Waterborne polymers have enormous potential as an environment-friendly substitute of organic solvent-borne polymers. Driven by environmental and legislative pressures, the specialty aromatic polyesters were rendered water-dispersible by functionalizing the polymer backbone with ionic monomers. Since these polyesters are designed to be used as waterborne dispersions, understanding their colloidal interactions in dispersions is critical for their application. By using a range of commercially available sulfopolyesters as a model system, we investigated the relationship between their molecular composition, colloidal interactions, and phase equilibria. As a result of being partially water-soluble, these polyesters form self-assembled nanoaggregates (20 ~ 50 nm) in water without the need for additional stabilizer(s). These nanoaggregates are composed of hundreds of polymer molecules, where their aggregation number is determined by the composition, ionic groups and molecular weight of the polymers. By using static, dynamic, and electrophoretic light scattering, we present a model for nanoaggregate formation in water based on the critical surface charge density of these nanoparticles. Since the ultimate goal of developing such waterborne system is to apply them in films and coatings, we also explored how these films interact with water by forming nanofilms of brilliant structural colors. To test the structure and properties of the dried films, we deposited sessile water drops on the films which lead to partial dispersion and evaporation-induced “coffee ring” formation. We further characterized this new class of coffee ring phenomena as “coffee ring erosion” and demonstrated that such water-damage property is governed by the ionic composition of the polyesters. Additionally, we showed that the water-resistivity and integrity of the coatings can be significantly improved by incorporating rapid thermal-curing. Such fundamental understanding of colloidal interactions could be used to efficiently control and improve the colloidal stability and film-formation ability of these polyesters. Therefore, this study may enable the design of novel high-performance volatile solvents-free and surfactant-free waterborne dispersion systems.

Revisiting the colloidal fundamentals and exploring nanofilm formation of water-dispersible polyesters

2019 Fall National Meeting

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