Designed appropriately, multiphase soft-core/hard-shell latex particles can achieve film formation without the addition of a coalescing aid, while preserving sufficient film hardness. Achieving optimal performance in these materials requires an understanding of how particle morphology affects film formation and stress development in the film. In this study, soft-core/hard-shell latex particles with different shell ratios, core and shell glass transition temperatures (Tgs), and particle sizes (63–177 nm) were synthesized using a two-stage emulsion polymerization. The film formation behavior of the composite particles was investigated with cryogenic scanning electron microscopy, atomic force microscopy, and measurements of the minimum film formation temperature (MFFT). Results show that film formation was enhanced for particles with thinner hard shells, smaller particle size, and a smaller difference in Tg between the core and shell polymers. For example, the MFFT decreased and the particle deformation increased for particles with thinner shells and smaller particle sizes. Stress development during drying was characterized using a cantilever beam bending technique. A walled cantilever design was used to monitor stress development without the complication of a lateral drying front. The film formation behavior and stress development correlated well with practical paint properties like scrub resistance and gloss.
Bibliographical noteFunding Information:
Acknowledgments The authors would like to gratefully acknowledge support from the National Science Foundation under Award No. CBET 0967348, and the industrial supporters of the Coating Process Fundamentals Program. Support was also received by the National Science Foundation MRSEC and REU programs under Award Numbers DMR-0754792 and DMR-081988. Acknowledgments also go to Yan Wu, Kathleen Crawford, Derek Huang, Chris Frethem, Greg Haugstad, and Wieslaw Suszynski for their contributions to this project. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.
© 2014, American Coatings Association.
- Core–shell latex
- Film formation
- Stress development