Synthesis and Self-Assembly of Amphiphilic Janus Laponite Disks

Materials with asymmetric structures are attractive for wide applications in chemistry and materials science. Two-dimensional Janus disks or nanosheets are particularly appealing because of the unique shape and the distinctive self-assembled structures. A facile and versatile method for the synthesis of amphiphilic Janus Laponite disks is proposed in this paper. Positively charged PS spheres were prepared by ATRP emulsion polymerization. Upon addition of aqueous dispersion of negatively charged Laponite disks into PS emulsions, the nanosized disks were adsorbed onto the surface of PS particles via electrostatic interaction. One side of a Laponite disk touches the surface of a colloidal particle, and the other side faces the medium. After addition of positively charged polymeric micelles or quaternized poly(2-(dimethylamino)ethyl methacrylate) (q-PDMAEMA) chains into the aqueous dispersions of the colloidal particles, the micelles or polymer chains were immobilized onto the Laponite disks, and Janus disks were produced on particle templates. After centrifugation and redispersion of the colloidal particles into a good solvent, amphiphilic Janus Laponite disks with PS chains on one side and hydrophilic q-PDMAEMA or polymeric micelles on the other side were obtained. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to characterize the Janus disks. Self-assembly of the Janus disks at liquid-liquid interface and in selective solvents was investigated. Similar to small molecular surfactants, the amphiphilic Janus disks can self-assemble at liquid-liquid interface, resulting in a decrease of the interfacial tension and emulsification of oil droplets in water. In a THF-methanol mixture at a volume ratio of 1:6, PS brushes on the Janus disks collapse forming two-layer face-to-face stacks. The distinctive self-assembled structures were analyzed by TEM and AFM.