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

Nonlinear dielectric effect (NDE) describes changes of dielectric permittivity induced by a strong electric field in a liquid dielectric. The most classical finding related to this magnitude is the negative sign of NDE in liquid diethyl ether (DEE), recalled by Peter Debye in his Nobel Prize lecture. This article shows that the positive sign of NDE in DEE is also possible, in the supercritical domain. Moreover, NDE on approaching the gas-liquid critical point exhibits a unique critical effect described by the critical exponent ψ ≈ 0.4 close to critical temperature (T C) and ψ ≈ 0.6 remote from T C . This can be linked to the emergence of the mean-field behavior in the immediate vicinity of T C , contrary to the typical pattern observed for critical phenomena. The multi-frequency mode of NDE measurements made it possible to estimate the evolution of lifetime of critical fluctuations. The new way of data analysis made it possible to describe the critical effect without a knowledge of the non-critical background contribution in prior.

Nonlinear dielectric effect in supercritical diethyl ether

Segmental relaxation in a series of polymethylphenylsiloxanes (PMPS) was studied using dielectric spectroscopy. The measurements covered a temperature range of more than 40 deg at pressures from ambient to 115 MPa. The results confirmed that the shape of the loss peak is independent of temperature, pressure and molecular weight. Consequently, the Tg -scaled dependence of the relaxation times was also independent of molecular weight. The pressure dependence of the relaxation times was characterized by means of the activation volume. This quantity changes markedly with pressure at a given temperature. However, the activation volume at the respective glass transition temperatures of the PMPS are essentially invariant to molecular weight. Finally, we measured the dependence of Tg on pressure, with the results well-described by the Andersson equation.

/pdf/effect-of-temperature-and-pressure-on-segmental-relaxation-24jcaetoxe.pdf

Effect of Temperature and Pressure on Segmental Relaxation in Polymethylphenylsiloxane

Obtaining a combination of high toughness and strength is crucial for most structural materials, but unfortunately these tend to be mutually exclusive. The search for strong and tough damage-resistant materials has thus typically been based on achieving an acceptable compromise between hardness and crack resistance. Focusing here on brittle oxide glasses, we propose a new strategy for overcoming this conflict by identifying new structural motifs for designing hard and crack-resistant glasses. Specifically, we report that surprisingly there is no decrease in the densification contribution to deformation of a mixed network ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}\ensuremath{-}{\mathrm{B}}_{2}{\mathrm{O}}_{3}\ensuremath{-}{\mathrm{P}}_{2}{\mathrm{O}}_{5}\ensuremath{-}\mathrm{Si}{\mathrm{O}}_{2}$ bulk glass following predensification of the glass at elevated temperature. Hitherto unique to this glass composition, the treatment reduces the residual stress during subsequent sharp contact loading, which in turn leads to a simultaneous increase in hardness and crack resistance. Based on structural characterization, we show that the more densified medium-range order of the hot compressed glass results in formation of certain structural states (e.g., nonring trigonal boron), which could not be reached through any composition or thermal path. This work thus shows that accessing such ``forbidden'' structural states through the identified densification at elevated temperatures offers a way forward to overcome the conflict of strength versus toughness in structural materials.

/pdf/combining-high-hardness-and-crack-resistance-in-mixed-3ea96ddrbd.pdf

Combining high hardness and crack resistance in mixed network glasses through high-temperature densification

Nonlinear dielectric effect in a pure and in a nitrobenzene-doped critical solution of perfluoromethylcyclohexane-carbon tetrachloride

Critical behavior of the isotropic-smectic-A transition in p-decyloxy-benzylidene-p-amino-2-methyl-butyl-cinnamate studied by the nonlinear dielectric effect method.

Sylwester J. Rzoska

Papers

Nonlinear dielectric effect in supercritical diethyl ether

Effect of Temperature and Pressure on Segmental Relaxation in Polymethylphenylsiloxane

Combining high hardness and crack resistance in mixed network glasses through high-temperature densification

Nonlinear dielectric effect in a pure and in a nitrobenzene-doped critical solution of perfluoromethylcyclohexane-carbon tetrachloride

Critical behavior of the isotropic-smectic-A transition in p-decyloxy-benzylidene-p-amino-2-methyl-butyl-cinnamate studied by the nonlinear dielectric effect method.