Category Archives: Paper

Liquid crystalline phases and demixing in binary mixtures of shape-anisometric colloids

S. D. Peroukidis, A. G. Vanakaras and  D. J. Photinos, J. Mat. Chem.20, 10495-10502, (2010). (pdf) Continue reading


Extending the Maier-Saupe theory to cybotactic nematics

S. Droulias, A.G. Vanakaras, D.J. Photinos,  Liquid Crystals37:6, 969-976, (2010). e-Reprint

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Two-Dimensional Ordered Porous Patterns by Molecular Design

G.A. Tritsaris and A.G. Vanakaras, Langmuir, 26(11), pp 7808–7812 (2010); DOI: 10.1021/la904613j.  (pdf),  and supporting information.

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Symmetries and allignement of biaxial nematic liquid crystals.

P.K. Karahaliou, A.G. Vanakaras and D.J. Photinos, J. Chem. Phys., 131, 124516 (2009).

Abstract: The possible symmetries of the biaxial nematic phase are examined against the implications of the presently available experimental results. Contrary to the widespread notion that biaxial nematics have orthorhombic symmetry, our study shows that a monoclinic C2h symmetry is more likely to be the case for the recently observed phase biaxiality in thermotropic bent-core and calamitc tetrapode nematic systems. The methodology for differentiating between the possible symmetries of the biaxial nematic phase by NMR and by IR spectroscopy measurements is presented in detail. The manifestations of the different symmetries on the alignment of the biaxial phase are identified and their implications on the measurement and quantification of biaxiality as well as on the potential use of biaxial nematic liquid crystals in electro-optic applications are discussed. ©2009 American Institute of Physics

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

S.D. Peroukidis, P.K. Karahaliou, A.G. Vanakaras and D.J. Photinos, Liq. Cryst., 36(6), 727-737 (2009).

Abstract: We studied the symmetry and spatial uniformity of the orientational order of the biaxial nematic phase in the light of recent experimental observations of phase biaxiality in thermotropic bent-core and calamitic-tetramer nematics. Evidence is presented supporting monoclinic symmetry, instead of the usually assumed orthorhombic symmetry. The use of deuterium nuclear magnetic resonance to differentiate between the possible symmetries is described. The spatial aspects of biaxial order are presented in the context of the cluster model, wherein macroscopic biaxiality can result from the field-induced alignment of biaxial and possibly polar domains. The implications of different symmetries on the alignment of biaxial nematics and on the measurements of biaxial order are discussed in conjunction with the microdomain structure of the biaxial phase.

Thermotropic biaxial liquid crystals: Spontaneous or field stabilized?

A.G. Vanakaras and D.J. Photinos, J. Chem. Phys., 128, 154512 (2008). e-Reprint

biaxial clusters Abstract: An intermediate nematic phase is proposed for the interpretation of recent experimental results on phase biaxiality in bent-core nematic liquid crystals. The phase is macroscopically uniaxial but has microscopic biaxial, and possibly polar, domains. Under the action of an electric field, the phase acquires macroscopic biaxial ordering resulting from the collective alignment of the domains. A phenomenological theory is developed for the molecular order in this phase and for its transitions to purely uniaxial and to spontaneously biaxial nematic phases.

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

S.D. Peroukidis, A.G. Vanakaras and D.J. Photinos, J. Phys. Chem. B , 112(40), 12761-12767 (2008). (e-print)

biaxial clusters

Abstract: The molecular cubic-block model [J. Chem. Phys. 2005, 123, 164904] is used to study a class of poly(benzyl ether) fullerodendrimers that have recently been reported to form columnar liquid crystal phases. In agreement with experiment, the model-molecules are found to self-assemble into columns which form hexagonal or rectangular lattices. The columnar cross sections are elongated in the rectangular phase. Transitions to the isotropic phase, either directly or through the intermediate formation of smectic phases, have been found. The effects of dissolving small amounts of nonbonded fullerene molecules have been explored. The results predict that the fullerene solutes restrict the range of stability of the columnar phase and may induce transitions from the columnar to the smectic or the isotropic phase.  ©2008 American Chemical Society

Related Works:
A simple theory of molecular organization in fullerene containing liquid crystals, S. D. Peroukidis, A. G. Vanakaras and D. J. Photinos, J. Chem. Phys., 123, 164904 (2005).
Self-organisation of fullerene-containing conical supermesogens, S. D. Peroukidis , A. G. Vanakaras and D. J. Photinos, Soft Matter, 4, 493-499 (2008).
Molecular Theory of Dendritic Liquid Crystals: Self-Organization and Phase Transitions, A. G. Vanakaras and D. J. Photinos, J. Mater. Chem. 15, 2002-2012 (2005).