Hard Convex Body Fluids

Allen, Michael; Evans, G. T.; Frenkel, Daan; Mulder, Bela M.

doi:10.1002/9780470141458.ch1

Cited by 251 publications

(138 citation statements)

References 258 publications

(290 reference statements)

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“…However, the Gay-Berne family of anisotropic potentials employs soft ellipsoids as basic modeling units to represent whole rodlike 15 or platelike 16 (and thus usually mesogenic) molecules, in order to speed up Monte Carlo and molecular dynamics 17 calculations by giving up intramolecular detail. Other popular choices for the same purpose are soft spherocylinders; 18 soft biaxial ellipsoids, 19 hard ellipsoids and spherocylinders, 20 and several other site-site variants 21 are employed too. The use of these nonspherical convex rigid bodies has been linked traditionally to liquid crystal research [22][23][24] but has later been extended to the mesoscopic description of polymers 23 and, more in general, of rigid moieties in larger molecules.…”

Section: Introductionmentioning

confidence: 99%

Molecular Graphics of Convex Body Fluids

Gabriel

Meyer

Germano

2008

J. Chem. Theory Comput.

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Coarse-grained modeling of molecular fluids is often based on nonspherical convex rigid bodies like ellipsoids or spherocylinders representing rodlike or platelike molecules or groups of atoms, with site-site interaction potentials depending both on the distance among the particles and the relative orientation. In this category of potentials, the Gay-Berne family has been studied most extensively. However, conventional molecular graphics programs are not designed to visualize such objects. Usually the basic units are atoms displayed as spheres or as vertices in a graph. Atomic aggregates can be highlighted through an increasing amount of stylized representations, e.g., Richardson ribbon diagrams for the secondary structure of proteins, Connolly molecular surfaces, density maps, etc., but ellipsoids and spherocylinders are generally missing, especially as elementary simulation units. We fill this gap providing and discussing a customized OpenGL-based program for the interactive, rendered representation of large ensembles of convex bodies, useful especially in liquid crystal research. We pay particular attention to the performance issues for typical system sizes in this field. The code is distributed as open source.

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Section: Introductionmentioning

confidence: 99%

Molecular Graphics of Convex Body Fluids

Gabriel

Meyer

Germano

2008

J. Chem. Theory Comput.

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“…[8,9] This material interest merges with its inherent biological interest in the currently pursued attempt to employ DNA, perhaps the most emblematic of all helical biomolecular systems, as a building-block for new materials. [10,11] Rather surprisingly, in spite of this wealth of inspiration sources, helices appear to have been mostly overlooked in past theoretical studies on hard-body non-spherical particle systems, focussing mostly on rod-or disc-like particles, [12,13] possibly due to the tacit assumption that helices, as elongated objects, can be assimilated to rods.…”

Section: Introductionmentioning

confidence: 99%

Self-assembly of hard helices: a rich and unconventional polymorphism

et al. 2014

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Hard helices can be regarded as a paradigmatic elementary model for a number of natural and synthetic soft matter systems, all featuring the helix as their basic structural unit: from natural polynucleotides and polypeptides to synthetic helical polymers; from bacterial flagella to colloidal helices. Here we present an extensive investigation of the phase diagram of hard helices using a variety of methods. Isobaric Monte Carlo numerical simulations are used to trace the phase diagram: on going from the low-density isotropic to the high-density compact phases, a rich polymorphism is observed exhibiting a special chiral screw-like nematic phase and a number of chiral and/or polar smectic phases. We present a full characterization of the latter, showing that they have unconventional features, ascribable to the helical shape of the constituent particles. Equal area construction is used to locate the isotropic-to-nematic phase transition, and results are compared with those stemming from an Onsager-like theory. Density functional theory is also used to study the nematic-to-screw-nematic phase transition: within the simplifying assumption of perfectly parallel helices, we compare different levels of approximation, that is second-and third-virial expansions and Parsons-Lee correction.arXiv:1408.1199v1 [cond-mat.soft] 6 Aug 2014 2

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“…Hard non-spherical particles are often taken as 'zeroth-order' models for lyotropic or colloidal LCs in which the appearance of anisotropic phases is controlled by the solute concentration. 49,50 Impressively, the theoretical treatment of hard non-spherical fluids dates back to the 1940s: in his pioneering work on nematic LCs, Onsager 51,52 proposed the now well-accepted free-energy functional for the nematic state and demonstrated that when only athermal (excluded-volume) contributions are taken into account, the isotropic-nematic phase transition can be driven by entropy alone. Onsager's original second-order virial theory was extended by Parsons 53 and by Lee 54,55 (PL) to incorporate the contributions from the higher-order terms based on those of a reference hard-sphere system.…”

Section: Introductionmentioning

confidence: 99%

Understanding and Describing the Liquid-Crystalline States of Polypeptide Solutions: A Coarse-Grained Model of PBLG in DMF

Müller

Jackson

2014

Macromolecules

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A perturbation theory is employed to construct a free-energy functional capable of describing the isotropic and nematic phases of attractive rod-like particles. An algebraic van der Waals-Onsager equation of state is then developed to determine the global phase behaviour of prolate particles for various aspect ratios and strengths of the attractive potential. Compared with the phase diagram of their athermal analogues, the incorporation of an attractive potential is seen to stabilize the nematic state leading to an increase in the degree of orientational order of the system at high densities. The most salient feature of these fluids is the existence of regions of nematic-nematic phase separation. The simple model is used to describe the phase behaviour of solutions of a relatively rigid polypeptide, poly-(γ -benzyl-L-glutamate) (PBLG), in dimethylformamide (DMF); this system exhibits a unique phase separation between two liquidcrystalline states. The coarse-grained representation of the mesogen employed herein * To whom correspondence should be addressed 1 is a hard spherocylinder decorated with an attractive square-well potential which acts at the center of mass of the particle. A quantitative description of the experimental isotropic-nematic phase behaviour of the PBLG solutions can be achieved from the proposed model with the use of just two temperature-dependent parameters.

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Hard Convex Body Fluids

Cited by 251 publications

References 258 publications

Molecular Graphics of Convex Body Fluids

Molecular Graphics of Convex Body Fluids

Self-assembly of hard helices: a rich and unconventional polymorphism

Understanding and Describing the Liquid-Crystalline States of Polypeptide Solutions: A Coarse-Grained Model of PBLG in DMF

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