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

Wu, Liang; Müller, Erich A.; Jackson, George

doi:10.1021/ma401230x

Cited by 18 publications

(34 citation statements)

References 144 publications

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“…As a consequence, the usual van derWaals “vapour-liquid” phase transition is now exhibited in the anisotropic region of the phase diagram, corresponding to nematic-nematic coexistence with its associated critical point. A similar progression from V-L-N, through I-N, to I-N 1 -N 2 phase behaviour with increasing aspect ratio has been observed for attractive rod-like LC molecules [77,93–98]. The coexistence between two nematic phases has been found experimentally in studies of hexa-alkylbenzene derivatives of discotic mesogens [99] and in solutions of the calamitic polypeptides [95], both of which are characterized by extreme oblate and prolate aspect ratios.…”

Section: Resultssupporting

confidence: 65%

“…We are therefore confident that, qualitatively, at least, our model will describe the isotropic and nematic ordering behaviour of discotic thermotropic mesogens. A simple square-well hard-spherocylinder model of this generic form has been used to successfully represent the ordering behaviour of solutions of rod-like polypeptide (poly γ -benzyl L-glutamate) macromolecules with a quantitative description of the phase boundaries [98]. …”

Section: Discussionmentioning

confidence: 99%

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Liquid Crystal Phase Behaviour of Attractive Disc-Like Particles

Jackson

Müller

2013

IJMS

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We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic) of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids.

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Section: Resultssupporting

confidence: 65%

Section: Discussionmentioning

confidence: 99%

Liquid Crystal Phase Behaviour of Attractive Disc-Like Particles

Jackson

Müller

2013

IJMS

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“…Simulations based on coarse-grained models can access longer time and length scales than their atomistic counterparts, allowing a bulk description of fluids. Coarse-grained models are commonly used to represent a simplified picture of large molecules, such as biomolecules [12][13][14][15][16], polymers [17][18][19][20][21][22], or liquid crystals [23][24][25][26][27][28]. Moreover, simulation results obtained from coarse-grained models can be directly compared with theoretical predictions that are based on a well-defined Hamiltonian, such as the family of perturbation theories developed from the statistical association fluid theory (SAFT) [29][30][31][32][33][34][35][36].…”

Section: Introductionmentioning

confidence: 99%

“…Other more elaborated interaction models have been proposed, e.g. hard-spherocylinder with an attractive square-well potential [28,[62][63][64], hard-disc with an anisotropic square-well attractive potential [27], hard-spherocylinder with an attractive Lennard-Jones potential [65], anisotropic soft-core spherocylinder potential [66,67], and copolymers [68][69][70]. In this work, we focus our study on the isotropic-nematic phase behaviour of linear and partially-flexible Lennard-Jones chain fluids.…”

Section: Introductionmentioning

confidence: 99%

Liquid-crystal phase equilibria of Lennard-Jones chains

2016

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Liquid-crystal phase equilibria of Lennard-Jones chain fluids and the solubility of a Lennard-Jones gas in the coexisting phases are calculated from Monte Carlo simulations. Direct phase equilibria calculations are performed using an expanded formulation of the Gibbs ensemble. Monomer densities, order parameters, and equilibrium pressures are reported for the coexisting isotropic and nematic phases of: (1) linear Lennard-Jones chains, (2) a partially-flexible Lennard-Jones chain, and (3) a binary mixture of linear Lennard-Jones chains. The effect of chain length is determined by calculating the isotropic-nematic coexistence of linear Lennard-Jones chain fluids made of 8, 10, and 12 segments (8-, 10-, 12-mer). The effect of molecular flexibility on the isotropic-nematic equilibrium is studied for a Lennard-Jones 10-mer chain fluid with one freely-jointed segment at the end of the chain. An isotropic-nematic phase split and fractionation are reported for a binary mixture of linear 7-mer and 12-mer chains. Simulation results are compared with theoretical results as obtained from a recently developed analytical equation of state based on perturbation theory. Excellent agreement between theory and simulations is observed. The solubility of a monomer Lennard-Jones gas in the coexisting isotropic and nematic phases is estimated using the Widom test-particle insertion method. A linear relationship between solubility difference and density difference at isotropic-nematic coexistence is observed. It is shown that gas solubility is independent of the nematic ordering of the fluid, at constant temperature and density conditions.

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“…In this approach, the orientationally dependent attractive interactions are considered as the key to the orientational order in thermotropic liquid crystals controlled by the temperature. In many cases, anisotropic fluids exhibit simultaneously lyotropic and thermotropic behaviour, which can be presented in concentration-temperature phase diagrams [15,25]. Due to this, both repulsive and attractive interactions between particles should be taken into account.…”

mentioning

confidence: 99%

On generalization of Van der Waals approach for isotropic-nematic fluid phase equilibria of anisotropic fluids in disordered porous medium

Holovko¹,

Shmotolokha²

2020

Condens. Matter Phys.

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A generalized Van der Waals approach is developed for anisotropic fluids in disordered porous media. As the reference system a hard spherocylinder fluid in a disordered porous medium is considered and described in the framework of the scaled particle theory with the Carnahan-Starling and Parsons-Lee corrections. The attractive part of interaction is treated in the framework of the mean field approximation in which due to orientational dependence of the excluded volume of two spherocylinders, a coupling between attractive and repulsive contributions is found. We focus on spherocylinder fluids with sufficiently long particle lengths for which the nematicnematic transition was established. It is shown that these two nematic phases have different densities and are characterized by different orientational ordering. Strong influence of the type of interparticle attraction on the phase behaviour of anisotropic fluids in disordered porous media is established. Three simple models for this purpose are considered, namely a model with the Lennard-Jones anisotropic attraction, a model with modified Lennard-Jones attraction and a model with anisotropic square-well potential. For all considered models, the phase diagram shifts to the region of lower densities and lower temperatures as the porosity decreases.cylinders when the length of a spherocylinder L 1 → ∞ and the diameter D 1 → 0 in such a way that the non-dimensional concentration C 1 = πρ 1 L 2 1 D 1 /4 is fixed, where ρ 1 = N 1 /V, N 1 is the number of spherocylinders, V is the volume of the system [16]. The application of the scaled particle theory (SPT) previously developed for a hard-sphere fluid [18,19] provides an efficient way to incorporate higher order contributions neglected in the Onsager theory [20][21][22].Another mechanism of formation of liquid crystalline matter can be connected with anisotropic attraction usually treated in molecular mean-field approaches such as the Maier-Saupe theory [23,24]. In this approach, the orientationally dependent attractive interactions are considered as the key to the orientational order in thermotropic liquid crystals controlled by the temperature. In many cases, anisotropic fluids exhibit simultaneously lyotropic and thermotropic behaviour, which can be presented in concentration-temperature phase diagrams [15,25]. Due to this, both repulsive and attractive interactions between particles should be taken into account. This leads to the Van der Waals picture of fluids [26] in which the hard molecular core is treated as the reference system that determines the fluid structure while the attractions are incorporated by the perturbation way [27][28][29]. The generalized Van der Waals theory for anisotropic fluids was formulated by Cotter [30][31][32] and by the Gelbart group [33,34]. By combining the Onsager theory with the Van der Waals approach in the group of Jackson [15,25] for the attractive hard spherocylinders, four possible pairs of coexisting fluid phases were predicted, namely vapor-liquid, vapor-nematic, liquid-nemat...

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

Cited by 18 publications

References 144 publications

Liquid Crystal Phase Behaviour of Attractive Disc-Like Particles

Liquid Crystal Phase Behaviour of Attractive Disc-Like Particles

Liquid-crystal phase equilibria of Lennard-Jones chains

On generalization of Van der Waals approach for isotropic-nematic fluid phase equilibria of anisotropic fluids in disordered porous medium

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