Methane and krypton adsorption measured on single-walled nanotubes at 78.7 and 77.3 K, respectively,
give rise to stepwise isotherms, representative of the adsorption on two types of comparatively uniform
patches during the first stages of the adsorbate condensation. The values of the methane isosteric heat
of adsorption on these two fractions of quasi-uniform surface, determined from the dependence of the
equilibrium pressure on temperature between 78 and 110 K, are in very good agreement with those
measured at 77.3 K by means of isothermal microcalorimetry in quasi-equilibrium. Their respective mean
values (18.3 ± 1 and 11.2 ± 0.5 kJ mol-1) enclose that of methane adsorption on graphite in the monolayer
range (14.9 kJ mol-1). A phase transition occurring in the adsorbed film on the less attractive quasi-uniform part of the surface can be predicted from volumetric measurements.
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