Interactions between paper and adsorbed molecules

Abstract

We have studied the geometry and energy involved in the interactions between adsorbed molecules and paper substrate, over a wide range of partial pressures. A two-dimensional virial equation of state was employed to evaluate the extent of interactions by the compressibility factor (Z). Data of H-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 exceeds 1, showing a deviation from ideality due to interactions, and reaches a maximum at a value close to the BET monolayer.

As preliminary results we have measured by means of a differential microcalorimeter (Calvet) at 25‡C the energy of interactions of water andn-heptane vapor on chromatographic grade Whatman paper.

At very low coverage, the differential heats of adsorption of water on paper are higher than those ofn-heptane adsorption on paper: 114 kJ mol⁻¹ > 77 kJ mol⁻¹. During the whole process of adsorption, in the first case, the specific interaction predominates, while in the second non-specific interactions predominate i.e. the dispersion or Van der Waals forces.