Effect of Ionomeric Behavior on the Viscoelastic Properties and Morphology of Carboxylated Latex Films

The viscoelastic properties of a series of carboxylated styrene/butadiene latexes were determined using dynamic mechanical spectroscopy. The viscoelastic properties of the latex films were found to depend on the pH of the latex and the type of neutralization ions present in the latex. This change in the viscoelastic properties is explained by the change in the ionomeric characteristics of the latex and a change of morphology of the latex film as determined using transmission electron microscopy. At low pH, the low-T g (glass-transition temperature) essentially noncarboxylated bulk polymer phase is often the continuous phase with the high-T g carboxylated interfacial polymer as the dispersed phase. As the mobility of the interfacial polymer decreases with increasing ionomeric characteristic with increasing pH, the morphology changes to one in which the high-T g carboxylated interfacial polymer is the continuous phase.