Effect of surface interactions on the hysteresis of capillary condensation in nanoporesF. Casanova1, C. E. Chiang1, C.-P. Li1, I. V. Roshchin1, 2, A. M. Ruminski3, M. J. Sailor3 and I. K. Schuller1
1 Physics Department, University of California - San Diego, La Jolla, CA 92093, USA
2 Physics Department, Texas A&M University - College Station, TX 77843, USA
3 Department of Chemistry and Biochemistry, University of California - San Diego, La Jolla, CA 92093, USA
received 18 September 2007; accepted in final form 12 November 2007; published January 2008
published online 7 December 2007
Gas adsorption and liquid desorption of a number of organic vapors in anodized nanoporous alumina, with controlled geometry (cylindrical pore diameters from 10 to 60 nm), are studied using optical interferometry. The narrow-diameter distribution of disconnected pores allows checking the validity of the (long-predicted but not experimentally verified) Kelvin equation without any adjustable parameters, modeling or other assumptions. Evaporation occurs at liquid-vapor equilibrium according to this equation, whereas condensation occurs from metastable states of the vapor phase by nucleation, enhanced by surface defects inside the nanopores. This produces hysteresis, in qualitative agreement with theoretical models and simulations that use Van der Waals interactions between the fluid and the pore surface. The reproducibility of the hysteresis depends on the strength of these interactions, which play an important role in the dynamics of capillary condensation.
64.70.Fx - Liquid-vapor transitions.
81.07.-b - Nanoscale materials and structures: fabrication and characterization.
05.70.Np - Interface and surface thermodynamics.
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