On the tricritical point of the nematic–smectic A phase transition in liquid crystals

Using the Landau expansion simple formulas are found that allow for systematic calculations of the tricritical temperature for a given molecular model. The theory is applied to some molecular models of the nematic–smectic A (NA) phase transition of liquid crystals. It is shown exactly that for a large class of molecular theories the NA tricritical temperature depends only on the couplings between the two lowest order translational order parameters and the orientational degrees of freedom. The relative importance of these couplings on tricritical behavior is studied in detail in the mean‐field approximation. Numerical analysis is carried out for various molecular models of the smectic A phase including the McMillan model and its generalizations. It is shown that for an experimentally relevant class of models, the presence of second and higher order harmonics does not influence the tricritical temperature in an essential way, which means that the coupling between orientational and translational degrees of f...

[1]  L. Longa,et al.  MICROSCOPIC ONE-PARTICLE DESCRIPTION OF REENTRANT BEHAVIOR IN NEMATIC LIQUID-CRYSTALS , 1982 .

[2]  H. Nakano,et al.  Phase Transitions in the Systems of Identical Rigid Molecules in Perfect Alignment–Relations of the Smectic A and Columnar Orderings in Liquid Crystals and the Crystalline Ordering to the Molecular Shape , 1982 .

[3]  D. Guillon,et al.  X-ray investigation of the smecticAreentrant nematic transition under pressure (CBOOA) , 1980 .

[4]  M. Achard,et al.  Measurements in a pure compound exhibiting an enantiotropic reentrant nematic behavior at atmospheric pressure , 1979 .

[5]  D. Guillon,et al.  X-Ray Study and Microscopic Study of the Reentrant Nematic Phase , 1978 .

[6]  T. Lubensky,et al.  Mean-field theory of the nematic-smectic-Aphase change in liquid crystals , 1976 .

[7]  P. Sheng,et al.  Constant-coupling theory of nematic liquid crystals , 1976 .

[8]  R. Birgeneau,et al.  Spin correlations near the percolation concentration in two dimensions , 1976 .

[9]  R. Behringer,et al.  Thermodynamic properties of liquid3He-4He mixtures near the tricritical point. II. Data analysis by the scaling-field method , 1976 .

[10]  P. Cladis,et al.  Volumetric Study of the Nematic-Smectic-ATransition ofN−p−Cyanobenzylidene−p−Octyloxyaniline , 1974 .

[11]  P. Gennes,et al.  The physics of liquid crystals , 1974 .

[12]  W. L. Mcmillan,et al.  Simple Molecular Model for the Smectic A Phase of Liquid Crystals , 1971 .

[13]  K. Kobayashi.  On the theory of translational and orientational melting with application to liquid crystals , 1970 .

[14]  T. Oguchi,et al.  A Theory of Antiferromagnetism, II , 1953 .

[15]  S. Jayaraman,et al.  Evidence for a Smectic-A-Cholesteric Tricritical Point: Binary Mixtures , 1985 .

[16]  J. Thoen,et al.  Experimental Evidence for a Nematic to Smectic A Tricritical Point in Alkylcyanobiphenyl Mixtures , 1985 .

[17]  R. Birgeneau,et al.  Critical behavior at the nematic-smectic-Atransition in butyloxybenzylidene heptylaniline (4O.7) , 1983 .

[18]  L. Bata.  Advances in liquid crystal research and applications , 1982 .

[19]  J. Thoen,et al.  Temperature dependence of the enthalpy and the heat capacity of the liquid-crystal octylcyanobiphenyl (8CB) , 1982 .

[20]  A. Kloczkowski,et al.  On the stability of the isotropic phase towards nematic and smectic A formation , 1981 .

[21]  G. R. Luckhurst,et al.  The Molecular physics of liquid crystals , 1979 .

[22]  Shang‐keng Ma.  Modern Theory of Critical Phenomena , 1976 .

[23]  P. Sheng,et al.  Introduction to Liquid Crystals , 1976 .

[24]  R. Griffiths.  THERMODYNAMICS NEAR THE TWO-FLUID CRITICAL MIXING POINT IN $sup 3$He--$sup 4$He. , 1970 .