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Tilt, Polarity and spontaneous symmetry breaking in liquid crystals

Tilt, Polarity and spontaneous symmetry breaking in liquid crystals
A. G. Vanakaras, D.J. Photinos and E. T. Samulski, Phys. Rev. E, 57(5), R4875-R4878 (1998).

Abstract: We show through explicit molecular modeling how tilt may be induced in layered mesophases and propagate across the-layers, using a concrete representation of flexible tail-core-tail calamitic mesogens in conjunction with-the variational cluster expansion. The results demonstrate that spontaneous symmetry breaking observed in smectic-liquid crystals-the tilt of the director relative to the layers-can be induced by excluded. volume interactions, both in the synclinic and in the anticlinic configurations.

Hydrogen bonding and phase biaxiality in nematic rod-plate mixtures

Hydrogen bonding and phase biaxiality in nematic rod-plate mixtures
A. G. Vanakaras, S. C. McGrother, G. Jackson and D. J. Photinos, Molec.Cryst. Liq. Cryst., 323, 199 (1998).

Abstract: The possibility of using H-bonding interactions to promote the stabilization of phase biaxiality in nematic binary mixts. of oblate and prolate thermotropic mesogens is discussed. Onsager’s theory of the isotropic-nematic transition was extended to allow for such selective assocns. among unlike species and it is used to calc. the phase diagram of binary mixts. consisting of hard spherocylinders and cut spheres. Directional, short-ranged attractions between rods and disks strongly stabilize the biaxial nematic mixt. against demixing and suggest that interactions of H-bonding type may provide an efficient mechanism for sustaining phase biaxiality in binary mixts. of real thermotropic nematogens. Preliminary Monte Carlo simulations designed to test such predictions are discussed.

Theory of biaxial nematic ordering in rod-disc mixtures revisited

Theory of biaxial nematic ordering in rod-disc mixtures revisited
A. G. Vanakaras and D.J. Photinos, Molec.Cryst. Liq. Cryst., 299, 65-71 (1997).

Abstract: We use the variational cluster approximation to study the relative thermodynamic stability of the spatially uniform phases of binary mixtures of hard rods and discs. The factors promoting the stability of the biaxial nematic phase are identified and discussed. The results suggest that a stable thermotropic nematic biaxial mixture cannot be obtained from molecules of the sizes and electric dipole interaction strengths commonly encountered in real calamitic and discotic thermotropic phases.

Electric dipoles and phase stability in nematic liquid crystals

Electric dipoles and phase stability in nematic liquid crystals
A. G. Vanakaras and D.J. Photinos, Mol. Phys., 85(6), 1089-1104 (1995).

Abstract: A theory for the nematic-isotropic (N-I) phase transition of prolate uniaxial molecules with longitudinal dipole moments is presented. The theory is based on the variational cluster expansion, truncated after the two-molecule term, and is implemented for polar hard spherocylinders with and without attractions, and for polar linear arrays of Lennard-Jones interaction centres. We find that the dipole interactions substantially shift the N-I transition temperature and strongly promote antiparallel molecular association, but have a weak effect on the order parameters, the pressure, and the N-I coexistence densities. The effect of dipoles on phase stability is very sensitive to their position within the molecular frame. Off-centre dipoles are shown to give rise to phase re-entrance according to the sequence N-I-N on heating at constant density. The theory does not predict a stable ferroelectric nematic phase. Continue reading

Welcome

Welcome to the home page of the Soft Matter Theory and Simulations Group of the University of Patras.

The group includes scientists from the Departments of Materials Science and Physics whose research interests are in the fields of liquid crystals, polymeric interfaces, self-organising dendrimers and dendronised polymers. Ongoing research activities cover molecular theory and computer simulation studies of:

  • specific molecular interactions and polymorphism of small molar mass liquid crystals
  • molecular modeling and phenomenology of tilted smectics and ferroelectric liquid crystals
  • biaxial nematics
  • fullerene containing liquid crystals
  • massive molecular flexibility in liquid crystalline oligomers and dendrimers
  • structure and nanomechanics of dendronised polymers
  • novel ordered fluid phases based on molecular shape non convexity
  • self-assembly properties of Janus particles, 2D nanopatterning

Research Projects

  • Biaxial Nematic Displays (BIND), EU-FP7 / ITC-1-3.2 / STREP-CP-FP-INFSO.
  • Functional LC Dendrimers: Synthesis of New Materials, Resource for New Applications (DENDREAMERS), Marie Curie Actions, EU-FP7-PEOPLE-ITN.
  • Self–organized Nanomaterials for tailored optical and electrical properties (NANOGOLD), EU-FP7-NMP-2008-2.2-2
Slide 27

Biaxial Nematic Displays, FP7 / ITC-1-3.2 / STREP-CP-FP-INFSO