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Suche nach „[N.] [Kirkman]“ hat 5 Publikationen gefunden
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    F: Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    J. Wild, K. Bartle, M. O’Neill, N. Kirkman, P. Tuffin, Thomas Stirner

    Synthesis and investigation of nematic liquid crystals with flexoelectric properties

    Chemistry of Materials, vol. 17, no. 25, pp. 6354-6360

    2005

    DOI: 10.1021/cm051682y

    Abstract anzeigen

    We describe the synthesis and characterization of a series of model nematic liquid crystals with transverse dipole moments used to study the flexoelectric effect in guest−host mixtures with commercial liquid crystal host. The flexoelectric coefficicent of the mixtures, containing only 10% by weight of the dopant, are up to 6 times higher than those of the pure hosts. The length, bend angle, and dipole moments of the molecules are systematically varied to investigate any correlations with the flexoelectric effect. We find that the flexoelectric coefficients increase with molecular length, are inversely correlated with the bend angle, and are independent of the dipole moment of the dopant. Although these findings seem to contradict predictions from dipolar flexoelectric theories, they can be reconciled by considering the properties of both the guest and host in the mixture. Thiophenes and dimesogens show particularly large flexoelectric effects. This work should inform the molecular design of new materials with enhanced flexoelectric properties.

    F: Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    N. Kirkman, W. Hagston, Thomas Stirner

    A new method for investigating the surface tension from molecular dynamics simulations applied to liquid droplets

    Computational Materials Science, vol. 30, no. 5, pp. 126-130

    2004

    DOI: 10.1016/j.commatsci.2004.01.020

    Abstract anzeigen

    A new method for investigating surface tension, using molecular dynamics simulations, is proposed. The method uses the inter-particle forces to characterise the surface region. The average particle energy in this region is then employed to evaluate the surface tension. The main advantage of the proposed method is its applicability to any surface geometry and multi-component systems. For the purpose of illustration, and in view of its practical importance, the model is then applied to spherical droplets. The droplets contain 500, 1000, 2000 and 4000 particles respectively, acting under the influence of a Lennard-Jones pair potential. The effects of temperature and droplet size on the surface tension are investigated. Finally, the calculations are compared with experimental and theoretical results in the literature

    F: Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    Thomas Stirner, W. Hagston, N. Kirkman

    Continuum modelling of hybrid-aligned nematic liquid-crystal cells: optical response and flexoelectricity-induced voltage shift

    Liquid Crystals, vol. 30, no. 9, pp. 1115-1122

    2003

    DOI: 10.1080/02678290310001594562

    Abstract anzeigen

    A continuum model is employed to study systematically the optical response of hybrid-aligned nematic (HAN) liquid crystal cells under the application of an external electric field. The influence of the flexoelectric effect is discussed for a large range of anchoring strengths at the homeotropic alignment layer. It is shown that the optical response of HAN cells is governed by a complicated interplay between the flexoelectric coefficient and homeotropic anchoring strength. In particular, the calculations reveal that, for weak homeotropic anchoring, the flexoelectric effect leads to a non-linear voltage shift of the optical transmittance as a function of flexoelectric coefficient, and gives rise to an asymmetry in the transmittance–voltage curve. Finally, a comparison of the continuum-model simulations with recent experimental observations indicates that both the flexoelectric coefficient and the anchoring strength of the nematic liquid crystal MBBA on a homeotropic polyimide alignment layer are significantly lower than previously reported.

    F: Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    N. Kirkman, W. Hagston, Thomas Stirner

    A new method for investigating the surface tension from molecular dynamics simulations applied to liquid droplets

    12th International Workshop on Computational Materials Science (CMS2002), Villasimius, Italien

    2002

    F: Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    Thomas Stirner, N. Kirkman, L. May, C. Ellis, J. Nicholls, S. Kelly, M. O’Neill, J.H.C. Hogg

    CdTe nanocrystals: synthesis, optical characterisation and pseudopotential calculation of the bandgap

    Journal of Nanoscience and Nanotechnology, vol. 1, no. 4, pp. 451-455

    2001

    DOI: 10.1166/jnn.2001.053

    Abstract anzeigen

    CdTe nanocrystals were synthesized in aqueous solution using 1-thioglycerol and 2-mercaptoethanol as surface stabilizers. The nanocrystals were characterized by means of X-ray powder diffraction and UV-vis absorption measurements. The UV-vis absorption spectra exhibit two distinct transition lines. Comparison of the experimental measurements with the results of the empirical pseudopotential calculations of the CdTe nanocrystals showed that the lower energy absorption line can be assigned to the heavy-hole exciton transition, whereas the higher energy absorption line can be attributed to the light-hole exciton transition.