Coupling free energy and surface anchoring mechanism in gold nanorod–nematic liquid crystal dispersions

Abstract

The self-organizing properties of nematic liquid crystals (NLC) have been widely used to align anisotropic nanorods (NR) dispersed in them. The coupling interaction of the NR–NLC is an important parameter to determine the surface anchoring strength of GNRs in NLC. Herein, we have taken gold nanorods (GNRs) as a typical example to develop a method to measure the coupling free energy between the NRs and NLCs. By probing the magnetic Fréedericksz transition (MFT) thresholds of the doped-LC cells, the extraordinary increasing trend of MFT thresholds in the GNR–LC system can be explained by theory of the Landau–de Gennes free energy. The coupling coefficient γ of the binary composition and the anchoring energy W of the GNR surface were obtained by choosing proper limitations. Similarly, the MFT thresholds of gold nanospheres (GNSs) and other surfactant-capped GNR were measured for reference and comparison. In addition, response time measurements of the LC cells were carried out to prove the accuracy of the MFT thresholds. These results provide insight into the GNR–LC binary systems, and the technique can be extended to more NR–LC compositions.