Thermodynamical scaling of the low frequency relaxation time in liquid crystalline phases

Urban, S.; Würflinger, A.

doi:10.1103/physreve.72.021707

Cited by 34 publications

(40 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This result is consistent with the magnitude of the scaling exponent, γ ) 5, which is larger than those obtained for similar nematogenic nPCH compounds (having the CN group instead of NCS). 9 On the other hand, potential barriers for nPCHs 30 are close to the value for 6CHBT. The γ for 6CHBT is also large in comparison to alkylisothiocyanato-biphenyl liquid crystals, for which γ is in the range 2-3.…”

Section: Resultsmentioning

confidence: 61%

“…Measurement of τ | as functions of temperature T, pressure P, and specific volume V (inverse of mass density) is essential to understanding the nature of the molecular interactions in LC phases. 3,[6][7][8][9][10][11] In particular, the effective steepness of the interaction potential in the LC phase can be determined from analysis of τ | at different thermodynamic conditions. Since mesogenic materials have appreciable dipole moments (anisotropic interactions being the origin of the liquid crystallinity), dielectric spectroscopy is an especially effective technique for such experiments.…”

Section: Introductionmentioning

confidence: 99%

“…20 Equation 2 was recently applied to the longitudinal relaxation times of several LC substances measured under different thermodynamic conditions. [9][10][11] For LC the superposition of τ | is very accurate, with f assuming a simple exponential form…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Interaction Potential in Nematogenic 6CHBT

et al. 2008

View full text Add to dashboard Cite

Pressure-volume-temperature (PVT) measurements were carried out on the nematic liquid crystal 4(trans-4′-n-hexylcyclohexyl)isothiocyanatobenzene (6CHBT). In combination with previous dielectric relaxation measurements at elevated pressure and new measurements extending to GHz frequencies, the characteristics of the anisotropic interaction potential were determined. The thermodynamic potential parameter, Γ, which measures the variation of the interaction energy with volume, equals 5.03 ( 0.06, with a barrier height equal to ∼7 kJ/mol. Thus, there is a low potential barrier to reorientations of the 6CHBT molecule about its short axis; however, the retarding potential is strongly volume-dependent. The longitudinal reorientational times determined for various thermodynamic conditions superpose using a scaling exponent equal to Γ within the experimental error. It then follows, as found recently for other liquid crystals, that this relaxation time must be constant along the pressure-dependent clearing line. Thus, the control parameter (e.g., Gibbs free energy) governing the competition between the anisotropic energy and the entropy must also govern the rotational dynamics in the ordered phase of this liquid crystal.

show abstract

Section: Resultsmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Interaction Potential in Nematogenic 6CHBT

et al. 2008

View full text Add to dashboard Cite

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

“…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%

Volumetric study ofn-octyloxy-cyanobiphenyl (8OCB)

et al. 2013

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Thermodynamical scaling of the low frequency relaxation time in liquid crystalline phases

Cited by 34 publications

References 29 publications

Interaction Potential in Nematogenic 6CHBT

Interaction Potential in Nematogenic 6CHBT

Scaling of the dynamics of flexible Lennard-Jones chains

Volumetric study ofn-octyloxy-cyanobiphenyl (8OCB)

Contact Info

Product

Resources

About