Abstract
The heats of wetting by water of cotton cellulose containing various amounts of adsorbed and desorbed water were measured. These measurements together with those of the water vapor sorption isotherm were used to calculate the integral and differential enthalpies, free energies, and entropies of adsorption. Irreversible effects were avoided by vacuum-drying all samples at room temperature. The differential enthalpy values suggest hydrogen bonding. The differential entropies are explained in terms of changes in both the adsorbate and adsorbent.The surface area of the cellulose is calculated by applying the Brunauer–Emmett–Teller and Harkins–Jura equations to the adsorption isotherm. The changes in the differential enthalpies and entropies of adsorption follow the same sequence as the changes in film formation given by the surface area calculations.No hysteresis was observed in the heats of wetting of adsorbed and desorbed samples. It is concluded that the hysteresis of the sorption isotherm is an entropy phenomenon. This supports Barkas' explanation of hysteresis in terms of plastic deformation of a gel.
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