Low frequency relaxation in liquid crystals in relation to structural relaxation in glass-formers

Urban, S.; Roland, C. M.

doi:10.1016/j.jnoncrysol.2010.05.093

Cited by 34 publications

(45 citation statements)

References 57 publications

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“…We refer to this scaling as power-law * a.a.veldhorst@gmail.com † tbs@ruc.dk density scaling. To date, many more molecular liquids have been shown to obey power-law density scaling to a good approximation, including polymers, but also ionic liquids [16][17][18][19][20][21][22] and liquid crystals [23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Scaling of the dynamics of flexible Lennard-Jones chains

Veldhorst

Dyre

Schrøder

2014

The Journal of Chemical Physics

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The isomorph theory provides an explanation for the so-called power law density scaling which has been observed in many molecular and polymeric glass formers, both experimentally and in simulations. Power law density scaling (relaxation times and transport coefficients being functions of ρ γ S /T , where ρ is density, T is temperature, and γS is a material specific scaling exponent) is an approximation to a more general scaling predicted by the isomorph theory. Furthermore, the isomorph theory provides an explanation for Rosenfeld scaling (relaxation times and transport coefficients being functions of excess entropy) which has been observed in simulations of both molecular and polymeric systems. Doing molecular dynamics simulations of flexible Lennard-Jones chains (LJC) with rigid bonds, we here provide the first detailed test of the isomorph theory applied to flexible chain molecules. We confirm the existence of isomorphs, which are curves in the phase diagram along which the dynamics is invariant in the appropriate reduced units. This holds not only for the relaxation times but also for the full time dependence of the dynamics, including chain specific dynamics such as the end-to-end vector autocorrelation function and the relaxation of the Rouse modes. As predicted by the isomorph theory, jumps between different state points on the same isomorph happen instantaneously without any slow relaxation. Since the LJC is a simple coarse-grained model for alkanes and polymers, our results provide a possible explanation for why power-law density scaling is observed experimentally in alkanes and many polymeric systems. The theory provides an independent method of determining the scaling exponent, which is usually treated as a empirical scaling parameter.

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Section: Introductionmentioning

confidence: 99%

Scaling of the dynamics of flexible Lennard-Jones chains

Veldhorst

Dyre

Schrøder

2014

The Journal of Chemical Physics

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“…This is seen in studies of calamitic liquid crystals (LCs) using hydrostatic pressure, which number in the hundreds (for reviews see [1][2][3][4][5][6][7]). From PVT data combined with dielectric relaxation times measured in various LC phases, the phase behaviour, nematic order parameter, and the dielectric tensor permittivity components of nematics have been determined.…”

Section: Introductionmentioning

confidence: 99%

“…Dynamical quantities (relaxation time τ , viscosity, diffusion constant, etc.) have been reported for isobaric, isochoric, and isothermal conditions [2,3,[5][6][7], enabling determination, via the thermodynamic scaling…”

Section: Introductionmentioning

confidence: 99%

“…Email: ufurban@cyf-kr.edu.pl of the interaction parameter γ characterising the steepness of the intermolecular potential [5][6][7][8][9][10][11][12]. The possible equivalence of the two potential parameters, Γ and γ , was discussed in refs.…”

Section: Introductionmentioning

confidence: 99%

“…The possible equivalence of the two potential parameters, Γ and γ , was discussed in refs. [5][6][7]13]. n-Octyloxy-cyanobiphenyl (8OCB, molar mass = 307.4 g/mol), CN H 17 C 8 O exhibits isotropic (I), nematic (N), smectic A d (S Ad ), and crystalline (Cr) phases, as revealed by numerous studies performed at ambient pressure (for example [14,15]), as well as at elevated pressure [16][17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

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Volumetric study ofn-octyloxy-cyanobiphenyl (8OCB)

et al. 2013

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Volumetric measurements were carried out on n-octyloxy-cyanobiphenyl (8OCB) over temperatures from ambient to 150• C at pressures up to 200 MPa, encompassing the liquid, nematic and smectic liquid crystalline, and crystal states. From the step changes in volume at the transitions, the phase boundaries and the associated activation enthalpies and energies were determined. The results are consistent with prior studies that were limited to a narrower range of thermodynamic conditions. The thermodynamic potential parameter, Γ , found for the isotropic-nematic transition, =3.15, is significantly smaller than the scaling exponent γ (=4.4) that superposes the longitudinal relaxation times in the nematic state. From this non-equivalence, we conclude that the order parameter must vary with pressure along the clearing line. By comparing the phase behaviour of the nematic state for isochoric and isobaric conditions, the relative contribution of volume was determined to be less that the effect of thermal energy on the thermodynamic stability.

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High‐Pressure Investigations of Liquid Crystals

Urban

2014

Handbook of Liquid Crystals

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Low frequency relaxation in liquid crystals in relation to structural relaxation in glass-formers

Cited by 34 publications

References 57 publications

Scaling of the dynamics of flexible Lennard-Jones chains

Scaling of the dynamics of flexible Lennard-Jones chains

Volumetric study ofn-octyloxy-cyanobiphenyl (8OCB)

High‐Pressure Investigations of Liquid Crystals

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