3.2.1. Linear F-Alkyl/H-Alkyl Diblocks 1720 3.2.2. Unsaturated Diblocks 1721 3.2.3. Branched Diblocks 1722 3.2.4. Diblocks with Heteroatoms 1723 3.2.5. Diblocks with Heavy Halogens 1724 3.3. Triblocks and Multiblocks 1724 3.3.1. FnHmFn Triblocks 1724 3.3.2. HmFnHm Triblocks 1725 3.3.3. Star-Shaped Triblocks 1725 3.3.4. Multiblocks and Polyaffine Compounds 1726 4. Basic Properties of (F-Alkyl)alkyl Diblocks 1726 4.1. The “Polarity” Issues“Apolar”, yet Dipolar 1726 4.2. Surfactant Properties 1727 4.2.1. Surfactant Effects of FnHm Diblocks at Interfaces with Air, Fluorocarbons, and Hydrocarbons 1728

Chemistry, physical chemistry, and uses of molecular fluorocarbon--hydrocarbon diblocks, triblocks, and related compounds--unique "apolar" components for self-assembled colloid and interface engineering.

Critical behavior of dielectric permittivity in the isotropic phase of nematogens

Phase transitions among the rotator phases of the normal alkanes: A review

The low value of , where is the nematic-isotropic phase transition temperature and denotes the virtual transition temperature, is a long-standing puzzle in the physics of liquid crystals. The present review presents experimental and theoretical results on this long-standing problem. New experimental and theoretical results for the critical behaviour in the isotropic phase of nematogens are reviewed. We calculate in a unified approach the low value of , at both critical and tricritical points. The possibility of tricritical behaviour at the nematic-isotropic transition is also discussed by means of Landau theory. The various predictions are compared with the available experimental results.

http://iopscience.iop.org/article/10.1088/0953-8984/10/41/003/pdf

The puzzle of the nematic-isotropic phase transition

Results of studies of static dielectric permittivity (epsilon) and nonlinear dielectric effect (NDE) in the isotropic phase of 4-n-4'-isothiocyanatobiphenyl (nBT) homologous series from n = 2 to n = 10 exhibiting the isotropic-smectic E (I-SmE) transition, are presented. They are compared with results of similar studies in 4-cyano-4-n-alkylbiphenyls (nCB) from n = 4 to n = 12. In this homologous series isotropic-nematic (I-N) and isotropic-smectic-A (I-Sm-A) transitions take place. Despite significant differences between N, Sm-A, and Sm-E phases the same pretransitional behavior of epsilon and NDE in the isotropic phase, described by critical exponents gamma = 1 and alpha = 0.5, was found. It has been shown that when the length of the alkyl chain of a compound increases the discontinuity of the transition drops in nBT and rises in nCB. The influence of pressure on the discontinuity is also discussed.

Phase transitions from the isotropic liquid to liquid crystalline mesophases studied by linear and nonlinear static dielectric permittivity

A simple Landau-type free energy function is presented to describe the smectic-A-isotropic phase transition. Varying the coupling between orientational and positional order parameters, a smectic-A-isotropic or a nematic-isotropic phase transition occurs. Within this model the smectic-A-isotropic phase transition is found to be always more strongly first order than the nematic-isotropic phase transition. The theoretical results are found to be in good agreement with all published experimental results.

/pdf/simple-landau-model-of-the-smectic-a-isotropic-phase-2gtclh0nnf.pdf

Simple Landau model of the smectic- A-isotropic phase transition

We propose a Landau model to describe the smectic C–isotropic phase transition. A general Landau theory for the coupled orientational and translational order parameters and including the tilt angle is developed. The conditions for the smectic C–isotropic phase transition and the stability conditions of the smectic C phase are calculated. On the basis of this model it is argued that the smectic C–isotropic phase transition is always first order. We present a detailed analysis of the question under which conditions a direct smectic C–isotropic phase transition prevails in comparison to smectic A–isotropic and nematic–isotropic transitions. The theoretical results are found to be in qualitative agreement with all published experimental results.

Landau model of the smectic C–isotropic phase transition

The hydrodynamic theory for the smectic-$A$ phase and the isotropic phase is generalized to the macroscopic dynamics in the vicinity of the isotropic--smectic-$A$ phase transition. The macroscopic dynamic equations are presented on the isotropic side as well as on the smectic-$A$ side of the phase transition, incorporating the effect of an external electric field. Specific experiments to test some of the effects contained in the macroscopic dynamic equations are suggested.

/pdf/macroscopic-dynamics-near-the-isotropic-smectic-a-phase-g0zckz93ga.pdf

Macroscopic dynamics near the isotropic-smectic-A phase transition.

In this paper we discuss the direct isotropic to chiral smectic-C phase transition on the basis of a phenomenological theory. The model free energy is written in terms of the coupled order parameters including the spontaneous polarization. We present a detailed analysis of the different phases that can occur and analyze the question under which conditions a direct isotropic to chiral smectic-C phase transition is possible when compared to other phase transitions. On the basis of this model the isotropic-smectic-C* transition is always of first order. The theoretical predictions are compared with the available experimental results.-1

A phenomenological theory of the isotropic to chiral smectic-C phase transition

The effect of nonmesogenic solute on the nematic-smectic-A (NA) transition is examined within the Landau phenomenological theory. When nonmesogenic solute are added to a mesogenic compound consisting of both nematic and smectic-A phases, the NA transition temperature is depressed and a two phase region is formed due to the presence of the impurities of the solute. Decreasing the nonmesogenic solute to the pure compound, the first order NA transition becomes second order at the tricritical point in Landau approximation. The effects of nonmesogenic solute on the Frank elastic constants are also discussed.

Prabir K. Mukherjee

Papers

Simple Landau model of the smectic- A-isotropic phase transition

Landau model of the smectic C–isotropic phase transition

Macroscopic dynamics near the isotropic-smectic-A phase transition.

A phenomenological theory of the isotropic to chiral smectic-C phase transition

Effect of nonmesogenic solute on the nematic-smectic-A phase transition