modulus of the adsorbate.