INTERACTIONS BETWEEN PAPER AND ADSORBED MOLECULES - A PRELIMINARY-STUDY AND SOME EXPERIMENTAL RESULTS

We have studied the geometry and energy involved in the interactions b etween adsorbed molecules and paper substrate, over a wide range of pa rtial pressures. A two-dimensional virial equation of state was employ ed to evaluate the extent of interactions by the compressibility facto r (Z). Data of II-bonded molecules (water and butan-1-ol) and of more weakly interacting ones (n-decane and dioxane) were selected from the literature. At low surface coverage, the compressibility factor Z exce eds 1, showing a deviation from ideality due to interactions, and reac hes a maximum at a value close to the BET monolayer. As preliminary re sults we have measured by means of a differential microcalorimeter (Ca lvet) at 25 degrees C the energy of interactions of water and n-heptan e vapor on chromatographic grade Whatman paper. At very low coverage, the differential heats of adsorption of water on paper are higher than those of n-heptane adsorption on paper: 114 kJ mol(-1) > 77 kJ mol(-1 ). During the whole process of adsorption, in the first case, the spec ific interaction predominates, while in the second nonspecific interac tions predominate i.e. the dispersion or Van der Waals forces.