Liquid crystal-nanoparticle (LC-NP) hybrid systems endow unique properties of the LC matrix and the NP dopants, attracting attention from both research communities. A uniform, well-dispersed, and highly stable thermotropic LC-NP mixture provides the platform for further applications. In this study, two types of dendritic pro-mesogenic ligands with alkyl chains and oligo ethyl glycol (OEG) chains are designed and synthesized to facilitate incorporating NPs with different materials into the thermotropic 4-cyano-4'-pentylbiphenyl (5CB) LC. Miscibility of NPs with pro-mesogenic ligands is qualitatively characterized by polarized optical microscopy and the dendritic pro-mesogenic ligand-assisted dynamic assemblies of NPs driven by equilibrating of the matrix mesogens are captured. The stability tests monitored by UV-Vis spectroscopy and transmission electron microscopy show both dendritic ligands can significantly enhance the lifetime of NPs in the LC matrix, both in the nematic and the isotropic phase, compared with the linear pro-mesogenic ligand. In particular, Au NPs capped with OEG-chained dendritic ligands are stable in 5CB for one year at room temperature and over 10 hours at 50 °C. Changes in the transition temperature and viscosity of the LC matrix support the influence of the NP dopants on the LC matrix, showing the marriage of LC and NPs tied by dendritic pro-mesogenic ligands bring novel properties to both sides.

Design of dendritic pro-mesogenic ligands for the liquid crystal-nanoparticle hybrid system

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