The rheology of solid glass (original) (raw)

Soft glassy rheology of supercooled molecular liquids

Proceedings of the National Academy of Sciences, 2008

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. The work presented here, combined with evidence for long-lived heterogeneity from previous single-molecule studies [Zondervan R, Kulzer F, Berkhout GCG, Orrit M (2007) Local viscosity of supercooled glycerol near Tg probed by rotational diffusion of ensembles and single dye molecules. Proc Natl Acad Sci USA 104:12628 -12633], has a profound impact on the understanding of the glass transition because it casts doubt on the widely accepted assumption of the preservation of ergodicity in the supercooled state.

Understanding Slow and Heterogeneous Dynamics in Model Supercooled Glass-Forming Liquids

ACS Omega

Glasses are ubiquitous in nature. Many common items such as ketchups, cosmetic products, toothpaste, etc. and metallic glasses are examples of such glassy materials whose dynamical and rheological properties matter in our daily life. The dynamics of these glass-forming systems are known to be very sluggish and heterogeneous, but a detailed understanding of the origin of such slowing down is still lacking. Slow heterogeneous dynamics occur in a wide variety of systems at scales ranging from microscopic to macroscopic. Polymeric liquids, granular material, such as powder and sand, gels, and foams and also metallic alloys show such complex glassy dynamics at appropriate conditions. Recently, the existence of dynamical heterogeneity has also been found in biological systems starting from collective cell migration in a monolayer of cells to embryonic morphogenesis, cancer invasion, and wound healing. Extensive research in the past decade or so lead to the understanding that there are growing dynamic and static correlation lengths associated with the observed dynamical heterogeneity and rapid rise in viscosity. In this review, we have highlighted the recent developments on measuring these correlation lengths in glass-forming liquids and their possible implications in the physics of the glass transition.

On the dynamics of liquids in their viscous regime approaching the glass transition

The European Physical Journal E, 2012

Recently, Mallamace et al. (Eur. Phys. J. E 34, 94 (2011)) proposed a crossover temperature, T(×), and claimed that the dynamics of many supercooled liquids follow an Arrhenius-type temperature dependence between T(×) and the glass transition temperature T(g). The opposite, namely super-Arrhenius behavior in this viscous regime, has been demonstrated repeatedly for molecular glass-former, for polymers, and for the majority of the exhaustively studied inorganic glasses of technological interest. Therefore, we subject the molecular systems of the Mallamace et al. study to a "residuals" analysis and include not only viscosity data but also the more precise data available from dielectric relaxation experiments over the same temperature range. Although many viscosity data sets are inconclusive due to their noise level, we find that Arrhenius behavior is not a general feature of viscosity in the T(g) to T(×) range. Moreover, the residuals of dielectric relaxation times with respect to an Arrhenius law clearly reveal systematic curvature consistent with super-Arrhenius behavior being an endemic feature of transport properties in this viscous regime. We also observe a common pattern of how dielectric relaxation times decouple slightly from viscosity.

Mechanical response of a simple molecular glass former in the glass transition region

2006

Dynamic shear modulus measurements have been performed on a simple glass forming liquid, m-toluidine, as a function of frequency at low temperatures, down to the glass transition region. This approach, based on isothermal experiments, has allowed the study of various aspects of the mechanical response of the supercooled liquid: the glass-like behaviour (low temperatures/high frequencies), the liquid-like behaviour (viscous flow at high temperatures/low frequencies), and the relaxational behaviour. The information obtained from the analysis of the complex frequencydependent shear modulus has been exploited to focus on: (a) the properties of the ␣-relaxation process in the supercooled liquid around its glass transition temperature, (b) the possible existence of a ␤-relaxation process, and (c) the low viscosity of m-toluidine at the glass transition, compared to other glass-formers.

Supercooled dynamics of glass-forming liquids and polymers under hydrostatic pressure

Reports on Progress in Physics, 2005

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.

Relaxation oscillation of borosilicate glasses in supercooled liquid region

Scientific Reports, 2017

Most supercooled non-polymeric glass-forming melts exhibit a shear thinning phenomenon, i.e., viscosity decreases with increasing the strain rate. On compressing borosilicate glasses at high temperature, however, we discovered an interesting oscillatory viscous flow and identified it as a typical relaxation oscillation caused by the peculiar structure of borosilicate glass. Specifically, the microstructure of borosilicate glass can be divided into borate network and silicate network. Under loading, deformation is mainly localized in the borate network via a transformation from the three coordinated planar boron to trigonal boron that could serve as a precursor for the subsequent formation of a BO 4 tetrahedron, while the surrounding silicate network is acting as a stabilization/relaxation agent. The formation of stress oscillation was further described and explained by a new physics-based constitutive model. The nonlinear rheology of glassy materials is at the very centre of non-crystalline physics and mechanics 1-4 , which represents the complex deformation mechanisms of a variety of advanced amorphous materials including soft-matter colloidal suspensions, polymer melts, gels, forms, structural glasses as well as metallic glasses 4,5. Although significant emphasis has been dedicated in recent years to the dynamic heterogeneity 5,6 , Phillips-Thorpe Rigidity Theory 7-11 , spatial collective flow 2,3,5 and jamming 1,12,13 in simple glassy systems, studying the nonlinear rheology of complicated structural glasses remains challenging. The rheological nonlinearities of structural glasses arise from the metastability, topological rigidity and heterogeneity of the network structure 7-11 and its relaxation 14-17. According to the classic Maxwell equation η = Gτ 18 , the viscosity η of a glass in its supercooled liquid region (SLR) is directly related to the infinite frequency shear elastic modulus G and the shear relaxation time τ. If the temperature is high, the small relaxation time can quickly release the dynamic heterogeneity of structure produced by external loading, which is characterized as a Newtonian fluid. However, if the temperature approaches the material's glass transition temperature (T g), the unrelaxed dynamic heterogeneity will lead to rheological nonlinearity, i.e., non-Newtonian. Studying the nonlinear rheology of structural glass in its SLR is critical, not only for gaining the fundamental understanding of glass science, but also for improving the many advanced techniques used in the production of ultra-precision glass components 19. According to the dependence of strain rate, the non-Newtonian liquid can be further divided into two groups: shear thickening flow if the viscosity increases with strain rate, and shear thinning flow if the viscosity decreases with strain rate 20. Generally, traditional silicate melts have a shear thinning flow 21 , while shear thickening flow was only found in some colloid glasses or suspensions 20. Lubchenko stated that 22 all deeply super-cooled non-polymeric fluids, independent of their chemical details, should exhibit simple shear thinning. This statement was further supported by recent experimental results covering a wide range of inorganic glass-forming liquids including

Short time dynamics of glass-forming liquids

The Journal of Chemical Physics, 1995

Calculations have been presented for the intermediate scattering function, dynamic structure factor, and dynamic susceptibility of a complex correlated system undergoing relaxation with independent vibrations. The vibrational contribution was approximated by a Debye spectrum, smoothed at high frequency, while the coupling model was used to describe the relaxation. This model asserts for nonpolymeric glass-forming liquids a crossover at a microscopic time from intermolecularly uncorrelated relaxation at a constant rate to intermolecularly coupled relaxation with a time-dependent, slowed-down rate. Although the model has previously been employed to successfully predict and otherwise account for a number of macroscopic relaxation phenomena, critical phenomena are not included in, and cannot be addressed by, the coupling model. Notwithstanding an absence of any change in transport mechanism for the supercooled liquid at a critical temperature, the coupling model data, when analyzed in t...

Rheology of hard glassy materials

Journal of Physics: Condensed Matter

Glassy solids may undergo a fluidization (yielding) transition upon deformation whereby the material starts to flow plastically. It has been a matter of debate whether this process is controlled by a specific time scale, from among different competing relaxation/kinetic processes. Here, two constitutive models of cage relaxation are examined within the microscopic model of nonaffine elasto-plasticity. One (widely used) constitutive model implies that the overall relaxation rate is dominated by the fastest between the structural (α) relaxation rate and the shearinduced relaxation rate. A different model is formulated here which, instead, assumes that the slowest (global) relaxation process controls the overall relaxation. We show that the first model is not compatible with the existence of finite elastic shear modulus for quasistatic (low-frequency) deformation, while the second model is able to describe all key features of deformation of 'hard' glassy solids, including the yielding transition, the nonaffine-to-affine plateau crossover, and the rate-stiffening of the modulus. The proposed framework provides an operational way to distinguish between 'soft' glasses and 'hard' glasses based on the shear-rate dependence of the structural relaxation time.