Easy Preparation of Anisotropic Nanoparticles Based on an Azobenzene Liquid Crystalline Polymer

Herein an easy preparation method for anisotropic nanoparticles (NPs) is reported, in which the orientation of the composed molecules aligns at a certain direction in the particle, using a conventional reprecipitation method in combination with a microwave irradiation. The size, shape, and anisotropy of NPs strongly affect several physical properties and thus their regulation is essential for applications. Although some successful examples of size and shape regulation of NPs have been reported recently, the regulation of anisotropy is still challenging. In this study, NPs of azobenzene liquid crystalline polymer (LCP) using a conventional reprecipitation method, and then irradiation with microwave are introduced. With this treatment, the phase transition from the glassy phase to the smectic phase of azobenzene LCP is induced and the azobenzene groups are oriented at a certain direction. The anisotropy of NPs is confirmed by preparing fluorescent dye-doped NPs. The prepared NPs exhibit polarization dependence of signals in the fluorescence image, which originates from the uniaxial orientation of molecules inside NPs. Furthermore, the anisotropy of NPs can be reversibly controlled with external light or heat stimuli.