Gel-like behavior of pH dependent latex films

Gel-like properties of soft latex particles, made of styrene-butyl acrylate statistical copolymers, were observed after forming thin films; polymer chains were not covalently linked to one another. Acrylic acid groups, inserted at random on chain skeletons of copolymer, were supposed to play the role of crosslinks. The concentration of these carboxylic acid groups, hereafter called κ COOH , was varied from 100 to 800 μmol/g; the pH of emulsions, prior to the formation of films, was given three values: 2.5, 5, and 7.5. Measurements of the gel fraction or of the swelling ratio of latex films were performed as a function of the κ COOH variable to attempt to show that this concentration determines the state of gelation