As their name indicates, liquid crystals simultaneously exhibit some characteristics common to both ordinary isotropic liquids and solid crystals. This ambivalence is also found in the effects of surfaces on these systems which lead to a great diversity of phenomena. These phenomena are reviewed focusing on nematic liquid crystals which have the simplest structure among the many existing types and which have been the most extensively studied. Three main kinds of effects can be distinguished. The first concerns the perturbation of the liquid crystalline structure close to the surface. Beyond this transition region, the bulk liquid crystalline structure is recovered with an orientation which is fixed by the surface: this phenomenon of orientation of liquid crystals by surfaces is the so-called anchoring. Finally, close to bulk phase transitions, critical adsorption or wetting can occur at surfaces as is also seen in isotropic systems.

https://iopscience.iop.org/article/10.1088/0034-4885/54/3/002/pdf

Surface effects and anchoring in liquid crystals

Physics of colloidal dispersions in nematic liquid crystals

/pdf/liquid-crystals-with-variable-degree-of-orientation-4bx8558klx.pdf

Liquid Crystals with Variable Degree of Orientation

Phase transitions in liquid crystals

Scattering of X-rays and neutrons at interfaces

Landau theory of the nematic-isotropic phase transition

The birefringence of mixtures of homologues from the terminally non-polar series of p,p′-dialkylazoxybenzenes has been studied. The birefringence is used as a probe of the orientational order parameter, which is coupled to the translational (smectic) order parameter. The tricritical nematic to smectic-A point which results from this coupling is found at a McMillan ratio TAN/TNI= 0.977. This is similar to the values reported for terminally polar systems and is higher than predicated by theory. The critical exponent for the variation of the order parameter across the SA–N phase transition obeys the expected trend.

First- and second-order smectic-A to nematic phase transitions in p,p′-dialkylazoxybenzenes studied by birefringence

The X-ray reflectivity form the surface of a liquid crystal with terminally polar (cyano substituted) molecules has been studied using a high-resolution triple-axis X-ray spectrometer in combination with a synchrotron source. It is demonstrated that at the surface of the smectic A1 phase a few antiferroelectric double layers develop that can be distinguished from the bulk single layer structure. A model is developed that separates the electron density in a contribution from the molecular form factor, and from the structure factor of the mono- and the bilayers, respectively. With only a few adjustable parameters it accounts for the rather complex observed reflection curve. It shows that (i) the first molecular layer has tails up rather than heads up, (ii) the smectic order parameter of the first mono- and bilayer is saturated, (iii) the antiferroelectric bilayering does decay rather abruptly and not exponentially Etude RX de la surface d'un cristal liquide pres de la transition nematique-smectique A1. Developpement en surface de quelques doubles couches antiferroelectriques qui peuvent etre distinguees de la structure en simples couches du materiau massif

http://wimdejeu.nl/onewebmedia/all%20publications/64%20JPhysique%201986%20Gramsbergen.pdf

E. F. Gramsbergen

Papers

Landau theory of the nematic-isotropic phase transition

First- and second-order smectic-A to nematic phase transitions in p,p′-dialkylazoxybenzenes studied by birefringence

Antiferroelectric surface layers in a liquid crystal as observed by synchrotron X-ray scattering

Elastic constants of some nematic liquid crystals with banana-shaped molecules

Smectic-A1-to-nematic phase transition: X-ray diffraction of the bulk and comparison with surface structure.