p-アミノアゾベンゼンのセルロースジアセテートに対する収着のΔVにおける溶媒の効果

抄録

Pressure effect on the sorption equilibria of p-aminoazobenzene (pAAB) from the solutions to secondary cellulose acetate (CDA) has been investigated under pressures up to 2500 bar and at a temperature of 80°C. The solvents used were water, benzene, n-propanol, n-pentanol and n-heptanol. Under the pressures all the sorption isotherms were found to be linear and the pressure dependence of the partition coefficient, K, was analyzed in terms of ΔV, the difference in the partial molar volumes of pAAB between the polymer and the solution phases, as obtained by where R, T and P are the gas constant, absolute temperature and pressure, respectively.
ΔV was found to be independent of pressure. It was -4.8cm³/mol for the aqueous solution system, while, for the organic solvent systems, pressure had much less effect on the sorption and ΔV's were found to be much smaller in the absolute values, 0_??_-1.3cm³/mol. The negative value of ΔV found for the aqueous solution system was ascribed to the volume contraction induced by the intermolecular attractions between pAAB and CDA, which should be stronger than those between pAAB and H₂O as suggested from the large value of the partition coefficient. In contrast, for the organic solution systems, it is considered that pAAB molecule is strongly solvated by the solvents and such solvation is much likely preserved in the polymer phase swollen with the solvent, leading to a chemically similar situation around the pAAB molecule both in the solution and in the polymer phases. It was pointed out that the above explanations were in accord with our previous studies on the activation volume for the diffusion conducted with respect to the same systems.
Finally, ΔV's obtained in our studies were compared with the heat of sorption data reported on similar systems. ΔV's and ΔH°'s took negative values and a positive correlation between ΔV and ΔH° was found, which is understandable because both negative ΔV and ΔH° are induced by approaching closer with each other between nonbonded atoms in the sorption system.