Film Formation and Molecular Mixing in Acrylic Latex Blends with an Acid-Rich Oligomer

The coating industry has been interested in incorporating water-soluble polymers into latex formulations to promote coalescence and enhance the mechanical properties of the coating without using any volatile organic compounds (VOCs). In this study, we investigate the effects of blending an acid-rich oligomer (ARO1), which contains sufficient −COOH groups to dissolve in water upon full neutralization with ammonia, into latex dispersions. We carried out fluorescence resonance energy transfer (FRET) measurements to examine the polymer diffusion and molecular mixing of ARO1–latex dispersions and the resulting films. The results show that ARO1 and latex polymers are partially miscible but not completely mixed in the film, suggesting that differences in the physicochemical properties of the two components influence their compatibility and interdiffusion behavior. ARO1 acts as a retardant to coalescence in the films, reducing polymer diffusion rates and thereby affecting film formation. Atomic force microscopy (AFM) mechanical mapping and confocal microscopy further elucidate the complex interplay between blend composition and film structure, demonstrating that ARO1 enhances the mechanical properties at the film surface and promotes macroscopic phase separation at higher concentrations. Our findings show that ARO1 significantly impacts the structural arrangement within these films, forming interstitial membranes between latex nanoparticle cells or phase-separated domains. These insights improve our understanding of the role of ARO1 in modulating latex membrane microstructure and properties, paving the way for the rational design of colloidal films for diverse applications.