THERMODYNAMIC ANALYSIS OF PIGMENT AND POLYMER SURFACES USING INVERSE GAS-CHROMATOGRAPHY

The thermodynamics of pigment particle surface-polymer interactions ha ve been characterized using inverse gas chromatography (IGC). The use of IGC in this new application extends available analysis to the calcu lation of the thermodynamic properties of reversible particle-polymer interactions. This IGC technique was used to determine solid surface e nergies of particles and polymers; free energy, enthalpy, and entropy of adsorption; and work of adhesion. Available theories to calculate t he nonpolar (dispersive) and polar contributions to these surface prop erties were reviewed and found applicable. The values obtained agree f avorably with those obtained from alternate techniques. Nonpolar force s provided a large contribution to the free energy and enthalpy of ads orption. In addition, acid-base pairs were found to undergo favorable interactions while acid-acid and base-base pairs were less likely to u ndergo strong interactions. Amphoteric adsorbates underwent extensive interactions with both acids and bases due to their mutual compatibili ty and their tendency to self-associate. Entropies of adsorption for m ost interactions were found to be negative, indicating conformational changes from the gaseous state to a more restricted adsorbed configura tion, similar to those in the condensation process. Entropy contributi ons to the total free energy change were approximately 30% of the enth alpy changes.