131,232 research outputs found
Managing banking crises in Europe after the Great Crisis
No full textContains fulltext :
231862.pdf (Publisher’s version ) (Open Access)Radboud University, 20 januari 2021Promotores : Busch, D., Ferrarini, G.XXXI, 347 p
A first principles and mean field investigation of the conformational properties of 5CB
No full textAlthough the minimum energy conformation of the mesogenic molecule 4-n-pentyl-4′-cyano-biphenyl (5CB) is known to have an inter-ring torsional angle of 37.0° and an alkyl tail which lies perpendicular to the adjoining phenyl ring, less is known about the conformational properties of the alkyl tail. This paper investigates these properties in both the gas and nematic phase by combining first principles density functional theory calculations with the surface tensor mean field model of Ferrarini et al. (Molec. Phys, 1992, 77, 1). By comparing gas and nematic phase conformer populations, it is found that the nematic mean field selectively favours and disfavours certain conformations of the tail. The conformer distribution is discussed with reference to the results of bulk simulation studies and to C—D bond order parameters measured by NMR experiments
Who’s Afraid of MiFID II?
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162827.pdf (Publisher’s version ) (Open Access
Molecular shape, elastic constants and spontaneous twist in chiral and achiral nematics: insights from a generalised Maier–Saupe framework
No full textOrdinary nematic liquid crystals have a uniform director field as ground state. However, there are relevant examples of spontaneously twisted nematic states, not only in chiral, but also in achiral materials. Different twist configurations can be found, with the director modulation along the twist axis, as in the cholesteric and in the twist-bend nematic phase, or perpendicular to it, as in blue phases and in skyrmion structures. Here, we develop a generalised Maier–Saupe theory to calculate the thermodynamic and elastic properties, included saddle-splay, of nematics made of particles whose shape can be described as a distorted rod. This turns out to be a powerful approach for screening the relation between the molecular shape and the formation of modulated nematic phases. Application to the paradigmatic models of banana-shaped and helical particles allows us to identify the role of distinct shape features, such as curvature and chirality, and the distinct mechanisms by which these promote twisted configurations
From Bend to Splay Dominated Elasticity in Nematics
No full textIn the past decade, much evidence has been provided for an unusually low cost for bend deformations in the nematic phase of bent-core mesogens and bimesogens (liquid crystal dimers) having a bent shape on average. Recently, an analogous effect was observed for the splay mode of bent-core mesogens with an acute apical angle. Here, we present a systematic computational investigation of the Frank elastic constants of nematics made of V-shaped particles, with bend angles ranging from acute to obtuse. We show that by tuning this angle, the elastic behavior switches from bend dominated (K33>K11) to splay dominated (K11>K33), with anomalously low values of the splay and the bend constant, respectively. This is related to a change in the shape polarity of particles, which is associated with the emergence of polar order, longitudinal for splay and transversal for bend deformations. Crucial to this study is the use of a recently developed microscopic elastic theory, able to account for the interplay of mesogen morphology and director deformations
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