Surface induced liquid-crystal alignment studied by optical second-harmonic generation

Abstract

Articles you may be interested inMicroscopic calculation of surface-induced second-harmonic generation in crystals of para-nitroaniline Liquid-crystal alignment on polytetrafluoroethylene and high-density polyethylene thin films studied by optical second-harmonic generationThe orientational order induced in a liquid crystal (LC) monolayer of adsorbed 4-n-octyl-4'-cyanobiphenyl molecules on rubbed substrates is studied by measuring the second-harmonic response. By systematically varying the rubbing conditions and measuring the induced LC bulk and monolayer alignment, we can conclude that the homogeneity of the LC bulk alignment and the surface in-plane order parameter of the LC monolayer are closely related. The polar and azimuthal ordering of the LC monolayer, however, are found to be decoupled. By rubbing polyimide films twice and studying other rubbed surfaces, we show that two mechanisms are responsible for the LC alignment, depending on the kind of substrate that is used. For rubbed bare glass substrates long-range elastic interactions, which do not affect the monolayer alignment, are dominant. In the case of rubbed polyimide films molecular short-range interactions are responsible for the alignment of both the LC bulk and the LC monolayer.

Mechanism of liquid crystal alignment on submicron patterned surfaces

“…[3][4][5][6][7] Although successfully applied for the past 30 years for the production of liquid crystal displays, the mechanism of the alignment of LC molecules on such a rubbed substrate is not precisely understood. According to the elastic continuum theory of Berreman 8 the rubbing induces grooves on the polymer surface and the liquid crystal molecules prefer to align parallel to the direction of the grooves.…”

In-plane Molecular Order of a Photo-oriented Polyamic Acid Film: Enhancement upon Thermal Imidization

“…À A k )= (A ? þ A k ) [9,10]. Here, Q / ¼ 0 means isotropic in-plane molecular orientation, and Q / ¼ 1 and À1 mean that all polymer chains align perpendicular and parallel, respectively, to the polarization direction of LPUVL.…”

Liquid-crystal monolayers in high magnetic fields: a second-harmonic generation study

“…T he resulting surface density of the m olecules is 2 x 1014 c m " 2, ensuring th a t the com plete S H G signal is generated by the LC molecules. F u rth e r details on the sam ple p rep aratio n an d c h aracter ization have been published elsewhere [5,6,11].…”