High‐Pressure Investigations of Liquid Crystals

Urban, S.

doi:10.1002/9783527671403.hlc036

Cited by 5 publications

(15 citation statements)

References 133 publications

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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%

“…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%

“…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%

“…With these in mind, we decided to perform PVT measurements over broad temperature and pressure ranges, to allow us to analyse the dielectric relaxation times obtained by the Bochum group [20,21]. Our aim is to apply thermodynamic scaling of the relaxation times, Equation (2), in order to determine the interaction parameter characterising the steepness of the interaction potential ( [5][6][7]23] and references therein).…”

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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Volumetric study ofn-octyloxy-cyanobiphenyl (8OCB)

et al. 2013

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Activation volume of selected liquid crystals in the density scaling regime

Grzybowski

Urban

Mróz

et al. 2017

Sci Rep

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In this paper, we demonstrate and thoroughly analyze the activation volumetric properties of selected liquid crystals in the nematic and crystalline E phases in comparison with those reported for glass-forming liquids. In the analysis, we have employed and evaluated two entropic models (based on either total or configurational entropies) to describe the longitudinal relaxation times of the liquid crystals in the density scaling regime. In this study, we have also exploited two equations of state: volumetric and activation volumetric ones. As a result, we have established that the activation volumetric properties of the selected liquid crystals are quite opposite to such typical properties of glass-forming materials, i.e., the activation volume decreases and the isothermal bulk modulus increases when a liquid crystal is isothermally compressed. Using the model based on the configurational entropy, we suggest that the increasing pressure dependences of the activation volume in isothermal conditions and the negative curvature of the pressure dependences of isothermal longitudinal relaxation times can be related to the formation of antiparallel doublets in the examined liquid crystals. A similar pressure effect on relaxation dynamics may be also observed for other material groups in case of systems, the molecules of which form some supramolecular structures.

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Insight from high-pressure dielectric studies into molecular dynamics of the itraconazole-glycerol mixture in smectic and isotropic phases

Rams-Baron

Musiał

Kramarczyk

et al. 2022

The Journal of Chemical Physics

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We present here the results of high-pressure broadband dielectric spectroscopy (BDS) measurements for a mixture of liquid-crystalline drug itraconazole (ITZ) and glycerol (GLY) at a critical concentration of 5% w/w in which the nematic order is eliminated. In the investigated system, smectic-A to isotropic phase transition leaves a clear fingerprint on the dielectric response allowing a phase diagram creation using BDS data. By following the α-relaxation dynamics under different thermodynamic conditions, we provide insight into the effect of pressure on temperature and the phenomenology of the smectic-A to the isotropic phase transition. Additional measurements of specific volume as a function of pressure and temperature provide us with deeper insight into material properties that could be analyzed comprehensively via the equation of state. We proved the validity of the density scaling concept showing that the mixture's complexity does not exclude thermodynamic scaling of dynamic properties related to the α-process in the smectic-A phase. The low value of scaling exponent γ = 2.00 {plus minus} 0.02 and a high ratio of the activation energy at constant volume, EV, to the activation enthalpy at constant pressure, HP, indicate that temperature is a dominant variable controlling α-relaxation dynamics in the ordered smectic-A phase of ITZ-GLY mixture.

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High‐Pressure Investigations of Liquid Crystals

Cited by 5 publications

References 133 publications

Volumetric study ofn-octyloxy-cyanobiphenyl (8OCB)

Volumetric study ofn-octyloxy-cyanobiphenyl (8OCB)

Activation volume of selected liquid crystals in the density scaling regime

Insight from high-pressure dielectric studies into molecular dynamics of the itraconazole-glycerol mixture in smectic and isotropic phases

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