Innovative Method for Laponite Encapsulation into Polymer Latex Particles by Clay Cluster-Seeded Emulsion Polymerization

We herein report an innovative pathway for the encapsulation of Laponite platelets into polymer nanoparticles via free radical polymerization in heterogeneous aqueous medium. Hydrophobization of the Laponite platelets was performed via double functionalization of the clay basal surfaces and edges by a cationic surfactant and an organosilane, respectively. The hydrophobized platelets were then dispersed in toluene and ultrasonicated with an aqueous solution of an anionic surfactant to form clay-loaded toluene droplets. The droplets were subsequently transformed into clusters by toluene evaporation and finally encapsulated into polymer latex particles using a seeded-emulsion polymerization process. Two different copolymers were synthesized: poly­(styrene-co-methyl acrylate), as a model system and poly­(vinylidene chloride-co-methyl acrylate), a specialty film-forming copolymer. Stable composite particles with a diameter ranging from 150 to 180 nm were obtained for both copolymers. Transmission electron microscopy analysis showed that the Laponite clay platelets were successfully encapsulated into the polymer latex particles. The films cast from the composite suspensions of poly­(vinylidene chloride-co-methyl acrylate)/clay particles showed spherical inclusions of clay tactoids dispersed within the polymer matrix.