Formation of hierarchical platelets with morphological control by self-assembly of an azobenzene-containing liquid crystalline diblock copolymer

Abstract

The bottom-up fabrication of hierarchical assembled structures is of prominent importance to construct subtle and complex artificial systems. However, the formation of two-dimensional (2D) and three-dimensional (3D) structures with controllable morphology is still challenging, especially when using liquid crystalline block copolymers (LC BCPs). Herein, we report the preparation of a variety of hierarchical platelets with a LC azobenzene core based on the self-assembly of poly(ethylene glycol)-b-poly(6-(4-butyl-4′-oxyazobenzene)hexyl methacrylate) (PEG-b-PAzoMA) diblock copolymer via a thermal annealing process. The dimensions and morphologies of the platelets are controlled through manipulating the nucleation and aggregation by tuning the concentration and the cooling rate. It is found that PEG-b-PAzoMA diblock copolymers firstly assemble into a stacked leaf-shaped platelet structure in ethanol, and subsequent “cross” platelets and finally flower-shaped platelets by continually increasing the concentration of PEG-b-PAzoMA. Interestingly, the slow cooling rate of the heating-annealing process changes the morphology from stacked leaf-shaped platelets to 3D rectangular platelets. Besides, the azobenzene moieties undergo trans–cis isomerization upon UV irradiation and further promote a morphological revolution of the platelets. These unique 2D and 3D platelets with tunable shapes will be potential candidates for a wide range of functional materials.