Distinct Enhancement of the Longitudinal Modulus of Liquid Nitrogen in Nanoporous Vycor Glass

Abstract

Nanoconfinement influences various properties of adsorbed substances. The changes of the elastic properties of adsorbates in comparison to those in the bulk state are of great relevance for the development of new nanomaterials as well as in geophysics, but experimental data are limited. The strength of the interaction between adsorbate and pore surface is expected to be a decisive factor for the adsorbate’s elasticity. Here we study the longitudinal modulus βN2,ads of liquid nitrogen confined in the nanopores of Vycor glass using ultrasonic measurements. The analysis of our experimental data in a broad temperature range (63−95 K) reveals a distinct enhancement of βN2,ads in comparison to the longitudinal modulus of bulk nitrogen, βN2,bulk. This strong enhancement by ≈40−70% contrasts to our results for liquid argon for which we observed only a slight enhancement by ≈15%. We attribute this difference between the liquid adsorbates nitrogen and argon to the different interaction strengths between those substances and the OH groups on the pore surface. Furthermore, our measurements indicate a considerably stronger temperature dependence of βN2,ads in comparison to that of βN2,bulk. Our findings indicate that changes of interactions between adsorbate and pore surface can have a significant impact on the adsorbate’s elastic properties.