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.

The structural and dynamic properties of confined water in AlPO 4 -5 zeolite (Ø ) 7.3 Å) have been investigated by neutron scattering experiments during the adsorption process. Our aim is to elucidate the peculiar behavior of confined water at the nanoscopic confinement range. Confined water presents unusual properties in comparison with other sorbate species such as deuterium or methane. Even in the nanoporous diameter range, the water sorption phenomenon looks like the so-called "capillary condensation" phase transition or the "drywet" transition. Furthermore, the sorbed water quantity in AlPO 4 -5 channels is exceptionally large. Our structural and dynamic results clearly show that the so-called "capillary condensation" step observed in the sorption isotherm is the signature of a crystallization phenomenon at room temperature (T ) 300 K). It corresponds to the growth of two helices of ice of high density (d ) 1.2) that is driven by structural commensurability with the AlPO 4 -5 channel structure.