SYNTHESIS AND CHARACTERIZATION OF CORE/SHELL IONOMERIC LATEXES .2. SURFACE-ANALYSIS BY X-RAY PHOTOELECTRON-SPECTROSCOPY

It is generally accepted that conductometric titration is a time-dependent technique in the case of highly carboxylated latexes because of the changes in the structure of the particle surface resulting from the neutralization and the alkali swellability imparted by the carboxyl groups when titrated with an alkali. At high levels of neutralization, the diffusion of the hydroxyl groups into the shell will be much faster than at the lower levels of neutralization. Due to this changing rate of the diffusion of the hydroxyl groups into the highly alkali-swellable copolymer shell, the assignment of the carboxyl groups to the different sublevels inside the particle shell can, at best, be arbitrary. To overcome this handicap, x-ray photoelectron spectroscopy (XPS or ESCA) was used to obtain the depth profile of methacrylic acid near the surface of the particles. It is expected that by accurately characterizing the surface loading of the carboxyl groups, it will be possible to control the microphase separation process of the system. Considering the high concentration of the carboxyl groups on the surface of the core/shell latexes prepared in this study, XPS experiments were conducted to obtain the depth profile of the carboxyl groups. Angle-dependent XPS studies were performed on films derived from the core/shell latexes with different amounts of methacrylic acid in the shell layer in order to determine the compositional heterogeneities between the surface and subsurface layers. In addition, x-ray photoelectron spectroscopy was used to study the changes in the surface composition of solvent-cast core/shell latex films prepared in this study upon treatment with alkali solution. It was discovered that a large-scale migration of the carboxyl groups could occur as a result of coulombic interactions. (C) 1995 John Wiley & Sons, Inc.