Monte Carlo simulations of zero electric field gradient liquid crystal mixtures

Burnell, E. Elliott; Berardi, Roberto; Syvitski, Raymond T.; Zannoni, Claudio

doi:10.1016/s0009-2614(00)01178-7

Cited by 19 publications

(12 citation statements)

References 14 publications

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“…We described the solute as a spherocylinder having the same dimensions (radius 2.5 Å and length 5.0 Å) while we referred to ref. 38 to describe the rod fluid, using spherocylinders of radius r = 2.5 Å and length l = 10.0 Å and a number density ρ = 0.0024 Å −3 . Differences of G cav have been calculated for the solute oriented along the nematic director (Δ G ‖ ) and the solute perpendicular to the director (Δ G ⟂ ), determined both in a perfectly aligned nematic solvent (order parameter S = 1.0) and in a partially ordered fluid, having S = 0.7.…”

Section: Resultsmentioning

confidence: 99%

Building cavities in a fluid of spherical or rod‐like particles: A contribution to the solvation free energy in isotropic and anisotropic polarizable continuum model

Benzi¹,

Cossi²,

Improta

et al. 2005

J Comput Chem

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A general formalism for the calculation of cavitation energies in the framework of the scaled particle theory has been implemented in the Polarizable Continuum Model (PCM), contributing to the nonelectrostatic part of the molecular free energy in solution. The solute cavity and the solvent molecules are described as hard spherocylinders, whose radius and length are related to the actual molecular shape, while the solvent density is estimated from experimental data, or from the solvent molecular volume, suitably scaled. The present model can describe isotropic solutions of spherical and rod-like molecules in spherical or rod-like solvents, and also anisotropic solutions in which the solvent molecules are oriented in space: in this case, the cavitation energy also depends on the relative orientation of solute and solvent molecules. Test calculations have been performed on simple systems to evaluate the accuracy of the present approach, in comparison with other methods and with the available experimental estimates of the cavitation energy, giving encouraging results.

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Section: Resultsmentioning

confidence: 99%

Building cavities in a fluid of spherical or rod‐like particles: A contribution to the solvation free energy in isotropic and anisotropic polarizable continuum model

Benzi¹,

Cossi²,

Improta

et al. 2005

J Comput Chem

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“…Finally, our analysis shows that the practice of treating electrostatic interactions within uniaxial continuum descriptions of the solvent with empirically derived approximations for the solvent-solute potential is too simplistic. Moreover, even if the concept of an ''average electric field gradient'' 10,14 characteristic of each nematic solvent and its putative influence on solute quadrupole moments is viewed in its most primitive role-as a coarse descriptor of the nematic mean fieldthose critical experimental probes of evidence for such an average field gradient 31 and the results from theory 11 and from computer simulations 30 indicate that the concept is flawed. phenylacetylene ͑4a͒ and 4-n-pentyloxyphenylacetylene ͑4b͒ were obtained in excellent yields by coupling of the appropriate aryl halide ͑2a or 2b͒ with ͑trimethylsilyl͒acetylene in the presence of a palladium catalyst.…”

Section: Discussionmentioning

confidence: 99%

“…This picture was soon demonstrated to be inadequate 17,18 and it is now well established by several theoretical works and numerous computer simulations [19][20][21][22][23] that residual dipolar interactions are not only present in apolar mesophases, nematic, smectic or columnar, but that they can also have substantial effects on the thermodynamic stability of these phases, 24 produce molecular dimerisation via dipolar association, 25,26 give rise to phase re-entrance phenomena, 27 cause structural modifications in smectics, 28,29 etc. On the other hand, it was demonstrated theoretically, 11 and later found in simulations, 30 that the ad hoc ''EFG of the solvent'' is not strictly a solvent property but depends on the structure of the solute molecules as well. Moreover, the notion of a solvent-characteristic EFG is proven inadequate to account for direct NMR measurements of average EFGs experienced by the quadrupolar nuclei of the noble gas isotopes 21 Ne, 83 Kr, and 131 Xe in nematic solvents.…”

Section: Introductionmentioning

confidence: 99%

Ordering of apolar and polar solutes in nematic solvents

Dingemans

Photinos

Samulski

et al. 2003

The Journal of Chemical Physics

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The quadrupolar splittings of deuteriated para-and ortho-dichlorobenzene ͑1,4-DCB and 1,2-DCB, respectively͒ are measured by nuclear magnetic resonance ͑NMR͒ in the nematic solvents hexyland pentyloxy-substituted diphenyl diacetylene ͑DPDA-C6 and DPDA-OC5, respectively͒. Measurements are taken for all four combinations of the nominally apolar ͑1,4-DCB͒ and polar ͑1,2-DCB͒ solutes in the apolar ͑DPDA-C6͒ and polar ͑DPDA-OC5͒ solvents, and throughout the entire nematic temperature range of the solutions. The temperature dependence of the second-rank orientational order parameters of the solutes are obtained from these measurements and the respective order parameters of the mesogenic cores of solvent molecules are obtained independently from carbon-13 NMR measurements. The order parameter profiles of the two solutes are found to be very different but show little variation from one solvent to the other. The results are analyzed and interpreted in terms of the underlying molecular interactions using atomistic solvent-solute potentials. The influence of electrostatic interactions on solute ordering is directly evaluated by computing the order parameters with and without the electrostatic component of the atomistic potential. It is observed to be small. It is also found that the important interactions in these solventsolute systems are operative over short intermolecular distances for which the representation of the partial charge distributions in terms of overall molecular dipole and quadrupole moments is not valid.

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“…28,29 In addition, others have emphasized that the efg experienced by a solute should be a property of both the solute and the liquid-crystal solvent. 10,15,22 In the following paper 47 we report results from Monte Carlo simulations of the experimental results reported in this paper.…”

Section: Resultsmentioning

confidence: 99%

“…The poorer quality of fits obtained for the component liquid-crystal solvents, as well as the change in the magnitude ͑not sign͒ of efg values compared to those obtained from D 2 experiments, is consistent with other studies which conclude that the average efg experienced by a solute is a function of both the solute and the solvent and therefore is not a property of the liquid-crystal solvent alone. 10,15,22,28,29 We emphasize the important point: the orientational order of solutes in MMs can be predicted to about 10% using models for short-range interactions that depend on the solute size and shape-other longer-range electrostatic interactions appear to be unimportant in these MMs. In other liquidcrystal solvents, additional electrostatic interactions ͑such as that between the mean electric field squared and the molecular polarizability anisotropy or the efg-Q mol interaction͒ play a role.…”

Section: Introductionmentioning

confidence: 92%

Orientational order of near D3h solutes in nematic liquid crystals

Danilovič

Burnell

2009

The Journal of Chemical Physics

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Solutes that are similar in size, have a shape that is close to D(3h) symmetry but contain dissimilar substituent groups (methyl versus chloro, contributing different electrostatic interactions to the anisotropic intermolecular potential), are used to delineate the short- and long-range anisotropic intermolecular interactions that lead to solute orientational order in nematic liquid crystals. The short-range interactions should be similar for all solutes and for D(3h) symmetry should yield a single independent order parameter, whereas the long-range interactions are expected to differ with solute. Short-range size and shape mechanisms account for solute orientational order measured in magic mixtures (e.g., 55 wt % ZLI-1132/N-p-ethoxybenzylidene-p(')-n-butylaniline), whereas additional mechanisms are required in other nematic liquid-crystal solvents. The results obtained for long-range interactions cannot be rationalized in detail using simple mean-field models that incorporate solute dipoles, quadrupoles, or polarizabilities. The results suggest that details of the solute electrostatics may need to be incorporated into the description of the anisotropic intermolecular potential.

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Monte Carlo simulations of zero electric field gradient liquid crystal mixtures

Cited by 19 publications

References 14 publications

Building cavities in a fluid of spherical or rod‐like particles: A contribution to the solvation free energy in isotropic and anisotropic polarizable continuum model

Building cavities in a fluid of spherical or rod‐like particles: A contribution to the solvation free energy in isotropic and anisotropic polarizable continuum model

Ordering of apolar and polar solutes in nematic solvents

Orientational order of near D3h solutes in nematic liquid crystals

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