Cationic polyacrylamide adsorption on epoxy surfaces

The adsorption of a cationic polyacrylamide (acrylamide/β-methacryloxyethyltrimethylammonium methyl sulfate copolymer) onto an imidazole catalyzed bisphenol-A based epoxy resin surface was examined by surface wetting. The work of adhesion of diodomethane, ethylene glycol and water was measured an microscopically smooth epoxy surfaces using a Wilhemy plate method, in both advancing and receding modes. The cationic polyacrylamide was adsorbed from aqueous solutions as a function of the pH of the solution. In addition to the cationic quaternary amine groups along the polymer chain, there were carboxylate groups from amide hydrolysis, which had a pK(a) of 10.73. The surface wetting of neither diodomethane nor ethylene glycol was sensitive to the adsorbed polyacrylamide. Wetting of the surface by water was very sensitive to the presence of adsorbed polyacrylamide. Polyacrylamides in solutions below pH 9 adsorbed onto the epoxy surface resulting in increased water adhesion to the surface. When the polyacrylamide solution was greater than pH 9 carboxylate groups ionized and the anions inhibited adsorption of the polyacrylamide. The water wetting measurements were shown to correlate with the adsorption of Pd/Sn colloidal particles used for electroless deposition of copper circuit lines on printed circuit boards.