Coupling of the plasmon resonances of chemically functionalized gold nanoparticles to local order in thermotropic liquid crystals

We report that surface-induced ordering of liquid crystals in the vicinity of chemically functionalized gold nanoparticles leads to changes in the localized surface plasmon resonance (LSPR) of the gold nanoparticles. Gold nanoparticles with sizes between 10 and 40 nm were prepared on surfaces and chemically functionalized with organic monolayers that are known to lead to planar and homeotropic orientations of micrometer-thick films of nematic 4-pentyl-4'cyanobiphenyl (5CB) supported on continuous gold films. By measuring the absorption of light caused by the LSPR of the nanoparticles as a function of surface chemistry of the nanoparticles and temperature, we observed changes in the LSPR caused by surface-induced, localized ordering of the 5CB in the vicinity of the nanoparticles. Comparison of the far-field orientation of the liquid crystal and the LSPR behavior of the nanoparticles provides insights into the nanoscopic origins of the bulk anchoring behaviors of the liquid crystal. These results and others presented in this paper indicate that the LSPR properties of nanoparticles can be exploited to investigate how the chemical functionality of nanoparticles changes the local ordering of liquid crystals.