Ultrastable glasses portray similar behaviour to ordinary glasses at high pressure.

C Rodríguez-Tinoco,J Ll Tamarit,M Barrio,J.-L Garden,P Lloveras,J Rodríguez-Viejo,M González-Silveira

doi:10.1038/srep34296

Abstract

Pressure experiments provide a unique opportunity to unravel new insights into glass-forming liquids by exploring its effect on the dynamics of viscous liquids and on the evolution of the glass transition temperature. Here we compare the pressure dependence of the onset of devitrification, Ton, between two molecular glasses prepared from the same material but with extremely different ambient-pressure kinetic and thermodynamic stabilities. Our data clearly reveal that, while both glasses exhibit different dTon/dP values at low pressures, they evolve towards closer calorimetric devitrification temperature and pressure dependence as pressure increases. We tentatively interpret these results from the different densities of the starting materials at room temperature and pressure. Our data shows that at the probed pressures, the relaxation time of the glass into the supercooled liquid is determined by temperature and pressure similarly to the behaviour of liquids, but using stability-dependent parameters.

Highlights

While the properties of the glass transition temperature have been deeply studied as a function of temperature by calorimetry in many different glasses, the pressure dependence of the calorimetric glass transition is a subject relatively little explored[18]
Two sets of Indomethacin samples, 20–40 μm thick UGs with Tf’ = 280 K, and CGs obtained by cooling the liquid at 2–10 K/min, with Tf’ = 315 K, were temperature-scanned at pressures ranging up to 300 MPa in a home-made high-pressure differential thermal analyser (HP-DTA)
The shape and the smaller overshoot of the DTA signal at the onset of devitrification, Ton, for pressures above 0.1 MPa are due to the lack of sensitivity of the HP-DTA setup, precluding a proper evaluation of the limiting fictive temperature as a function of pressure

Summary

Introduction

While the properties of the glass transition temperature have been deeply studied as a function of temperature by calorimetry in many different glasses, the pressure dependence of the calorimetric glass transition is a subject relatively little explored[18]. It has been found that glasses with strong molecular interaction of hydrogen bonding type, systematically show lower values of dTg/dP compared to glasses dominated by van der Waals forces[18,21,22,23]. Another universal feature of glasses is that over a sufficiently large pressure range the pressure dependence of Tg is non-linear, i.e. the effect of pressure on temperature weakens when pressure increases and can be adjusted with the empirical Andersson-Andersson equation[24], Tg. where κ1, κ2 and κ3 are empirical constants. We propose a tentative extension of our previous empirical model that aims to describe the relaxation dynamics of the system as a function of temperature and pressure by considering the dependence of density on these variables

Methods

Results

Conclusion