Surface energy characteristics of adhesive monomers

The aim of the investigation was to determine the surface free-energy components of potentially adhesive monomer mixtures.

Four liquids with known components of surface free-energy were used as reference. Small drops of the liquids were placed on the polished surfaces of four types of solid (metal, porcelain, resin composite and hydrocarbon), and the contact angles were measured. By means of the fundamental equations for wetting, the three components of the surface free-energy of the four solids were calculated. Small drops of various monomeric mixtures were then placed on the four solid surfaces, and on the basis of the previously calculated components of surface free-energy of the solids, the surface energy characteristics of the monomeric mixtures were determined. The relationships between contact angles and composition, and between surface tension and composition, were studied by regression analyses. Comparisons between values were carried out by means of Neuman-Keuls' multiple range test at a level of statistical significance of p = 0.05.

Statistically significant differences between the monomeric mixtures as regards the wetting of the four solids were observed. These differences reflected differences in the acid or base component of the surface free-energy of the monomers. In particular, monomeric mixtures containing HEMA, MAN or 4-META exhibited a significant acid component of the surface free-energy.

Knowledge of the surface free-energy components of monomers throws light on the mechanisms associated with the adhesion of resin composites, including resin cements. A better understanding of the interfacial interactions may act as guide in a research aimed at developing resin materials of increased adhesion to metal, porcelain or resin composite.