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.

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The thermal behaviors of latexes were studied by using MicroCal MC-2 Scanning Calorimeter which is a differential scanning micro-calorimeter capable of handling fluids under pressure. The MC-2 unit was found to be uniquely capable of measuring not only the glass transition temperatures (Tg's) of wet latexes, but also the extent of annealing (enthalpy relaxation) that has a profound impact on the deformability of latex particles and, in turn, the film formation of latexes. The effects of polar monomers, the neutralization of carboxylated latexes, and coalescing agents on the wet latex Tg's were also studied.

Water-based coating formulations contain many components, such as latex binder, pigment, dispersant, thickener, and surfactant. Complex interactions between these components affect properties of the coating in both the wet and dried states. For example, rheology of the paint is dependent on the interactions of components in the formulation. Pigment interaction can affect the degree of dispersion and, therefore, have ramifications on end use properties such as hiding and tint strength of the paint film. Isothermal titration calorimetry has been used to determine the enthalpy of interaction of the coating components. Representative examples will be given to demonstrate structure-property relationships that correlate the interactions of latex, pigment, surfactant, dispersant, and thickener with paint viscosity as well as end use performance parameters such as adhesion and tint strength.

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