ROLES OF MOLECULAR-INTERACTIONS IN ADHESION, ADSORPTION, CONTACT-ANGLE AND WETTABILITY

This study is aimed at understanding the controversy between the surfa ce tension component (STC) theory and the equation of state (EQS) appr oach for interfacial tensions. We attempt to relate molecular interact ions to various components of surface tension. Molecular interactions consist of electrostatic (ES), charge transfer (CT), polarization (PL) , exchange-repulsion (EX), dispersion (DIS), and coupling (MIX) compon ents. These interactions can be the basis for the STC theory involving Lifshitz-van der Waals (LW) and the short range acid-base (AB) or don or-acceptor interaction. Each of these components is shown to contain two major parameters. New equations for the interaction energy and sur face tension for polar molecules are proposed to include the ES and EX parameters, which happen in some cases to balance each other or nearl y cancel out without being detected. The roles of molecular interactio ns on adhesion, adsorption, contact angle, and wettability are illustr ated through the spreading coefficient S, the Hamaker coefficient A, a nd Derjaguin's disjoining pressure PI(h). We have found that the STC t heory is applicable to the systems involving either physisorption or c hemisorption, while the EQS applies to those involving ony physisorpti on.