Molecular Organisation and Phase-Structural States of Hybrid Metal-Mesogenic Nanosystems Based on Alkylcyanobiphenyls and their Optical Properties

Abstract
Hybrid nanosystems including silver and long-chain mesogenic derivatives of alkylcyanobiphenyls have been obtained by low temperature vacuum co-condensation of reagent vapors on cooled surfaces of quartz, KBr, CaF2 or polished copper under molecular beam conditions. Controlled thermal treatment of co-condensate samples allowed the directed formation of metal nanoparticles of definite size from 2 up to 100 nm. It was shown that the manner of temperature treatment and molecular self-organisation of different liquid crystalline phases allow to control the size and morphology of nanoparticles and their aggregates formed in the system. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) data of the samples show the formation of orientationally ordered structures in nematic mesophases. Formation of flat 2D-aggregates has been found in layered smectic mesophases. Optical absorbance spectra of silver/4-pentyl-4-cyanobiphenyl (5СВ) samples encapsulated in polymer poly-para-xylylene at 300 K contain characteristic bands of plasmon absorbance of metal nanoparticles at 420–440 and 560–600 nm. Rising of metal concentration in the sample led to the performable growth of rod-like metal particles with anisometric ratio l/d > 20 and intensive absorbance at higher wavelengths (λ > 650 nm).

Keywords: hybrid nanosystems, liquid crystals, alkyl cyanobiphenyls, silver nanoparticles, optical properties