The coating industry has dramatically changed since the 1950s, when organic solvent-based coatings were gradually replaced with waterborne emulsion latex polymer coatings. Waterborne coatings offer great advantages for health and the environment, but still present challenges in terms of coating performance, including water resistance, stability and surface hardness. The major obstacles to overcoming these challenges lie within the contradictions of desired properties before and after drying. For example, it is beneficial for latex particles to be attracted to water (hydrophilic) to maintain a stable dispersion prior to applying a coating to a surface. However, the opposite is desired after a coating has been applied and dried, when water repellence (hydrophobicity) is required. Therefore, a solution that can create a hydrophobic surface after drying while remaining predominantly hydrophilic in dispersion is needed to make waterborne coating technology more versatile.
Another example is the influence of glass transition temperature of the resin (Tg). For improving the film formation during the drying process, low Tg is desired. However, for improving surface hardness after paint is dried, high Tg is required. One potential solution is to stratify a layer of high-Tg binder particles to the surface of the coating layer to boost the hardness, while maintaining the majority of the bulk binder particles with lower Tg for good film formation properties. The recent development of novel Janus particles additives offers promise of addressing these challenges through a unique self-stratification process.