Effect of Orientational Fluctuation on Nematic-Smectic A Transition in the System of Hard Rod Molecules

Hosino, Masahito; Nakano, Huzio; Kimura, Hiroyuki

doi:10.1143/jpsj.47.740

Cited by 39 publications

(11 citation statements)

References 7 publications

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“…Second, it is a density functional theory ͑DFT͒ ante litteram, which provides the exact free energy expression for this particular system. 3 The idea that shape anisotropy is the sole ingredient necessary for the appearance of liquid-crystalline phases was confirmed by later theoretical calculations 4,5 and computer simulations. 6 These studies showed not only that a nematic phase can be thermodynamically stable even in systems of hard body particles of moderate aspect ratio ͑͒, but also that partially positionally ordered phases, such as smectic ͑S͒ and columnar phases, can be generated in such systems.…”

Section: Introductionmentioning

confidence: 90%

Smectic, nematic, and isotropic phases in binary mixtures of thin and thick hard spherocylinders

Cinacchi

Martı́nez-Ratón

Mederos

et al. 2006

The Journal of Chemical Physics

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A second-virial Onsager theory, based on Parsons-Lee rescaling and suitably extended to deal with multicomponent systems and smectic phases, has been used to calculate the phase diagram of a collection of binary mixtures of thin and thick hard spherocylinders. In particular, two types of phase diagrams are investigated. First, a number of binary mixtures where the two components have the same total length have been considered; in addition, the phase diagram of a binary mixture where the two components have the same volume has been calculated. For the particles of one of the two components, the length of the cylindrical part and the diameter have always been set equal to 5 and 1, respectively. Spherocylinders of the same total length and different diameter tend to demix considerably as soon as the diameter ratio deviates from unity. This happens especially at high pressures, when at least the phase richer in the thicker component is smectic. In the case where the two components have equal volumes, demixing is further increased due to the disparity not only in particle diameter but also in particle lengths. The incorporation of inhomogeneous layered phases is seen to alter significantly the phase diagrams calculated if only homogeneous phases are allowed, since transitions to a smectic phase often preempt those to a nematic or an isotropic phase. The apparent versatility of the recent experimental techniques suggests that the phase diagram features predicted by the theory might be also observed in real systems. ͓

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Section: Introductionmentioning

confidence: 90%

Smectic, nematic, and isotropic phases in binary mixtures of thin and thick hard spherocylinders

Cinacchi

Martı́nez-Ratón

Mederos

et al. 2006

The Journal of Chemical Physics

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“…Onsager showed that the stability of the nematic phase is determined by a competition between the orientational entropy, which favours the formation of randomly oriented isotropic phases, and the packing entropy, which promotes the alignment of the particles by enhancing the free volume. Despite the success of Onsager's and subsequent density functional theories to describe the formation of liquid-crystalline phases in systems of lyotropic colloids [13][14][15][16][17][18][19][20][21][22][23][24][25], the first unequivocal observation of liquid-crystalline phases by essentially exact numerical computer simulation methods had to wait until the mid1980s. The pioneering computer simulations of Frenkel and co-workers for systems of hard anisotropic particles confirmed the earlier theoretical predictions of the formation of not only nematic and discotic orientationally ordered phases in rod-like and disc-like particles but also of stable smectic (layered) and columnar (stacked) phases [1,11,[26][27][28][29][30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%

Nanorings in planar confinement: the role of repulsive surfaces on the formation of lacuna smectics

2018

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We study the structure and liquid-crystalline phase behaviour of a model of confined non-convex circular soft-repulsive nanorings in a planar slit geometry using molecular-dynamics simulation. The separation distance between the structureless parallel soft-repulsive walls is made large enough to allow for the formation of a distinct bulk phase in the central region of the box which is in coexistence with the adsorbed fluid thus allowing the analysis of single-wall effects. As the density of the particles is increased, the fluid adsorbs (wets) onto the planar surfaces leading to the formation of well-defined smectic-A layers with a spacing proportional to the diameter of the rings. An analysis of the nematic order parameter at distances perpendicular to the surface reveals that the particles in each layer exhibit anti-nematic behaviour and planar (edge-on) anchoring relative to the short symmetry axis of the rings. This behaviour is in stark contrast to the behaviour observed in convex disc-like particles that have the tendency to form nematic (discotic) structures with homeotropic (face-on) anchoring. The smectic phases formed by nanorings in the bulk and under confinement are characterised by the formation of low-density layered liquid-crystalline states with large voids, referred to here as lacuna smectic phases. In contrast to what is typically found for confined liquidcrystalline systems involving convex particles, no apparent biaxiality is found for nanorings in planar confinement. We argue that formation of the low-density lacuna smectic layers with planar anchoring is a consequence of the non-convex shape of the circular rings that allow for interpenetration between the particles as observed for nanorings under bulk conditions [C. Avendaño, G.

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“…9,10 The role of shape alone has been extensively explored by considering particles that interact purely via repulsive interactions. [11][12][13][14][15][16][17][18][19][20][21][22] Computer simulations of hard-core particle models have played a significant role in understanding the mechanism behind the organisation of colloidal systems.…”

Section: Introductionmentioning

confidence: 99%

Phase behaviour and gravity-directed self assembly of hard convex spherical caps

McBride

Avendaño

2017

Soft Matter

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We investigate the phase behaviour and self-assembly of convex spherical caps using Monte Carlo simulations. This model is used to represent the main features observed in experimental colloidal particles with mushroom-cap shape [Riley et al., Langmuir, 2010, 26, 1648. The geometry of this non-centrosymmetric convex model is fully characterized by the aspect ratio χ * defined as the spherical cap height to diameter ratio. We use NPT Monte Carlo simulations combined with free energy calculations to determine the most stable crystal structures and the phase behaviour of convex spherical caps with different aspect ratios. We find a variety of crystal structures at each aspect ratio, including plastic and dimer-based crystals; small differences in chemical potential between the structures with similar morphology suggest that convex spherical caps have the tendency to form polycrystalline phases rather than crystallising into a single uniform structure. With the exception of plastic crystals observed at large aspect ratios (χ * > 0.75), crystallisation kinetics seem to be too slow, hindering the spontaneous formation of ordered structures. As an alternative, we also present a study of directing the self-assembly of convex spherical caps via sedimentation onto solid substrates. This study contributes to show how small changes to particle shape can significantly alter the self-assembly of crystal structures, and how a simple gravity field and a template can substantially enhance the process.

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Effect of Orientational Fluctuation on Nematic-Smectic A Transition in the System of Hard Rod Molecules

Cited by 39 publications

References 7 publications

Smectic, nematic, and isotropic phases in binary mixtures of thin and thick hard spherocylinders

Smectic, nematic, and isotropic phases in binary mixtures of thin and thick hard spherocylinders

Nanorings in planar confinement: the role of repulsive surfaces on the formation of lacuna smectics

Phase behaviour and gravity-directed self assembly of hard convex spherical caps

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