Helium and Hydrogen Adsorbed on Spheres and Cylinders
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We examine the metastable and unstable regimes of condensation of superfluid helium and parahydrogen on spheres and cylinders at finite temperatures, employing finite range density functionals. The goal is to compare calculations of sizes and spreads of films at the onset of metastability and of instability with the predictions of a simple phenomenological model that contemplates the curvature of the substrate. We have focused on two cases, helium on nanospheres and nanocylinders of different materials, and hydrogen on fullerenes. We are able to locate the onset of metastability and of spinodal instability in the adsorption isotherms of every sample and to extract the width of the condensed fluid. It is shown that the predictions of the so-called simple model agree surprisingly well with the more elaborate calculations.
KeywordsCurved substrates Adsorption Instabilities Film spread Density functional
The authors are pleased to acknowledge fruitful conversations with M. Cole on the physics of the phenomenological approximation, and interesting discussions with F. Ancilotto during the first stages of the calculations. This work was performed with partial support from grants PIP 0546 from CONICET, UBACYT 01/K156 from University of Buenos Aires and PICT 2011/1217 from ANPCYT, Argentina.