Thickness-dependent phase transition in thin nematic films

Abstract

Using light scattering, the thickness dependence of the isotropic-nematic phase transition temperature Tni in a thin film of octylcyanobiphenyl (8CB) is studied in two distinct geometries: with and without strain. We observed a large stress induced shift in TNI, as a function of the film thickness d. At d~ 0.3 fim a crossover in the behavior of TNI as a function of thickness is observed, which can be attributed to a competition between strain and anchoring forces. [S1063-651X (96)

Theory of light scattering by thin nematic liquid crystal films

“…A nalytical expressions for the relaxation time o f the fluctua tio n modes n^ 1 can be derived in a sim ilar way. The de pendence o f T on d as given by (18) seems to be in agree ment w ith experiments o f W ittebrood et al [17] in the scattering geometry w ith kfz-klz= 0. The n = 0 mode is the dom inating scattering mode in this geometry.…”

“…Equations with the thickness dependence of (30a) and (30b) appear to describe the experiments of [17] reasonably. Figures 5 and 6 show the thickness dependence of the relax ation time of the tilt and twist mode with smallest qz, re spectively, according to exact numerical solutions of (29a) and (29b), to the analytical approximations (30a) and (30b), and to the approximation for infinitely thick layers.…”

“…The physics o f liq u id crystals in th in film s [1][2][3][4] and in porous m edia [5][6][7][8][9][10][11][12] has received a lot o f attention in recent years. L ig ht scattering techniques are very im portant fo r this research.…”

Confinement Effects on the Collective Excitations in Thin Nematic Films

“…For example, calorimetric and light scattering experiments in confined media indicate significant confinement-induced shifts and pretransitional phenomena at the I ! N phase transition [2][3][4][5][6], and can be rather well described with a Landau-de Gennes phenomenological theory [7,8]. On the other hand, our knowledge of the dynamics of confined nematics [9][10][11][12] is rather scarce and inconsistent, since most of the studies were done on rather complex confined systems such as nematics in aerogels or porous matrices.…”

“…We find C nylon C 1 ͑3. 4 [5]) and find W air ͑0.9 6 30%͒ 3 10 25 J͞m 2 . Our results show that, for both planar and hybrid nematic layers, the director dynamics is significantly influenced by the confinement.…”