Critical phenomena and renormalization-group theory

Dynamic properties, derived from dielectric relaxation spectra of glass-formers at variable temperature and pressure, are used to characterize and classify any resolved or unresolved secondary relaxation based on their different behaviors. The dynamic properties of the secondary relaxation used include: (1) the pressure and temperature dependences; (2) the separation between its relaxation time τβ and the primary relaxation time τα at any chosen τα; (3) whether τβ is approximately equal to the independent (primitive) relaxation time τ0 of the coupling model; (4) whether both τβ and τ0 have the same pressure and temperature dependences; (5) whether it is responsible for the “excess wing” of the primary relaxation observed in some glass-formers; (6) how the excess wing changes on aging, blending with another miscible glass-former, or increasing the molecular weight of the glass-former; (7) the change of temperature dependence of its dielectric strength Δeβ and τβ across the glass transition temperature Tg; ...

Classification of secondary relaxation in glass-formers based on dynamic properties.

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

Evaluation of amorphous solid dispersion properties using thermal analysis techniques.

/pdf/dislocations-in-solids-1gaufoliyg.pdf

Dislocations in solids

Photoelastic response of permanently densified oxide glasses

We show that on cooling towards glass transition configurational entropy exhibits more significant changes than predicted by classic relation. A universal formula according to Kauzmann temperature [Formula: see text] is given: [Formula: see text], where [Formula: see text]. The exponent [Formula: see text] is hypothetically linked to dominated local symmetry. Such a behaviour is coupled to previtreous evolution of heat capacity [Formula: see text] associated with finite temperature singularity. These lead to generalised VFT relation, for which the basic equation is retrieved. For many glass-formers, basic VFT equation may have only an effective meaning. A universal-like reliability of the Stickel operator analysis for detecting dynamic crossover phenomenon is also questioned. Notably, distortions-sensitive and derivative-based analysis focused on previtreous changes of configurational entropy and heat capacity for glycerol, ethanol and liquid crystal is applied. 

/pdf/new-paradigm-for-configurational-entropy-in-glass-forming-2rtx8374.pdf

New paradigm for configurational entropy in glass-forming systems

Results of broadband dielectric spectroscopy and rheological studies of poly(propylene glycol) + SiO 2 nanocomposites are presented They show that the dynamics in high-concentrated composites is dominated by confinement and adsorption effects The most notable finding is the impact of nanoparticles on fragility, the fractional translational – orientational decoupling and the shift of dynamics towards the pure Vogel-Fulcher-Tammann pattern, associated with the lack of local symmetry preferences

New dynamics in poly(propylene glycol) based glass-forming nanocomposites

Results of broadband dielectric spectroscopy studies in liquid crystalline octyloxycyanobiphenyl (8OCB) and its colloids with BaTiO3 nanoparticles (paraelectric, diameter d = 50 nm) are presented. Studies were carried out in isotropic liquid, nematic, smectic A and solid crystalline phases. They are supported by derivative-based and distortion-sensitive analyses, revealing a set of universal scaling patterns for temperature evolution of static and dynamic dielectric properties. All these yielded evidence for a pretransitional fluctuation impact on the dielectric constant, primary relaxation time, loss curve maximum and translational-orientational decoupling associated with anomalous values of the fractional Debye-Stokes-Einstein (DSE) exponent 0.2 < S < 2.2. The evidence for critical like changes in a distribution of relaxation times is shown. For mesophases, a tiny addition of nanoparticles causes permanent orientation of LC molecules, leading even to a 16% increase of the dielectric constant above a maximal value in pure 8OCB. A split of two regions, dominated by pre-isotropic and pre-smectic fluctuations, is evidenced. Model explanations for detected phenomena, particularly in the isotropic liquid phase, are presented. New evidence for a premelting effect in the solid phase is also shown.

The fluctuation-driven dielectric properties of liquid crystalline 8OCB and its nanocolloids.

Results are presented for isothermal, pressure studies of the low frequency nonlinear dielectric effect in the isotropic phase of 8CB (isotropic — nematic (I-N) transition) and 12CB (isotropic — smectic(I-SmA transition). This made possible to determined the pressure dependence of the nematic and smectic clearing temperatures as well as the extrapolated temperatures of a hypothetical continuous phase transition up to P = 200 MPa. In the case of the I-N transition the discontinuity of the transition (ΔT) increases systematically with pressure while for the I-SmA transition ΔT decreases with rising pressure.

The Influence of High Pressure on the Discontinuity of the Isotropic - Nematic and the Isotropic — Smectic A Phase Transitions Studied by the Low-Frequency Nonlinear Dielectric Effect Measurements

Sylwester J. Rzoska

Papers

Photoelastic response of permanently densified oxide glasses

New paradigm for configurational entropy in glass-forming systems

New dynamics in poly(propylene glycol) based glass-forming nanocomposites

The fluctuation-driven dielectric properties of liquid crystalline 8OCB and its nanocolloids.

The Influence of High Pressure on the Discontinuity of the Isotropic - Nematic and the Isotropic — Smectic A Phase Transitions Studied by the Low-Frequency Nonlinear Dielectric Effect Measurements