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The highly chiral compound S,S-4Љ-͑methylbutyl͒phenyl-4Ј-͑methylbutyl͒ biphenyl carboxylate ͑S,S-MBBPC͒ undergoes a continuous supercritical evolution from the isotropic (I) phase to the third blue phase ͑BPI III͒. Mixtures of S,S-MBBPC and its racemate have been studied with high-resolution calorimetry capable of quantitative latent heat determinations and with optical activity measurements. Both experiments indicate that the first-order BP III-I transition line ends at a critical point when the chiral mole fraction X c Ӎ0.45. Analysis of C p and optical activity data for the near-critical mixture with Xϭ0.45 indicates meanfield behavior instead of the theoretically predicted Ising fluctuation behavior, which would be analogous to that at the liquid-gas critical point of a simple fluid. It is speculated that the Ginzburg criterion can explain this mean-field behavior since the critical regime may be too small for experimental observation, as is the case for almost all Smectic-A -Smectic-C transitions.

The article contains sections titled: Introduction to the Chiral Nematic Phase and Its Properties Formulation and Application of Chiral Nematic Liquid Crystal Mixtures Applications of Chiral Nematic Phases Classification of Chiral Nematic Liquid‐Crystalline Compounds Aspects of Molecular Symmetry for Chiral Nematic Phases Type I Chiral Nematic Liquid Crystals Azobenzenes and Related Mesogens Azomethine ( S chiff's Base) Mesogens Stable Phenyl, Biphenyl, Terphenyl, and Phenylethylbiphenyl Mesogens Ester Mesogens Derivatives of Chiral Alcohols Type II Chiral Nematic Liquid Crystals Type IIa Twin Systems Using Chiral Flexible Spacers Type IIb Materials Using Achiral Flexible Spacers and Chiral Terminal Groups Type IIc and d Materials Using One or Two Chiral Cores Type III Chiral Nematic Liquid Crystals Cholesteryl Esters Chiral Mesogens Derived from Cyclohexane Chiral Heterocyclic Mesogens Axially Chiral Liquid Crystals Axially Chiral Alkenes and Overcrowded Alkenes Allenes Tricyclo[4.4.0.0 3,8 ]decane or Twistane Derived Mesogens Sterically Hindered Biphenyl Derivatives Spirobiindane Derivatives Concluding Remarks

We present an ellipsometric study of free-standing films of a chiral smectic liquid crystal possessing the phase sequence smectic-A-smectic-C,-smectic-C-smectic-C,-smectic-CA. The various subphases of the conventional smectic4 phase, which are assumed to have different structures concerning the direction of the molecular tilt in the neighbouring smectic layers, still exist in thin films consisting of only five molecular layers. In the smectic-C= phase, in thick films structural changes occur which are not present in films thinner than = 15 layers. With the exception of the smectic-C,-smectic-CA transition, all transition temperatures increase with decreasing f i l m thickness.Introduction. -In the smectic-C (Sm-C) liquid-crystal phase the rodlike molecules are arranged in layers each of which may be regarded as a two-dimensional liquid. The director, i.e. the average direction of the long molecular axes, is inclined with respect to the layer normal by a temperature-dependent tilt angle e which may amount up to 3040". If the molecules are chiral and possess a permanent transverse dipole, a ferroelectric spontaneous polarization P , , directed along the layer planes and perpendicular to the tilt direction, is present [l] in each layer; possible applications have led to a large interest concerning these materials from both fundamental and technological points of view [2]. In many compounds, the Sm-C phase transforms at higher temperatures via a second-order transition to the smectic-A (Sm-A) phase where 8 and P, are equal to zero.For several decades, only the conventional Sm-C phase, in which the tilt direction is uniform on a microscopic scale (i.e. it is the same(l) in neighbouring layers), was known. Recently, several new smectic phases were found in the chiral compound MHPOBC [3,4]: below its Sm-A phase this compound shows four different phases which were considered as modified Sm-C structures and labelled as Sm-C,, Sm-C, , Sm-C, , and Sm-CA. To date, only (I) In the case of chiral molecules, there is, in addition to the spontaneous polarization, a helical superstructure in the director field, i.e. the tilt direction changes by a small amount when going from layer to layer.