Heat Capacity and Heat of Adsorption of Argon Adsorbed on Graphon

Abstract

Heat capacities of argon adsorbed on Graphon were determined calorimetrically in the range 55 to 88 deg K, for surface coverages of 0.301, 0.609 and 0.921 fractions of a monolayer. The data indicate the existence of maxima at temperatures below 55 deg K, with the height of each maximum increasing as coverage decreases. The magnitude of the heat capacity at these maxima, particularly at the lowest coverage, could not be justified solely on the basis of a localized to mobile transition of the type predicted by Hill. An isosteric heat of adsorption was determined calorimetrically for this system at 87.5 deg K for surface coverages from 0.165 to 1.25 monolayers. The general shape of the curve agrees with other studies of the system amd, in particular, confirms the presence of a maximum isosteric heat of adsorptiom at about 0.75 fraction of a monolayer. This maximum is interpreted as being due to a prominence of argon-- argon interactioms on a relatively homogeneous surface.