Effects of gold nanoparticle film morphology on the alignment of a nematic liquid crystal

• Published in: Liquid crystals Vol. 42; no. 4; pp. 497 - 505
• Main Authors: Meli, M.-Vicki, Lardner, Michael J., Taweel, Ashley M.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 03.04.2015; Taylor & Francis Ltd
• Subjects: Alignment; Alkanes; alkanethiol; Anchoring; areal density; film morphology; Gold; Langmuir films; Langmuir-Blodgett films; LC-aqueous interface; Liquid crystal polymers; Liquid crystals; Nanoparticles; Nanostructure; Phase transitions
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/02678292.2014.1002548

We report the alignment of liquid crystal (LC) 4-cyano-4ʹ-pentylbiphenyl (5CB) to well-defined films of alkanethiol-capped gold nanoparticles, residing at the LC/water interface and in optical sandwich cell configurations. Gold nanoparticles (AuNPs) of two core sizes (2.6 and 4.1 nm) were synthesised with a variety of alkyl chain lengths (C n H 2 n +1 SH, for n = 5-18). Langmuir films of the nanoparticles were compressed to 10 mN/m and introduced to the LC/water interface via Langmuir-Schaefer transfer onto an ~20 μm thick film of LC. The 4.1 nm AuNP films consistently yield homeotropic alignment of the LC while the 2.6 nm AuNP films yield mixed alignments. These observations reflect differences in the AuNP film morphology, surface coverage and relatively weak anchoring strength of 5CB to the nanoparticle films. We determine the anchoring of 5CB to these alkanethiol-capped AuNP films at high coverage. This method can be applied to other types of nanoparticles and ligand shells for determining the LC anchoring to condensed films of water-insoluble nanoparticles with the goal of controlling nanoparticle-LC interactions.