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

If the potential for a boom in the global hydrogen economy is realized, there will be an increase in the need for accurate hydrogen thermodynamic property standards. Based on current and anticipated needs, new fundamental equations of state for parahydrogen, normal hydrogen, and orthohydrogen were developed to replace the existing property models. To accurately predict thermophysical properties near the critical region and in liquid states, the quantum law of corresponding states was applied to improve the normal hydrogen and orthohydrogen formulations in the absence of available experimental data. All three equations of state have the same maximum pressure of 2000MPa and upper temperature limit of 1000K. Uncertainty estimates in this paper can be considered to be estimates of a combined expanded uncertainty with a coverage factor of 2 for primary data sets. The uncertainty in density is 0.04% in the region between 250 and 450K and at pressures up to 300MPa. The uncertainties of vapor pressures and saturated liquid densities vary from 0.1% to 0.2%. Heat capacities are generally estimated to be accurate to within 1%, while speed-of-sound values are accurate to within 0.5% below 100MPa.

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Fundamental Equations of State for Parahydrogen, Normal Hydrogen, and Orthohydrogen

Developments in the foundations of statistical mechanics during the past ten years or so. The author discusses how statistical concepts enter the treatment of deterministic mechanical systems, with particular reference to trajectory instabilities and to the KAM theorem. Then he deals with large systems: the thermodynamic limit and the theory of infinite systems. Non-equilibrium statistical mechanics is covered but LC relativistic statistical mechanics is not.

https://iopscience.iop.org/article/10.1088/0034-4885/42/12/002/pdf

Foundations of statistical mechanics

Phase transitions in liquid crystals

Landau theory of the nematic-isotropic phase transition

Velocity of sound in liquid hydrogen

Measurements on the velocity of sound in argon under high pressure

Sound velocity measurements in liquid methane

We have studied the formation of a nematic layer in the isotropic phase of members of the homologous series of alkylcyanobiphenyl liquid crystals (nCB, n = 5-12) near a polyamide-coated glass surface. From the temperature dependence near the isotropic-nematic transition of the standard ellipsometric quantity δ, which is directly related to the residual birefringence, the wetting behaviour of the nematic layer was investigated using a high precision rotating analyser ellipsometer. In contrast to the results of Chen et al., who observed a wetting transition for nCB-DMOAP-glass systems, our results indicate that for the nCB-polyamide-glass configurations the wetting is always partial.

Surface-induced pretransitional order in the isotropic phase near the isotropic-nematic phase transition

We present new experimental results for the static dielectric constant as a function of temperature for the coexisting phases of the binary liquid mixtures benzonitrile-isooctane and nitroethane-cyclohexane near their consolute points. From the difference of the dielectric constants of the coexisting phases as well as from the temperature dependence of the dielectric constant in each phase, a critical exponent value β=0.325+-0.005 is obtained. The average of the dielectric constant shows curvature arising from a critical contribution with an exponent of 2β.

W. Van Dael

Papers

Velocity of sound in liquid hydrogen

Measurements on the velocity of sound in argon under high pressure

Sound velocity measurements in liquid methane

Surface-induced pretransitional order in the isotropic phase near the isotropic-nematic phase transition

Dielectric study of the two-phase region of binary liquid mixtures near the consolute point