DOCSLIB.ORG

Viscosity of Glass-Forming Liquids

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Viscosity of Glass-Forming Liquids Viscosity of glass-forming liquids John C. Mauroa,1, Yuanzheng Yueb, Adam J. Ellisona, Prabhat K. Guptac, and Douglas C. Allana aScience and Technology Division, Corning Incorporated, Corning, NY 14831; bSection of Chemistry, Aalborg University, DK-9000 Aalborg, Denmark; and cDepartment of Materials Science and Engineering, Ohio State University, Columbus, OH 43210 Communicated by J. C. Phillips, Rutgers University, Summit, NJ, October 9, 2009 (received for review June 15, 2009) The low-temperature dynamics of ultraviscous liquids hold the key ␶͑x͒ ␣͑x͒ ␩͑ ͒ ϭ ␩ ͑ ͒ ϩ ͩ ͪ to understanding the nature of glass transition and relaxation log T, x log ϱ x , [2] 10 10 T phenomena, including the potential existence of an ideal thermo- dynamic glass transition. Unfortunately, existing viscosity models, where ␩ϱ, ␶, and ␣ are fitting parameters. Eq. 2 had been such as the Vogel–Fulcher–Tammann (VFT) and Avramov–Milchev proposed (albeit empirically) by several authors (1, 7, 8) before (AM) equations, exhibit systematic error when extrapolating to the work of Avramov and Milchev. Although another three- low temperatures. We present a model offering an improved parameter model has recently been proposed by Elmatad et al. description of the viscosity–temperature relationship for both (9), the quadratic form adopted by these authors applies only inorganic and organic liquids using the same number of parame- over a narrow range of temperatures and breaks down in both the ters as VFT and AM. The model has a clear physical foundation high- and low-temperature tails. Here we are interested only in based on the temperature dependence of configurational entropy, those models, such as VFT and AM, that cover the full range of and it offers an accurate prediction of low-temperature isokoms temperatures by using a single three-parameter form. without any singularity at finite temperature. Our results cast doubt on the existence of a Kauzmann entropy catastrophe and Model. We revisit the problem of viscous liquid dynamics starting associated ideal glass transition. with the Adam–Gibbs equation (10), relating viscosity to the configurational entropy of the liquid, Sc(T,x): modeling ͉ supercooled liquids ͉ configurational entropy ͉ relaxation B͑x͒ PHYSICS ␩͑ ͒ ϭ ␩ ͑ ͒ ϩ log10 T, x log10 ϱ x , [3] erhaps the most intriguing feature of a supercooled liquid is TSc͑T, x͒ Pits dramatic rise in viscosity as it is cooled toward the glass transition. This sharp, super-Arrhenius increase is accompanied which has met with remarkable success in describing the relax- by very little change in the structural features observable by ation behavior of a wide variety of systems (11) and has proved typical diffraction experiments. Several basic questions remain a key enabler for the theoretical study of dynamical heteroge- unanswered: neities in supercooled liquids (12, 13). Here, B(x) is an effective 1. Is the behavior universal (i.e., is the viscosity of all liquids activation barrier, which is typically left as a fitting parameter. described by the same underlying model)? The configurational entropy Sc(T,x) is a complex quantity in a 2. Does the viscosity diverge at some finite temperature below glassily entangled system, but it can be modeled by using the glass transition (i.e., is there a dynamic singularity)? constraint theory. [Constraint theory is general approach that 3. Is the existence of a thermodynamic singularity the cause of has given an accurate description of the phase diagrams of the dramatic viscous slowdown? thermal, kinetic, vibrational, and other properties of many Answers to these questions are critical for understanding the network glasses, especially near the glass transition (14).] Fol- behavior of deeply supercooled liquids. Unfortunately, equilibrium- lowing the energy landscape analysis of Naumis (15) and the viscosity measurements cannot be carried out at temperatures temperature-dependent constraint model of Gupta and Mauro much below the glass transition owing to the long structural (16), the configurational entropy can be related to the topolog- relaxation time. It thus becomes critical to find a model that best ical degrees of freedom per atom (17, 18), f(T,x), by describes the temperature dependence of viscosity by using the ͑ ͒ ϭ ͑ ͒ ⍀ fewest possible number of fitting parameters (1, 2). Because two Sc T, x f T, x Nk ln , [4] parameters are needed for a simple Arrhenius description, mod- where N is the number of atoms, k is Boltzmann’s constant, and eling of super-Arrhenius behavior requires a minimum of three ⍀ is the number of degenerate configurations per floppy mode parameters. We focus on three-parameter models only, with the (16). To obtain the most economical model for f(T,x), we goal of describing the universal physics of supercooled liquid consider a simple two-state system in which the network con- viscosity in the most economical form possible. straints are either intact or broken, with an energy difference The most popular viscosity model is the Vogel–Fulcher– given by H(x): Tammann (VFT) equation (3) H͑x͒ A͑x͒ ͑ ͒ ϭ ͩ Ϫ ͪ ␩͑ ͒ ϭ ␩ ͑ ͒ ϩ f T, x 3exp . [5] log10 T, x log10 ϱ x Ϫ ͑ ͒ , [1] kT T T0 x In the limit of high temperature, Eq. 5 gives three translational T x where is temperature, is composition, and the three VFT degrees of freedom per atom. The network becomes completely ␩ϱ A T 1 parameters ( , , and 0) are obtained by fitting Eq. to rigid at absolute zero temperature, f(0,x) ϭ 0, where there is no experimentally measured viscosity data. In the polymer science thermal energy to break the bond constraints. Defining K(x) ϭ community, Eq. 1 is also known as the Williams–Landel–Ferry (WLF) equation (4). Although VFT has met with notable success for a variety of liquids, there is some indication that it Author contributions: J.C.M. designed research; J.C.M., A.J.E., P.K.G., and D.C.A. performed breaks down at low temperatures (3, 5). Another successful research; J.C.M., Y.Y., and A.J.E. analyzed data; and J.C.M., Y.Y., and P.K.G. wrote the paper. three-parameter viscosity model is the Avramov–Milchev (AM) The authors declare no conflict of interest. equation (6), derived based on an atomic hopping approach: 1To whom correspondence should be addressed. E-mail: [email protected]. www.pnas.org͞cgi͞doi͞10.1073͞pnas.0911705106 PNAS Early Edition ͉ 1of5 Downloaded by guest on September 23, 2021 ⍀ ϭ B(x)/3Nkln and C(x) H(x)/k, we obtain the following three- A 36 parameter model for viscosity: 32 VFT 28 AM K͑x͒ C͑x͒ 24 Current Model ␩͑ ͒ ϭ ␩ ͑ ͒ ϩ ͩ ͪ log10 T, x log10 ϱ x exp . [6] ) [Pa-s] 20 T T T / g 16 T ( 12 Eq. 6 was proposed empirically as one of several expressions by η Waterton in 1932 (19), but we are unaware of any subsequent 10 8 log 4 6 work with this expression. Although Eq. could be obtained by 0 assuming an exponential form for activation barrier in the -4 Arrhenius formula for viscosity, this would be physically unre- 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 alistic because (i) the activation barrier would become infinite in Tg/T the limit of zero temperature and (ii) the high-temperature B kinetics are dominated by entropic effects, which are not con- 6 ) VFT sidered by using a simple activation-barrier model. Here we 2 5 4 AM obtain Eq. 6 through a physically realistic model for configura- (1/K Current Model g 3 tional entropy based on a constraint approach. BT )/ 2 Although the viscosity models of Eqs. 1, 2, and 6 have different T ( c 1 sets of adjustable parameters, each model can be rewritten in S 0 terms of the same set of physically meaningful quantities: (i) the 0.0 0.2 0.4 0.6 0.8 1.0 glass-transition temperature, Tg(x); (ii) the fragility, m(x); and Tg/T (iii) the extrapolated infinite temperature viscosity, ␩ϱ(x). For 0.07 any composition x, the glass-transition temperature is defined C VFT ) 0.06 12 2 where the shear viscosity is equal to 10 Pa-s (16, 20), i.e., 0.05 AM 12 ␩(Tg(x),x) ϭ 10 Pa-s. Fragility (21) is defined as (1/K 0.04 Current Model g 0.03 BT Ѩ log ␩͑T, x͒ )/ 0.02 T 10 T ( ͯ c m͑x͒ ϭ . [7] 0.01 Ѩ͑ ͑ ͒ ͒ S Tg x /T ϭ ͑ ͒ T Tg x 0 0.0 0.2 0.4 0.6 0.8 1.0 With these definitions, the VFT expression of Eq. 1 becomes T/Tg ͑ Ϫ ␩ ͒2 12 log10 ϱ Fig. 1. Comparison of the viscosity models. (A) Temperature dependence of log ␩͑T͒ ϭ log ␩ϱ ϩ , [8] ϭ ␩ ϭϪ 10 10 ͑ Ϫ ͒ ϩ ͑ Ϫ ␩ ͒ viscosity with Eqs. 8–10, assuming m 60 and log10 ϱ 4. (B) Plot of Sc(T)/BTg m T/Tg 1 12 log10 ϱ for T Ͼ Tg, obtained by equating each of Eqs. 7-9 with the Adam–Gibbs the AM expression of Eq. 2 becomes relation of Eq. 3. The AM model of Eq. 9 yields a divergent configurational entropy in the limit of T 3ϱ.(C) Plot of Sc(T)/BTg for T Ͻ Tg. The VFT model of ͑ Ϫ ␩ ͒ ϭ T m/ 12 log10 ϱ Eq. 8 predicts a vanishing of configurational entropy at T T0. ␩͑ ͒ ϭ ␩ ϩ ͑ Ϫ ␩ ͒ͩ gͪ log T log ϱ 12 log ϱ , [9] 10 10 10 T remains contentious, the energy-landscape analysis of Stillinger and the current model in Eq.
Load more

Recommended publications
  • Structural Transformation in Supercooled Water Controls the Crystallization Rate of Ice
    Structural transformation in supercooled water controls the crystallization rate of ice. Emily B. Moore and Valeria Molinero* Department of Chemistry, University of Utah, Salt Lake City, UT 84112-0580, USA. Contact Information for the Corresponding Author: VALERIA MOLINERO Department of Chemistry, University of Utah 315 South 1400 East, Rm 2020 Salt Lake City, UT 84112-0850 Phone: (801) 585-9618; fax (801)-581-4353 Email: [email protected] 1 One of water’s unsolved puzzles is the question of what determines the lowest temperature to which it can be cooled before freezing to ice. The supercooled liquid has been probed experimentally to near the homogeneous nucleation temperature T H≈232 K, yet the mechanism of ice crystallization—including the size and structure of critical nuclei—has not yet been resolved. The heat capacity and compressibility of liquid water anomalously increase upon moving into the supercooled region according to a power law that would diverge at T s≈225 K,1,2 so there may be a link between water’s thermodynamic anomalies and the crystallization rate of ice. But probing this link is challenging because fast crystallization prevents experimental studies of the liquid below T H. And while atomistic studies have captured water crystallization3, the computational costs involved have so far prevented an assessment of the rates and mechanism involved. Here we report coarse-grained molecular simulations with the mW water model4 in the supercooled regime around T H, which reveal that a sharp increase in the fraction of four-coordinated molecules in supercooled liquid water explains its anomalous thermodynamics and also controls the rate and mechanism of ice formation.
    [Show full text]
  • 5: Viscosity of Glass
    MIT 3.071 Amorphous Materials 5: Viscosity of Glass Juejun (JJ) Hu 1 After-class reading list Fundamentals of Inorganic Glasses Ch. 9 Introduction to Glass Science and Technology Ch. 6 2 The pitch drop experiment The pitch drop experiment is a long-term experiment which measures the flow of a piece of pitch (asphalt) The most famous version of the experiment was started in 1927 by Professor Thomas Parnell of the University of Queensland in Brisbane, Australia. The eighth drop fell on 28 November 2000, allowing the experimenters to calculate that pitch has a viscosity approximately 230 Courtesy the University of Queensland on Wikimedia billion times that of water. Commons. License: CC BY-SA. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 3 Is glass a solid or a viscous liquid? “Successful read/write of digital data in fused silica glass with a recording density equivalent to Blu-ray Disc™, enabling both greater capacity using 100 recording layers and long storage life of 300 million years.” Hitachi Ltd. Press Release 2014 Image is in the public domain. Source: Wikimedia Commons. “It is well known that panes of stained glass in old European churches are thicker at the bottom because glass is a slow-moving liquid that flows downward over centuries.” Silica data storage disc © unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 4 Is glass a solid or a viscous
    [Show full text]
  • Ten Themes of Viscous Liquid Dynamics
    IOP PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 19 (2007) 205105 (8pp) doi:10.1088/0953-8984/19/20/205105 Ten themes of viscous liquid dynamics Jeppe C Dyre DNRF Centre ‘Glass and Time’, IMFUFA Building 27, Department of Sciences, Roskilde University, Postbox 260, DK-4000 Roskilde, Denmark Received 24 September 2006 Published 25 April 2007 Online at stacks.iop.org/JPhysCM/19/205105 Abstract Ten ‘themes’ of viscous liquid physics are discussed with a focus on how they point to a general description of equilibrium viscous liquid dynamics (i.e., fluctuations) at a given temperature. This description is based on standard time-dependent Ginzburg–Landau equations for the density fields, stress tensor fields, potential energy density field, and fields quantifying molecular orientations. One characteristic aspect of the theory is that density has the appearance of a non-conserved field. Another characteristic feature is the long-wavelength dominance of the dynamics, which not only simplifies the theory by allowing for an ultra-local Hamiltonian (free energy), but also explains the observed general independence of chemistry. Whereas there are no long-ranged static (i.e., equal-time) correlations in the model, there are important long-ranged dynamic correlations on the alpha timescale. 1. Introduction Glass-forming liquids approaching the calorimetric glass transition become extremely viscous, with viscosity 1013–1015 times than that of ambient water. These extreme viscosities reflect the fact that molecular motion has almost come to a standstill. Most molecular motion is vibrational in these liquids; thus a computer simulation of a liquid close to the calorimetric glass transition with present-day computers would not be able to distinguish it from a disordered solid.
    [Show full text]
  • Glass Transition
    Glass Transition U. Buchenau This document has been published in Manuel Angst, Thomas Brückel, Dieter Richter, Reiner Zorn (Eds.): Scattering Methods for Condensed Matter Research: Towards Novel Applications at Future Sources Lecture Notes of the 43rd IFF Spring School 2012 Schriften des Forschungszentrums Jülich / Reihe Schlüsseltechnologien / Key Tech- nologies, Vol. 33 JCNS, PGI, ICS, IAS Forschungszentrum Jülich GmbH, JCNS, PGI, ICS, IAS, 2012 ISBN: 978-3-89336-759-7 All rights reserved. E 9 Glass Transition U. Buchenau Institut fur¨ Festkorperforschung¨ Forschungszentrum Julich¨ GmbH Contents 1 Introduction 2 2 Kinetics of the glass transition 6 2.1 Fragility...................................... 6 2.2 Stretching and dynamical heterogeneity . ........ 7 3 Thermodynamics of the glass transition 10 3.1 TheKauzmanncatastrophe . 10 3.2 ThePrigogine-Defayratio . 11 4 New developments 12 4.1 Numericalsimulations . 12 4.2 Theoreticaldevelopments. 14 4.3 New experimental findings . 16 5 Summary 18 A The Prigogine-Defay ratio at a second order phase transition 19 0Lecture Notes of the 43rd IFF Spring School “Scattering Methods for Condensed Matter Research: Towards Novel Applications at Future Sources” (Forschungszentrum Julich,¨ 2012). All rights reserved. E9.2 U. Buchenau gas liquid volume glass crystal = 8 100s 1ns 1ps T T T T g m 0 c temperature Fig. 1: Volume-temperature diagram of the crystalline, glassy and liquid phase at ambient pressure. 1 Introduction The glass transition (the freezing of an undercooled and highly viscous liquid into a glass) is considered to be one of the great unsolved riddles of solid state physics. The main riddle is the atomic mechanism of the flow process in the highly viscous liquid and its strong temperature dependence shortly before freezing.
    [Show full text]
  • Novel Experimentally Observed Phenomena in Soft Matter
    PRAMANA c Indian Academy of Sciences Vol. 81, No. 1 — journal of July 2013 physics pp. 3–34 Novel experimentally observed phenomena in soft matter RANJINI BANDYOPADHYAY Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore 560 080, India E-mail: [email protected] MS received 10 October 2012; revised 24 April 2013; accepted 29 April 2013 Abstract. Soft materials such as colloidal suspensions, polymer solutions and liquid crystals are constituted by mesoscopic entities held together by weak forces. Their mechanical moduli are several orders of magnitude lower than those of atomic solids. The application of small to moderate stresses to these materials results in the disruption of their microstructures. The resulting flow is non-Newtonian and is characterized by features such as shear rate-dependent viscosities and non- zero normal stresses. This article begins with an introduction to some unusual flow properties displayed by soft matter. Experiments that report a spectrum of novel phenomena exhibited by these materials, such as turbulent drag reduction, elastic turbulence, the formation of shear bands and the existence of rheological chaos, flow-induced birefringence and the unusual rheology of soft glassy materials, are reviewed. The focus then shifts to observations of the liquid-like response of granular media that have been subjected to external forces. The article concludes with examples of the patterns that emerge when certain soft materials are vibrated, or when they are displaced with Newtonian fluids of lower viscosities. Keywords. Disperse systems; surfactant and micellar systems, associated polymers; polymer solutions; porous materials, granular materials; material behaviour; non-Newtonian fluid flows; patterns.
    [Show full text]
  • Liquid-To-Glass Transformation Simply Because This Is a Standalone Phenomenon
    MULTICOMPONENT SOLUTION SOLIDIFICATION WITH ARRESTED PHASE SEPARATION MODEL FOR GLASS TRANSITION Vladimir Belostotsky Kurnakov Institute of General and Inorganic Chemistry, RAS, Moscow, Russia* Abstract Due to nonuniform aggregation in liquid state, from thermodynamic point of view any glass- forming liquid approaching liquid-to-solid phase transition temperature, irrespective of the actual chemical composition, should be considered as a multicomponent solution whose species are comprised of the same chemical elements but vary in their size and shape, local density, structure, and stoichiometry. It is demonstrated that glass transition has to be regarded as a non- equilibrium solidification of the multicomponent solution where continuous attempts of the solid and liquid phases to separate out within solidification temperature range are jammed dynamically by rapid cooling, so that solidification occurs in the absence of solid-liquid interface. Bearing on this approach it is suggested how the difficulties in qualifying glass transformation as phase transition can be overcome. Keywords: Glass transition, nonuniform aggregation, multicomponent solution, segregationless solidification, phase transition. Subject classification codes: 64.70.Q-, 82.60.Lf, 83.80.Ab, 61.43.Hv. 1. Introduction In spite of being a very active area of exploration and thousands and thousands of publications for a century or so since the papers of Vogel [1], Fulcher [2], and Tamann and Hesse [3] have been published, the nature of glass transition and glassy state remains
    [Show full text]
  • 1 Copyrighted Material
    1 The Unique Nature of Glass Alexis G. Clare Kazuo Inamori School of Engineering, New York State College of Ceramics, Alfred University, Alfred, USA 1.1 WHAT IS GLASS? We tend to think of glass as a single material from which we manufacture many useful articles, such as windows, drinking vessels, and storage containers that can contain quite corrosive liquids, including aggressive laboratory chemicals. Therefore, the glass has to be quite corrosion- resistant and inert, including being able to maintain its optical properties while being in aggressive environments such as a dishwasher or extreme weather. For a material that we generally view as ‘‘delicate,’’ in terms of attack from chemicals, it can be quite resistant. Another extreme envi- ronment is the human body. An implanted medical device is subjected to a warm and wet environment with continual fluid flow and com- plex mechanicalCOPYRIGHTED loads, but perhaps more MATERIAL importantly there are many cells, some at work to reject foreign inert materials. They do this by encapsulating the materials with fibrous (scar) tissue. Hip replacements generally last 15 years or so, and in 2009 there was the story of a man who cut himself shaving and out of his chin fell a piece of glass. He had a lump under his chin, but he thought it was an abscess. In fact, 20 years Bio-Glasses: An Introduction, First Edition. Edited by Julian R. Jones and Alexis G. Clare. © 2012 John Wiley & Sons, Ltd. Published 2012 by John Wiley & Sons, Ltd. 2 BIO-GLASSES: AN INTRODUCTION earlier he was involved in a car accident and a piece of the windscreen embedded in his chin, unbeknown to him.
    [Show full text]
  • Liquidus Tracking: a Promising Vitrification Technique for Large Scale Encapsulated 3-D Cell Culture Preservation
    Liquidus Tracking: a promising vitrification technique for large scale encapsulated 3-D cell culture preservation A thesis submitted for the degree of Doctor of Philosophy (PhD) Eva Puschmann 2015 UCL Division of Surgery & Interventional Science Royal Free Campus Department of Surgery (in collaboration with) UCL Institute for Liver and Digestive Health Royal free Campus Devision of Medicine 1 Declaration I, Eva Puschmann confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in this thesis. 2 2 Abstract Liver organ shortage is an increasing problem worldwide and many die each year waiting for a new liver. In case of acute liver failure a bioartificial liver (BAL) device could “buy” time until a donor liver is available or until the liver has spontaneously undergone self-repair. For the clinical application of a BAL large quantities of cells should be available immediately necessitating cryo-banking. However, cryopreservation of large volumes results in increased ice formation and increased cell death. Ice formation can be prevented by vitrification, but the high cryoprotectant agent (CPA) concentrations needed are normally toxic to mammalian cells. Short exposure time minimizes toxicity but can only be achieved in small samples where fast cooling rates can be reached. To reduce CPA toxicity a vitrification machine (Liquidus Tracker) designed by Planer plc was used, which provides the lowest toxic effect that can be established for a given CPA concentration by decreasing the sample temperature to just above the melting point of that particular mix. The CPA concentration is then gradually increased as temperature is decreased along the liquidus curve.
    [Show full text]
  • The Old Problems of Glass and the Glass Transition, and the Many New Twists C
    Proc. Natl. Acad. Sci. USA Vol. 92, pp. 6675-6682, July 1995 Colloquium Paper This paper was presented at a colloquium entitled "Physics: The Opening to Complexity, " organized by Philip W. Anderson, held June 26 and 27, 1994, at the National Academy of Sciences, in Irvine, CA. The old problems of glass and the glass transition, and the many new twists C. A. ANGELL Department of Chemistry, Arizona State University, Tempe, AZ 85287-1604 ABSTRACT In this paper I review the ways in which the mediate range order (4), has been found (5-7) to correlate with glassy state is obtained both in nature and in materials science the temperature dependence of the viscosity (i.e., with the and highlight a "new twist"-the recent recognition of poly- so-called "fragility" of the liquid or polymer). At the same morphism within the glassy state. The formation of glass by time, the notion that a given liquid on slow cooling at constant continuous cooling (viscous slowdown) is then examined, the pressure always tends toward the same conformational ground strong/fragile liquids classification is reviewed, and a new state has recently been overturned by the recognition of the twist-the possibility that the slowdown is a result of an existence of polymorphism in the glassy state (8-11) [called avoided critical point-is noted. The three canonical charac- "polyamorphism" (12)]. Thus the field is in a state of flux. It teristics of relaxing liquids are correlated through the fragil- is an exciting period, as Anderson has opined (13), that a ity. As a further new twist, the conversion of strong liquids to theory of the nature of glass and the glass transition is the fragile liquids by pressure-induced coordination number in- "deepest and most interesting unsolved problem in solid state creases is demonstrated.
    [Show full text]
  • Glass Properties
    Cambridge University Press 0521580536 - Glasses for Photonics Masayuki Yamane and Yoshiyuki Asahara Excerpt More information 1 Glass properties Introduction Glass can be made with excellent homogeneity in a variety of forms and sizes, from small ®bers to meter-sized pieces. Furthermore, glass can be doped with rare earth ions and microcrystallites and a wide range of properties can be chosen to meet the needs of various applications. These advantages over crystalline materials are based on the unique structural and thermodynamic features of glass materials. Before discussing the special properties of glass, the fundamentals of glass materials are given in this chapter. 1.1 Features of glass as an industrial material 1.1.1 Structural features 1.1.1.1 Atomic arrangement A glass is de®ned in ASTM [1] as `an inorganic product of fusion which has been cooled to a rigid condition without crystallization'. According to this de®nition, a glass is a noncrystalline material obtained by a melt-quenching process. Nowadays, noncrystalline materials that can not be distinguished from melt-quenched glasses of the same composition are obtainable by using various techniques such as chemicalvapor deposition, sol-gelprocess,etc. Therefore, most glass scientists regard the term `glass' as covering `all noncrystalline solids that show a glass transition' regardless of their preparation method. The words `noncrystalline solids' and `glass transition' suggest that a glass cannot be classi®ed either in the category of crystalline materials such as quartz, sapphire, etc. or in the category of liquid. The atomic arrangement of a glass is different from those of crystalline materials and lacks long-range regularity, as schematically shown in Fig.
    [Show full text]
  • Microscopic-Phenomenological Model of Glass Transition and Temperature Dependence of Viscosity—Part I: Foundations of the Model
    ceramics Article Microscopic-Phenomenological Model of Glass Transition and Temperature Dependence of Viscosity—Part I: Foundations of the Model Karl Günter Sturm Diplom-Ingenieur (Chemie), Im Urbruch 3, D-63322 Rödermark, Germany; [email protected] Abstract: The glass transition is described as a time- and history-independent singular event, which takes place in an interval dependent on the distribution width of molecular vibration amplitudes. The intrinsic glass transition is not seen as a relaxation phenomenon, but is characterized by a fixed volumetric state at the glass temperature Tg0. The relaxation behavior of the transport properties depends on the distance to Tg0. Free volume is redefined and its generation is the result of the fluctuating transfer of thermal energy into condensed matter and the resulting combined interactions between the vibration elements. This creates vacancies between the elements which are larger than the cross-section of an adjacent element or parts thereof. Possible shifts of molecules or molecular parts through such apertures depend on the size and axis orientation and do not require further energetic activation. After a displacement, additional volume is created by delays in occupying abandoned positions and restoring the energetic equilibrium. The different possibilities of axis orientation in Citation: Sturm, K.G. space result in the different diffusive behavior of simple molecules and chain molecules, silicate Microscopic-Phenomenological network formers, and associated liquids. Glass transformation takes place at a critical volume Vg0 Model of Glass Transition and when the cross-section of apertures becomes smaller than the cross-section of the smallest molecular Temperature Dependence of parts. The glass transition temperature Tg0 is assigned to Vg0 and is therefore independent of Viscosity—Part I: Foundations of the molecular relaxation processes.
    [Show full text]
  • The Formation of Supercooled Brines, Viscous Liquids, and Low-Temperature Perchlorate Glasses in Aqueous Solutions Relevant to Mars ⇑ J.D
    Icarus 233 (2014) 36–47 Contents lists available at ScienceDirect Icarus journal homepage: www.elsevier.com/locate/icarus The formation of supercooled brines, viscous liquids, and low-temperature perchlorate glasses in aqueous solutions relevant to Mars ⇑ J.D. Toner a, , D.C. Catling a, B. Light b a University of Washington, Department of Earth & Space Sciences, Seattle, WA 98195, USA b Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA 98105, USA article info abstract Article history: Salt solutions on Mars can stabilize liquid water at low temperatures by lowering the freezing point of Received 10 July 2013 water. The maximum equilibrium freezing-point depression possible, known as the eutectic temperature, Revised 4 December 2013 suggests a lower temperature limit for liquid water on Mars; however, salt solutions can supercool below Accepted 19 January 2014 their eutectic before crystallization occurs. To investigate the magnitude of supercooling and its variation Available online 29 January 2014 with salt composition and concentration, we performed slow cooling and warming experiments on pure salt solutions and saturated soil-solutions of MgSO4, MgCl2, NaCl, NaClO4, Mg(ClO4)2, and Ca(ClO4)2.By Keywords: monitoring solution temperatures, we identified exothermic crystallization events and determined the Mars composition of precipitated phases from the eutectic melting temperature. Our results indicate that Ices Astrobiology supercooling is pervasive. In general, supercooling is greater in more concentrated solutions and with Mars, surface salts of Ca and Mg. Slowly cooled MgSO4, MgCl2, NaCl, and NaClO4 solutions investigated in this study typically supercool 5–15 °C below their eutectic temperature before crystallizing.
    [Show full text]