Miscibility and Alignment Effects of Mixed Monolayer Cyanobiphenyl Liquid‐Crystal‐Capped Gold Nanoparticles in Nematic Cyanobiphenyl Liquid Crystal Hosts

Abstract

Against the rule: Liquid crystal hosts (5CB and 8CB) are doped with different thiol decorated gold nanoparticles (see figure). The "simple" hexanethiol and dodecanethiol capped nanoparticles (Au1 and Au2) are more compatible to the nematic cyanobiphenyl liquid crystals than nanoparticles capped simultaneously with alkylthiols and a nematic cyanobiphenyl thiol (Au3 and Au4).This study focuses on the miscibility of liquid crystal (LC) decorated gold nanoparticles (NPs) in nematic LCs. To explore if LC functional groups on the gold NP corona improve the compatibility (miscibility) with structurally related LC hosts, we examined mixtures of two LC hosts, 5CB and 8CB, doped at 5 wt % with different types of gold NPs. Four alkanethiol-capped NPs were synthesized; two homogeneously coated with alkanethiols (Au1 with C(6)H(13)SH and Au2 with C(12)H(25)SH), and two that were additionally capped at a different ratio with a mesogenic cyanobiphenyl end-functionalized alkanethiol HS10OCB (C(6)H(13)SH + HS10OCB for Au3 and C(12)H(25)SH + HS10OCB for Au4). Investigating these mixtures in the bulk for settling of the NPs, and in thin films using polarized optical microscopy (POM) between untreated glass slides as well as POM studies and electro-optic tests in planar ITO/polyimide test cells, reveal that the alkanethiol capped NPs Au1 and Au2 are more compatible with the two polar cyanobiphenyl hosts in comparison to the NPs decorated with the cyanobiphenyl moieties. All NPs induce homeotropic alignment in 5CB and 8CB between untreated glass slides, with Au1 and Au2 showing characteristic birefringent stripes, and Au3 and A4 exhibiting clear signs of aggregation. In rubbed polyimide cells, however, Au3 and Au4 fail to induce homeotropic alignment and show clear signs of macroscopic aggregation.

Facet-dependent Cu2O nanocrystals in manipulating alignment of liquid crystals and photomechanical behaviors

“…This phenomenon is the same as that observed in the nematic LC system doped with Cu 2 O nanocrystals, which is in accordance with our assumption that the alignment of LCs can be regulated by Cu 2 O nanocrystals and is closely related to the interfacial interaction between Cu 2 O nanocrystals and LCs. Remarkably different from previous reports, in which the homeotropic orientation of LCs was induced by nanomaterials with small size (D < 150 nm), such as gold and nickel nanospheres and quantum dots, because of their high surface energy [20][21][22][23], the homeotropic orientation can be induced by Cu 2 O octahedra or rhombic dodecahedra with much larger size (D ~ 600 nm) because of their strong interface interaction with the cyano group of LCs that make them easy to disperse in LCs. Compared with other nanomaterial-doping LC systems, the surface characteristics of Cu 2 O nanocrystals can be simply controlled without complicated chemical modifications to manipulate the orientation of LCs.…”

Electric‐Field‐Induced Viscosity Change of a Nematic Liquid Crystal with Gold Nanoparticles

“…This phase sequence was also supported by the results reported in the literature. [25,26] The gold nanoparticles covered by normal alkyl chains and LC thiol compounds were characterized by 1 H NMR spectrosco-[a] Dr. …”

Liquid Crystal-Gold Nanoparticle Hybrid Materials

“…For example, nematic cyanobiphenyl end-functionalized alkylene thiol covered GNPs and its mixing with n-alkyl thiols (n = 6, 12) in two cyanobiphenyl nematic LC hosts (5CB and 8CB) were investigated [60]. By adding small quantities of alkyl thiolate-capped GNPs there was effectively reversed nematic LC orientation which further showed opto-electronic responses [61].…”