Activation volume in superpressed glass-formers

Aleksandra Drozd-Rzoska

doi:10.1038/s41598-019-49848-w

Aleksandra Drozd-Rzoska

Open Access

https://doi.org/10.1038/s41598-019-49848-w

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Abstract

In pressurized glass-forming systems, the apparent (changeable) activation volume Va(P) is the key property governing the previtreous behavior of the structural relaxation time (τ) or viscosity (η), following the Super-Barus behavior: {boldsymbol{tau }}{boldsymbol{(}}{boldsymbol{P}}{boldsymbol{)}}{boldsymbol{,}}{boldsymbol{eta }}{boldsymbol{(}}{boldsymbol{P}}{boldsymbol{)}}{boldsymbol{propto }}{bf{exp }}{boldsymbol{(}}{{boldsymbol{V}}}_{{boldsymbol{a}}}{boldsymbol{(}}{boldsymbol{P}}{boldsymbol{)}}{boldsymbol{/}}{boldsymbol{R}}{boldsymbol{T}}{boldsymbol{)}}, T = const. It is usually assumed that Va(P) = V#(P), where {{boldsymbol{V}}}^{{boldsymbol{#}}}{boldsymbol{(}}{boldsymbol{P}}{boldsymbol{)}}={boldsymbol{R}}{boldsymbol{T}}{boldsymbol{d}},{boldsymbol{ln}},{boldsymbol{tau }}{boldsymbol{(}}{boldsymbol{P}}{boldsymbol{)}}{boldsymbol{/}}{boldsymbol{d}}{boldsymbol{P}} or {{boldsymbol{V}}}^{{boldsymbol{#}}}{boldsymbol{(}}{boldsymbol{P}}{boldsymbol{)}}{boldsymbol{=}}{boldsymbol{R}}{boldsymbol{T}}{boldsymbol{d}},{boldsymbol{ln}},{boldsymbol{eta }}{boldsymbol{(}}{boldsymbol{P}}{boldsymbol{)}}{boldsymbol{/}}{boldsymbol{d}}{boldsymbol{P}}. This report shows that Va(P) ≪ V#(P) for P → Pg, where Pg denotes the glass pressure, and the magnitude V#(P) is coupled to the pressure steepness index (the apparent fragility). V#(P) and Va(P) coincides only for the basic Barus dynamics, where Va(P) = Va = const in the given pressure domain, or for P → 0. The simple and non-biased way of determining Va(P) and the relation for its parameterization are proposed. The derived relation resembles Murnaghan - O’Connel equation, applied in deep Earth studies. It also offers a possibility of estimating the pressure and volume at the absolute stability limit. The application of the methodology is shown for diisobutyl phthalate (DIIP, low-molecular-weight liquid), isooctyloxycyanobiphenyl (8*OCB, liquid crystal) and bisphenol A/epichlorohydrin (EPON 828, epoxy resin), respectively.

Highlights

Previtreous changes of the structural relaxation time (τ), viscosity (η), electric conductivity (σ), heat conductivity (κ), diffusion (d) or chemical reactions rates (k) in systems ranging from low-molecular-weight liquids and polymers to liquid crystals and plastic crystals are the key manifestation of the hypothetical universal dynamics emerging on approaching the glass transition (Tg, Pg)[1,2,3,4,5]
When discussing the physical meaning of V#(P) one can recall the definition of the pressure-related steepness index in the previtreous domain[8], which leads to the relation: www.nature.com/scientificreports
( ) ( ) It terminates at the pressure-related fragility[11]: mT = mT Pg dlog10τ(P)/d

Summary

Introduction

Previtreous changes of the structural (primary, alpha) relaxation time (τ), viscosity (η), electric conductivity (σ), heat conductivity (κ), diffusion (d) or chemical reactions rates (k) in systems ranging from low-molecular-weight liquids and polymers to liquid crystals and plastic crystals are the key manifestation of the hypothetical universal dynamics emerging on approaching the glass transition (Tg, Pg)[1,2,3,4,5]. The temperature path is associated with the Super-Arrhenius (SA) dynamics, and it is governed by changes of the apparent activation energy Ea(T), which strongly increases on approaching the glass transition temperature Tg9–11. For compressed glass-formers, general features of the previtreous dynamics are described by the Super-Barus (SB) equation[7,8,9,10]: τ(P). Similar SB dependences describe pressure changes of all physical properties recalled above: pressure dependences of τ(P) and η(P) are parallel (Eq (1))[6,7,8], but for the remaining dynamic properties the translational - orientational decoupling have to be taken into account[8,10]. For DC electric conductivity[16]: σ−1(P)

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