Submicron-sized sterically-stabilized lightly cross-linked poly(2-vinylpyridine) latexes were synthesized by non-aqueous dispersion polymerization using a hydrophobic polydimethylsiloxane macromonomer and used to prepare millimetre-sized ‘liquid marbles’. These ‘liquid marbles’ exhibited long-term stability when transferred onto the surface of liquid water provided that the solution pH was pH 4.9 or above. In contrast, the use of more acidic solutions (pH < 2.9) led to immediate ‘liquid marble’ disintegration and spontaneous dispersal of the poly(2-vinylpyridine) particles in their protonated microgel form. Moreover, the liquid marbles on the surface of water immediately disintegrated on addition of acid. Thus the critical minimum pH required for long-term ‘liquid marble’ stability correlates closely with the known pK_a value of 4.7 for poly(2-vinylpyridine) chains.

Polymer colloids are complex materials that have the potential to be used in a vast array of applications. One of the main reasons for their continued growth in commercial use is the water-based emulsion polymerization process through which they are generally synthesized. This technique is not only highly efficient from an industrial point of view but also extremely versatile and permits the large-scale production of colloidal particles with controllable properties. In this perspective, we seek to highlight the central challenges in the synthesis and use of polymer colloids, with respect to both existing and emerging applications. We first address the challenges in the current production and application of polymer colloids, with a particular focus on the transition toward sustainable feedstocks and reduced environmental impact in their primary commercial applications. Later, we highlight the features that allow novel polymer colloids to be designed and applied in emerging application areas. Finally, we present recent approaches that have used the unique colloidal nature in unconventional processing techniques.