Almost Critical Behavior of the Anchoring Energy at the Interface between a Nematic Liquid Crystal and a SiO Substrate

Abstract

The anchoring energy at the interface between the nematic liquid crystal 4-n -pentyl-4'cyanobiphenyl (5CB) and a glass plate treated by oblique evaporation of SiO is studied by measurement of the torque exerted on the surface by the nematic subject to an orienting magnetic field. The anchoring energy is sharply reduced as the clearing temperature is approached. The experiment provides the first direct evidence of a strong reduction of the surface order parameter for this system in the anisotropic phase.

Effective anchoring and scaling in nematic liquid crystals

“…The function G(−k, −q) appearing in equation (14) is defined in such a way as to be zero for |k| ≤ Λ or |q| ≤ Λ , and to coincide with the inverse of G −1 (k, q) in the high wave vectors subspace, i.e., (16) where the subscript in the integral indicates that the integration is restricted to the shell Λ < |q| < Λ.…”

“…In summary, in order to coarse-grain the harmonic free energy F [ψ], one can first express it in Fourier space according to (6), which defines the Hamiltonian G −1 (k, q), then determine the inverse G(k, q) of the latter in the high wave vector subspace according to (16), and finally obtain the renormalized Hamiltonian G <−1 (k, q) of the coarsegrained free energy F < [ψ < ] by means of equation (18). In a translationally invariant system, G −1 (k, q) is proportional to δ(k + q), which means that the different Fourier components are not coupled.…”

Alignment of nematic liquid crystals on an electrically poled photopolymer film

“…2 and W s ϭ10 Ϫ3 J/m 2 for the condition of a weak interaction between the two layers. 17 This approximation gives for the order parameter of 5CB on EPP film Sϳ10 Ϫ2 , which is 10 times smaller than S of a rubbed PI 18 but 10 times bigger than the 10 Ϫ3 of an oblique evaporated SiO layer 19 or LPUV PVCN. 20 Figure 4 shows the relative optical transmittance as a function of the angle of incidence, which was measured by the crystal rotation method 21 for two planar cells.…”

Effect of nanoconfinement on liquid-crystal polymer chains

“…As for the choice of the exponents, we recall that by integrating the dispersion interaction between a LJ particle and an infinite slab formed by LJ centres, an overall particle-surface potential governed by a (9,3) law is obtained. In the literature, the particle-surface energy is usually modelled with a variety of repulsive and attractive exponents, like the (10, 4) exponents implemented by Steuer et al, 26 and the (9, 3) used by Caprion et al 27 Considering that most common materials mentioned in the Introduction are far from being completely smooth 9,20,21 and also the existence of electrostatic interactions [13][14][15][16][17][18][19] between surfaces and molecules, we have arbitrarily set the repulsive coefficient n to a softer value of 6 to allow for some surface penetration, while keeping m = 3.…”

“…For instance, alignment perpendicular to the surface (homeotropic) can be obtained by coating, e.g. with lecithin 9 or certain polyimides, [13][14][15] while alignment in the cell plane can be obtained by mechanically rubbing a polymer deposited film, [16][17][18][19] with SiO 2 sublimation, 20,21 or with suit-able gold deposition. 4 On the other hand, untreated hydrophilic mica or a flat gold layer cause a "planar parallel" orientation 9 of the director of nematic LC.…”