Polymer-brush-decorated colloidal platelets: precision synthesis and self-assembly
Self-assemblies of fine particles have attracted much interest from both fundamental and applied perspectives; however, the development of new strategies for particle synthesis is still required in order to broaden the research field. To this end, we synthesized colloidal platelets grafted with polymer brushes through a method that combines hydrothermal-crystallization and controlled-polymerization processes. First, we prepared pseudohexagonal aluminum hydroxide (gibbsite) platelets (GPs) that exhibited a narrow size distribution, with an average width of 700 nm and an average thickness of 40 nm. The surfaces of the GPs were modified with 2-bromoisobutyryl groups, which acted as initiators for atom transfer radical polymerization (ATRP), using a silane coupling agent with an ATRP initiation site. These ATRP-initiator-functionalized GPs were then subjected to surface-initiated ATRP with methyl methacrylate (MMA), which produced poly(MMA) (PMMA) grafts with targeted molar masses and narrow molar-mass distributions; the average graft density was 0.3 chains per nm2. The PMMA-brush-decorated GPs were completely dispersible in a variety of solvents that dissolve PMMA without the formation of any aggregates. Lyotropic liquid crystals were formed in suspensions of hybrid platelets bearing grafted chains of appropriate lengths owing to the anisotropic structures of these particles. In addition, the hybrid platelets formed a matrix-free thin film, in which the hybrids were oriented in a specific direction with a constant interplatelet distance.