Influence of ethoxylate chain length for synperonic NPX surfactants on the film formation behaviour of methylmethacrylate-2-ethylhexyl acrylate copolymer latexes: II. A dielectric investigation

A real time dielectric relaxation investigation covering the frequency range from 10-2 to ~105Hz, on the film forming process in methylmethacrylate-2-ethylhexyl acrylate latex copolymers stabilised with nonylphenol ethoxylate is presented. The three systems investigated have essentially identical latex compositions and the only difference between these materials is the length of the ethoxylate chain in the nonylphenol ethoxylate stabiliser. The dielectric relaxation measurements allow changes in the dipolar nature of the medium to be monitored as the process of film formation and coalescence occur. Combining the dielectric data with other observations of the coalescence process reported in part 1 has allowed identification of various stages in the film formation process. It is evident that the formation of a micro-crystalline phase between the emulsion particles by the longer chain ethoxylate molecules, inhibits the coalescence process. Moreover, the stabiliser can also be seen to play a role in determining the dynamics of the molecules in the latex and a critical role in the overall coalescence process. A schematic model describing the various stages of coalescence is presented.