An intriguing problem in condensed matter physics is understanding the glass transition, in particular the dynamics in the equilibrium liquid close to vitrification Recent advances have been made by using hydrostatic pressure as an experimental variable These results are reviewed, with an emphasis in the insight provided into the mechanisms underlying the relaxation properties of glass-forming liquids and polymers

https://iopscience.iop.org/article/10.1088/0034-4885/68/6/R03/pdf

Supercooled dynamics of glass-forming liquids and polymers under hydrostatic pressure

Phase transitions in liquid crystals

High-pressure fluid-phase equilibria: Experimental methods and systems investigated (2000-2004)

The dynamic tensile strength of materials at load durations of a few microseconds or less is studied by analyzing the spall phenomena under shock pulse loading. The paper is devoted to discussing the methodology and capabilities of the technique to measure spall strength, its error sources, spall fracture of materials of different classes and the factors governing the high-rate fracture of metals and alloys under such conditions.

Spall fracture: methodological aspects, mechanisms and governing factors

The synthesis and characterisation of the nonsymmetric liquid crystal dimer, 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) is reported. An enantiotropic nematic (N)-twist-bend nematic (NTB) phase transition is observed at 109 °C and a nematic-isotropic phase transition at 153 °C. The NTB phase assignment has been confirmed using polarised light microscopy, freeze fracture transmission electron microscopy (FFTEM), (2)H-NMR spectroscopy, and X-ray diffraction. The effective molecular length in both the NTB and N phases indicates a locally intercalated arrangement of the molecules, and the helicoidal pitch length in the NTB phase is estimated to be 8.9 nm. The surface anchoring properties of CB6OCB on a number of aligning layers is reported. A Landau model is applied to describe high-resolution heat capacity measurements in the vicinity of the NTB-N phase transition. Both the theory and heat capacity measurements agree with a very weak first-order phase transition. A complementary extended molecular field theory was found to be in suggestive accord with the (2)H-NMR studies of CB6OCB-d2, and those already known for CB7CB-d4. These include the reduced transition temperature, TNTBN/TNI, the order parameter of the mesogenic arms in the N phase close to the NTB-N transition, and the order parameter with respect to the helix axis which is related to the conical angle for the NTB phase.

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Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl)hexane (CB6OCB) and comparison with CB7CB

Critical behavior of dielectric permittivity in the isotropic phase of nematogens

Results of studies of static dielectric permittivity (epsilon) and nonlinear dielectric effect (NDE) in the isotropic phase of 4-n-4'-isothiocyanatobiphenyl (nBT) homologous series from n = 2 to n = 10 exhibiting the isotropic-smectic E (I-SmE) transition, are presented. They are compared with results of similar studies in 4-cyano-4-n-alkylbiphenyls (nCB) from n = 4 to n = 12. In this homologous series isotropic-nematic (I-N) and isotropic-smectic-A (I-Sm-A) transitions take place. Despite significant differences between N, Sm-A, and Sm-E phases the same pretransitional behavior of epsilon and NDE in the isotropic phase, described by critical exponents gamma = 1 and alpha = 0.5, was found. It has been shown that when the length of the alkyl chain of a compound increases the discontinuity of the transition drops in nBT and rises in nCB. The influence of pressure on the discontinuity is also discussed.

Phase transitions from the isotropic liquid to liquid crystalline mesophases studied by linear and nonlinear static dielectric permittivity

The dynamics of glass is of importance in materials science but its nature has not yet been fully understood. Here we report that a verification of the temperature dependencies of the primary relaxation time or viscosity in the ultraslowing/ultraviscous domain of glass-forming systems can be carried out via the analysis of the inverse of the Dyre–Olsen temperature index. The subsequent analysis of experimental data indicates the possibility of the selfconsistent description of glass-forming low-molecular-weight liquids, polymers, liquid crystals, orientationally disordered crystals and Ising spin-glass-like systems, as well as the prevalence of equations associated with the ‘finite temperature divergence’. All these lead to a new formula for the configurational entropy in glass-forming systems. Furthermore, a link to the dominated local symmetry for a given glass former is identified here. Results obtained show a new relationship between the glass transition and critical phenomena.

/pdf/a-universal-description-of-ultraslow-glass-dynamics-8g45vou9t0.pdf

A universal description of ultraslow glass dynamics

Results are presented of temperature and pressure studies of static dielectric permittivity (epsilon) and the nonlinear dielectric effect (NDE) in the isotropic phase of smectogenic n-cyanobiphenyls: 9CB, 10CB, and 12CB (4-cyano-4'-n-alkylbiphenyl, n = 9, 10, and 12). For the mentioned properties, pretransitional effects can be well portrayed by applying the relations used for the isotropic phase of nematogens, where evidence of the quasicritical, fluidlike behavior with exponents alpha approximately 0.5 and gamma = 1 exists. This kind of behavior one can also observe on approaching the isotropic-smectic A transition. NDE studies in 10CB and 12CB made it possible to determine the pressure evolution of the discontinuity (delta T) of the I-SmA transition. It was found that pressure first decreases the discontinuity of the transition, and that next a gradual rise appears. This behavior is unlike the one observed for the isotropic-nematic transition, where only an increase of delta T with rising pressure was observed.

Quasicritical behavior of dielectric permittivity in the isotropic phase of smectogenic n-cyanobiphenyls

The application of a modified Simon-Glatzel-type relation [Z. Anorg. Allg. Chem. 178, 309 (1929)] for the pressure evolution of the glass temperature is presented, namely, Tg(P)=Tg0[1+ΔP∕(π+Pg0)]1∕bexp[−(ΔP∕c)], where (Tg0,Pg0) are the reference temperature and pressure, ΔP=P−Pg0, −π is the negative pressure asymptote, b is the power exponent, and c is the damping pressure coefficient. The discussion is based on the experimental Tg(P) data for magmatic silicate melt albite, polymeric liquid crystal P8, and glycerol. The latter data are taken from Cook et al. [J. Chem. Phys. 100, 5178 (1994)] and from the authors’ dielectric relaxation time (τ(P)) measurements, which employs the novel pressure counterpart of the Vogel-Fulcher-Tammann equation: τ(P)=τ0Pexp[DPΔP∕(P0−P)], where ΔP=P−PSL (PSL is the stability limit hidden under negative pressure), P0 is the estimation of the ideal glass pressure, and DP is the isothermal fragility strength coefficient. Results obtained suggest the hypothetical maximum of the T...

Aleksandra Drozd-Rzoska

Papers

Critical behavior of dielectric permittivity in the isotropic phase of nematogens

Phase transitions from the isotropic liquid to liquid crystalline mesophases studied by linear and nonlinear static dielectric permittivity

A universal description of ultraslow glass dynamics

Quasicritical behavior of dielectric permittivity in the isotropic phase of smectogenic n-cyanobiphenyls

On the glass temperature under extreme pressures.