Elasticity and phase behaviour of n-heptane and n-nonane in nanopores
FR 7.2 Experimentalphysik, Universität des Saarlandes - 66123 Saarbrücken, Germany
Received: 30 July 2015
Accepted: 26 August 2015
Here we present an ultrasonic study on the elasticity of normal alkanes (n-heptane and n-nonane) in the nanopores of porous Vycor glass (average pore radius ). Above the melting temperature we have found a non-zero shear modulus for both n-heptane and n-nonane, which is also typical for the rotator phases of bulk alkanes at temperatures below the melting temperature. This points to the formation of a special molecular order of the adsorbed alkanes. Furthermore, the alkanes undergo a continuous stiffening over a broad temperature range (of for heptane or for nonane). The results clearly indicate that nanoconfinement induces an extremely broad continuous transition of heptane and nonane into a crystalline low-temperature phase.
PACS: 64.70.Nd – Structural transitions in nanoscale materials / 62.25.-g – Mechanical properties of nanoscale systems / 68.43.-h – Chemisorption/physisorption: adsorbates on surfaces
© EPLA, 2015