Synthesis of Liquid Crystal Silane-Functionalized Gold Nanoparticles and Their Effects on the Optical and Electro-Optic Properties of a Structurally Related Nematic Liquid Crystal

• Published in: Chemphyschem 2014-05, Vol.15 (7), p.1381-1394
• Main Authors: Mirzaei, Javad, Urbanski, Martin, Kitzerow, Heinz-S., Hegmann, Torsten
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; dispersions; electro-optics; Exact sciences and technology; functional silanes; General and physical chemistry; Gold; Ligands; Liquid crystals; Materials science; Nanoparticles; Nanoscale materials and structures: fabrication and characterization; Optics; Other topics in nanoscale materials and structures; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Physics; Structure of solids and liquids; crystallography
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201301052

Chemically and thermally robust liquid crystal silane‐functionalized gold nanoparticles (i.e. AuNP1–AuNP3) were synthesized through silane conjugation. Colloidal dispersions of these particles with mesogenic ligands that are structurally identical (as in AuNP1, AuNP2) or compatible (as in AuNP3) with molecules of the nematic liquid crystal (N‐LC) host showed superior colloidal stability and dispersibility. The thermal, optical, and electro‐optic behaviors of the N‐LC composites at different concentrations of each gold nanoparticle were investigated. All dispersions showed lower values for the rotational viscosity and elastic constant, but only AuNP3 with a dissimilar structure between the nanoparticle ligand and the host displayed the most drastic thermal effects and overall strongest impact on the electro‐optic properties of the host. The observed results were explained considering both the structure and the density of the surface ligands of each gold nanoparticle. Stable silane shell to the rescue: Thermally and chemically robust gold nanoparticles (NPs) capped with mesogenic groups through silane conjugation show very distinct optical and electro‐optic effects in a nematic liquid crystal. Surprisingly, capping a NP with a mesogen that is structurally dissimilar to that of the host has the most drastic effect on the electro‐optic properties of the host.