Influence of the alkyl chain length of some mesogenic molecules on their Langmuir film formation ability

Abstract

Langmuir films of members of two homologous series, the 4-n-alkyl-49-cyanobiphenyls (nCB) for n52-14 and trans-4-n-alkyl(49-cyanophenyl)cyclohexanes (PCHn) for n52-12, have been studied by recording surface pressure/area isotherms and by Brewster angle microscopy. It has been found that the compounds with very short chains (n(3) and very long chains (n.12 for nCB, n.10 for PCHn) are unable to form compressible monolayers at the air-water interface. Other members of both series can form stable Langmuir films, but both their rigidity and stability as well as the molecular packing vary with the alkyl chain length. The isotherms and BAM images imply that the organization of the liquid crystal molecules in the films is to some extent correlated with their ability to form corresponding mesophase in the bulk: nematogenic compounds tend to form rounded droplet-like domains, whereas smectogenic compounds tend to form flat domains.

Molecular Interactions in Monolayers οf Azo Dye/Liquid Crystal Mixtures at Interfaces

“…The tilt angle ϕ for 8CB was estimated as the angle between the long axis of the rigid core of liquid crystal molecules and the normal to the water surface just before the collapse point. It is in agreement with the data given in literature [12][13][14]. From the course of the π-A isotherms for the dye/8CB mixtures it follows that the rise of π begins at smaller and smaller values as X M of the dye increases.…”

Molecular organization and aggregation in Langmuir and Langmuir-Blodgett films of azo dye/liquid crystal mixtures

“…BAM images of pure 8CB recorded in this study were similar to those described previously in the literature [10,11,13]. In the region of coexistence of the gas and liquid phases (A ³ 0.5 nm 2 ) we observed condensed monolayer is− lands in equilibrium with a foam−like structure.…”

“…The detailed analysis of BAM images of liquid crystals from 4−n− −alkyl−4'−cyanobiphenyl (nCB) and trans−4−n−alkyl(4'−cyano− phenyl)−cyclohexane (nPCH) series are given in Ref. 13.…”

“…We have used two liquid crystals: 4−octyl−4'−cyanobiphenyl (8CB) and trans−4−octyl(4'−cyanophenyl)−cyclohexane (8PCH). These liquid crystals are known as substances which are able to form homogeneous Langmuir and Langmuir−Blodgett (LB) films due to the presence of the strongly polar -CN terminal group acting as the hydrophilic part of the molecule [9][10][11][12][13].…”

Characterization of Pure and Mixed Langmuir and Langmuir-Blodgett Films of Some Fluorescent Naphthalimide Dyes

“…2B) mixtures with different molar fraction (X M ) of a dye are presented there. The π-A run for pure liquid crystals 7CB is in agreement with that given in literature [26]. Table 2 contains the characteristic values of π-A isotherms for the Langmuir films of pure dyes, 7CB and dye/7CB mixtures with different X M of a dye.…”