Soft glassy rheology of supercooled molecular liquids

Abstract

We probe the mechanical response of two supercooled liquids, glycerol and ortho-terphenyl, by conducting rheological experiments at very weak stresses. We find a complex fluid behavior suggesting the gradual emergence of an extended, delicate solidlike network in both materials in the supercooled state-i.e., above the glass transition. This network stiffens as it ages, and very early in this process it already extends over macroscopic distances, conferring all well known features of soft glassy rheology (yieldstress, shear thinning, aging) to the supercooled liquids. Such viscoelastic behavior of supercooled molecular glass formers is difficult to observe because the large stresses in conventional rheology can easily shear-melt the solid-like structure. glass transition ͉ glycerol ͉ ortho-terphenyl ͉ yield-stress

Aging and Solidification of Supercooled Glycerol

“…The first is a Couette geometry (Anton Paar CC 20) similar in dimensions to that used in Zondervan's study: 2 The gap size between inner and outer cylinder is 1 mm. The inner cylinder has a radius of 10 mm and is 30.1 mm long, with a conical bottom.…”

“…1 Most strikingly, the observed lifetime of the spatial heterogeneity is on the order of hours, about 6 orders of magnitude longer than the typical time for a glycerol molecule to reorient. Moreover, a recent experiment by Zondervan et al 2 has shown that the rheology of supercooled glycerol near the glass transition exhibits a novel viscoelastic behavior after sufficient aging of the sample. This was a surprising finding, given that supercooled liquids are thought to be pure Newtonian liquids whose viscosity diverges at the glass transition temperature T g .…”

“…We perform experiments first in a Couette geometry with similar dimensions as in Zondervan et al's study. 2 We monitor the linear response of supercooled glycerol as a function of aging time at different aging temperatures above the glass transition. We find that an initial slow cooling period is crucial for the formation of the solid-like state.…”

“…The storage modulus of the slushy phase is within an order of magnitude of the modulus found by Zondervan et al, although the aging temperatures were different (240 K vs 205 K). 2 When slowly heated, the slushlike phase eventually melts at the crystal melting point of glycerol which indicates that the slush either contains crystallites or turns into a crystal at higher temperatures.…”

The curious effect of potassium fluoride on glycerol carbonate. How salts can influence the structuredness of organic solvents

“…These materials exhibit distinctly non-liquid-like features, a soft glassy rheology, which make them very attractive for technological applications and intriguing systems in terms of physics of condensed matter [8,9]. Indeed, several technical applications take advantage of GC physico-chemical properties.…”