The temperature dependence of the heat conductivity of a liquid crystal studied by molecular dynamics simulation

Sarman, Sten; Laaksonen, Aatto

doi:10.1016/j.cplett.2009.11.073

Cited by 9 publications

(10 citation statements)

References 18 publications

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“…The component parallel to the cholesteric axis decays monotonously to zero and it is similar to the corresponding heat current correlation function in the achiral nematic phase. 38 The component perpendicular to the cholesteric axis falls off and becomes negative before the final decay to zero, which is also the case in the achiral nematic phase. In Fig.…”

Section: Calculations Results and Discussionmentioning

confidence: 76%

“…We obtain a heat conductivity of about 2.77 which is about the same as the heat conductivity of the corresponding nematic liquid crystal that is obtained when the chiral parameter is equal to zero. 38 The Leslie coefficient n is equal to about 0.012. This is about two orders of magnitude lower than the heat conductivity and ten times lower than the value of the Leslie coefficient that was found for the twisted strings of discotic ellipsoids in the previous studies 15,16 and therefore considerably longer simulation run lengths, i.e.…”

Section: Calculations Results and Discussionmentioning

confidence: 99%

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Thermomechanical coupling, heat conduction and director rotation in cholesteric liquid crystals studied by molecular dynamics simulation

Sarman

Laaksonen

2013

Phys. Chem. Chem. Phys.

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The lack of a centre of inversion in a cholesteric liquid crystal allows linear cross couplings between thermodynamic forces and fluxes that are polar vectors and pseudovectors, respectively. This makes it possible for a temperature gradient parallel to the cholesteric axis to induce a torque that rotates the director, a phenomenon known as the Lehmann effect or thermomechanical coupling. The converse is also possible: a torque applied parallel to the cholesteric axis rotates the director and drives a heat flow. In order to study this phenomenon, nonequilibrium molecular dynamics simulation algorithms and Green-Kubo relations evaluated by equilibrium molecular dynamics simulation have been used to calculate the Leslie coefficient, i.e. the cross coupling coefficient between the temperature gradient and the director angular velocity, for a model system composed of soft prolate ellipsoids of revolution interacting via the Gay-Berne potential augmented by a chiral interaction potential causing the formation of a cholesteric phase. It is found that the Leslie coefficient is two orders of magnitudes smaller than other transport coefficients such as the heat conductivity and the twist viscosity, so that very long simulations are required to evaluate it. The Leslie coefficient decreases with the pitch but it has not been possible to determine the exact functional dependence of this coefficient on the pitch. Since very long simulations have been performed to evaluate the Leslie coefficient, very accurate values have been obtained for the twist viscosity and the heat conductivity as a by-product and it is found that they are very similar to the values of the corresponding quantities in the achiral nematic phase that arises when the pitch goes to infinity.

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Section: Calculations Results and Discussionmentioning

confidence: 76%

Section: Calculations Results and Discussionmentioning

confidence: 99%

Thermomechanical coupling, heat conduction and director rotation in cholesteric liquid crystals studied by molecular dynamics simulation

Sarman

Laaksonen

2013

Phys. Chem. Chem. Phys.

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“…Moreover, this is also helpful to achieve a good model of molecular interactions that provides valuable information about the structure of the phases formed and their transitions. In view of the practical difficulties and the increasing importance of predicting the properties of target molecular materials, it is of substantial significance to use statistical simulations for the calculation of physical properties [7][8][9]. It involves not only the precise method of obtaining the information on physical properties from a given electronic configuration but also resolving the probability of conformers (configurations) used as a statistical weighting for the molecules because most of the LC molecules are found to have a number of conformations at room temperature.…”

Section: Introductionmentioning

confidence: 99%

Molecular Structure and Conformational Behavior of a Nematogen—A Statistical Approach

Praveen¹,

Ojha²

2011

Molecular Crystals and Liquid Crystals

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Molecular structure and conformational behavior of a nematogen p-ethoxy salicylidene-n-butyl aniline (ESBA) has been studied with respect to translational and orientational motions. The atomic net charge and dipole moment components at each atomic center have been evaluated using the complete neglect differential overlap (CNDO=2) method. The modified Rayleigh-Schrodinger perturbation theory along with multicentered-multipole expansion method has been employed to evaluate the longrange intermolecular interactions, and a 6-exp potential function has been assumed for short-range interactions. The interaction energy values obtained during the different modes of molecular interactions have been taken as input to calculate the configurational probability at room temperature (300 K). On the basis of stacking, in-plane, and terminal interaction energy calculations, all possible geometrical arrangements between the molecular pairs have been considered. The effect of nonmesogenic and noninteracting solvent (benzene) has also been studied. Further, the analysis of conformational behavior provides valuable information on configurational freedom of a molecule that may be useful in understanding the structure of phases and their transitions.

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“…LC phases are characterized by a long-range orientational order and a partial or complete positional disorder responsible for the flow properties. The vast interest in these molecular materials can be partly ascribed to the scores of technical applications, as well as to obtain a fundamental understanding of physicochemical aspects of the model systems that exhibit/cause liquid crystallinity [1,2]. The phase transitions occur in LC materials based on their intrinsic properties, which are characterized by the arrangement of the molecules, the conformation of the molecules, and intermolecular interactions [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic Stability of the Nematic Phase and Configurational Entropy of Mesogens: A Molecular Simulation Approach

Praveen¹,

Ojha²

2011

Molecular Crystals and Liquid Crystals

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The thermodynamic stability of the nematic phase and the configurational entropy of mesogens-p-n-pentylbenzoic acid (5BAC) and p-n-hexylbenzoic acid (6BAC)-have been studied. The atomic net charge and dipole moment components at each atomic center have been evaluated using the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh-Schrodinger perturbation theory along with multicenteredmultipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a "6-exp" potential function has been assumed for short-range interactions. The interaction energy values obtained with respect to translational and orientational motions during the different modes of molecular interactions have been taken as input to estimate the configurational entropy and Helmholtz free energy at room temperature, nematic-isotropic transition temperature, and above transition temperature. The observed difference in free energy of the molecules between the mesophase and the crystal phase during in-plane interactions suggests the thermodynamic stability of the nematic phase. Further, the comparable values of translational entropy during stacking and in-plane interactions are helpful to understand the relative flexibility/stability of one configuration over the other.

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The temperature dependence of the heat conductivity of a liquid crystal studied by molecular dynamics simulation

Cited by 9 publications

References 18 publications

Thermomechanical coupling, heat conduction and director rotation in cholesteric liquid crystals studied by molecular dynamics simulation

Thermomechanical coupling, heat conduction and director rotation in cholesteric liquid crystals studied by molecular dynamics simulation

Molecular Structure and Conformational Behavior of a Nematogen—A Statistical Approach

Thermodynamic Stability of the Nematic Phase and Configurational Entropy of Mesogens: A Molecular Simulation Approach

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