Liquid crystalline phases from polymer functionalised semiconducting nanorods

Abstract

The orientation of semiconducting nanomaterials is a hot topic in optoelectronic applications. Liquid crystallinity offers the potential to orient inorganic anisotropic nanorods, if they can be solubilised sufficiently as realised by polymer functionalisation. In this work we functionalised TiO₂, SnO₂, ZnO and CdTe nanorods with PMMA, PS and PDEGMEMA (poly(diethylene glycol monomethyl ether) methacrylate) diblock copolymers containing anchor groupsvia grafting-to. The block copolymers were synthesised by RAFT polymerisation (PDI ≈ 1.2) via reactive ester diblock copolymers, which were functionalised later with anchor units polymer-analogously. The surface coverage of the nanorods (determined by TGA) is dependent on the block lengths and ratios and maximal coverage is found for short anchor unit blocks. Stable dispersions are obtained for these hairy rod hybrids and they form liquid crystalline phases at suitable concentrations in organic solvents as well as in oligomeric and polymeric matrices like oligo-PEG, oligo-PS and polymeric PDEGMEMA. Liquid crystalline textures are found in polarised microscopy images. Clearing temperatures were found to be between 60 and 230 °C depending on the length of the nanorods and the organic matrix.