Soft Matter Theory & Simulations Group

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.

e-print MCLC98

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.

e-print_MCLC1997

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.

e-print mol_phys95

A. G. Vanakaras and D.J. Photinos, Molec.Cryst. Liq. Cryst., 262, 463-471 (1995).

Abstract: We formulate the probability distribution of orientations and conformations of flexible chains by explicitly taking into account short range repulsions and el ectrostatic interactions with the solvent molecules. The theory is used calculate the segmental order parameters associated with proton NMR measurements on n-alkanes and to study the apparent shift of the gauche-trans energy in the nematic phase. The foundation of the modular description of chain ordering is investigated in the light of the above developments. Excluded volume and electrostatic effects on the conformation energy of dimethoxyethane are evaluated.

e-print  MCLC95

• 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

Extending the Maier-Saupe theory to cybotactic nematics
S. Droulias, A. G. Vanakaras, D. J. Photinos,  arXiv:1002.2398v1 [cond-mat.soft] (2010).

Two-Dimensional Ordered Porous Patterns by Molecular Design

Langmuir, in press (2010)

Symmetries and allignement of biaxial nematic liquid crystals

Biaxial Nematics: symmetries, order domains and field-induced phase transitions

Molecular Modeling of Liquid Crystalline Self-Organization of Fullerodendrimers: Columnar to Lamellar Phase Transitions Driven by Temperature and/or Concentration Changes

Thermotropic biaxial liquid crystals: Spontaneous or field stabilized?