INTERACTIONS BETWEEN SALIVARY FILMS ADSORBED ON MICA SURFACES

Due to their key importance for the understanding of intraoral events such as adhesion friction and wear, interactions between salivary film s adsorbed on mica surfaces were investigated using the interferometri c surface force technique. The films were formed by spontaneous adsorp tion to mica from 10% solutions of human mixed saliva in 1 mM NaCl. Th e buildup of the films was time dependent and reached a plateau after approximately 4 h at the experimental conditions. Forces between adsor bed films were found to be purely repulsive and to be reproducible bet ween experiments involving different sampling occasions. The force ver sus distance curves could not be described by ordinary DLVO theory. Th ey showed only minor dependence on added monovalent electrolyte and di splayed increasing hysteresis with applied force pointing to a dominan t steric contribution to the interaction. The adsorbed salivary films showed a persistent ability to relax but the force versus distance bec ame less repulsive with increasing time in contact. No signs of degrad ation of the adsorbed layers were observed over the time span of the e xperiments. (C) 1997 Elsevier Science B.V.