Nematic Pancakes Revisited

Abstract

The spontaneous spreading of the 5CB nematic liquid crystal on solid substrates has been extensively studied in the last years both at the microscopic(1-4) and macroscopic(5-6) scales. The remarkable feature at the microscopic scale is the presence of a discontinuity in the thickness profile of the films. On the other hand, the spreading dynamics of macroscopic drops is quite specific. The drop first spreads like a simple liquid, and then progressively faster, while a remarkable bell-shaped profile develops at the bottom.(5-6) How the behaviors at the various scales are linked is an open question. Any answer requires reconsidering these wetting experiments deeper into the context of nematic films. More specifically, the anchoring of molecules at the interfaces(7-8) and the competition between nematic elasticity(9) and anchoring(10) must be discussed quantitatively. For the thinnest films, the problem proves to be more complex than expected and contradictory data are found in the literature. Therefore, we decided to complete our previous studies with further experiments using another compound of the cyanobiphenyls series, the 6CB in the nematic phase, and also on liquid substrates, water and glycerol. These new data confirm that the description of the thinnest nematic films is not yet fully understood.

Simulation and theory of hybrid aligned liquid crystal films

“…As such, it represents a significant advance of the type recently called for by Delabre and co-workers [7]. In the systems we investigated, the theory appears able to describe the discontinuous structural transition between the two main hybrid-anchored states, although the critical thickness is overestimated.…”

“…This was initially interpreted in terms of competition between elasticity and van der Waals forces [5], though an alternative explanation based on fluctuation-induced interactions was also proposed [6]. Very recently, a more comprehensive experimental study of such systems has been undertaken [7], which 2 concluded that neither of these theoretical descriptions is robust for film thicknesses below 50 nm. Instead,the authors of [7] called for a theoretical description capable of recognising the molecular structure within such film.…”

“…Very recently, a more comprehensive experimental study of such systems has been undertaken [7], which 2 concluded that neither of these theoretical descriptions is robust for film thicknesses below 50 nm. Instead,the authors of [7] called for a theoretical description capable of recognising the molecular structure within such film. We address this directly in this paper.…”

Capillary-induced giant elastic dipoles in thin nematic films

“…Thick films are expected to show a simple and homogeneous structure in the layer plane (defining a 2D c director sketched in Fig. 1B) but when the thickness h decreases to a fraction of microns, a spatial xy modulation of the director field and periodic domain patterns, due to an elastic instability, are observed (22,23). We checked that the particle-free films deposited on PVA/water behave similarly.…”

Anchoring transitions and periodic deformations in nematic slabs

“…Stripe patterns in achiral centrosymmetric materials have been observed in a rich variety of physical systems: magnetic films, [2] freestanding smectic films, [3][4][5] ultrathin prefreezing smectic, [6] nematic films. [7][8][9][10][11] Nematic liquid crystals are liquids formed by anisometric molecules. The intermolecular forces acting among the molecules are such to induce a parallel orientation of the molecular long axes.…”