Glass Transition Phenomenon Research Articles

Thermal characterization of static and dynamical properties of the confined molecular systems interacting through dispersion force

We investigated the thermal properties of liquid methylcyclohexane and racemic sec-butylcyclohexane, as representatives of a molecular system with only dispersion-force intermolecular interactions, confined in the pores (thickness/diameter d = 12, 6, 1.1 nm) of silica gels by adiabatic calorimetry. The results imply a heterogeneous picture for molecular aggregate under confinement consisting of an interfacial region and an inner pore one. In the vicinity of a glass-transition temperature Tg,bulk of bulk liquid, two distinguishable relaxation phenomena were observed for the confined systems and their origins were attributed to the devitrification, namely glass transition, processes of (1) a layer of interfacial molecules adjacent to the pore walls and (2) the molecules located in the middle of the pore. A third glass-transition phenomenon was observed at lower temperatures and ascribed to a secondary relaxation process. The glass transition of the interfacial-layer molecules was found to proceed at temperatures rather above Tg,bulk, whereas that of the molecules located in the inner pore region occurred at temperatures below Tg,bulk. We discuss the reason why the molecules located in different places in the pores reveal the respectively different dynamical properties.

Investigation on Powder Content Ratio in Shaving Process of <i>Katsuobushi </i>with Various Moisture Content by Considering Glass Transition Phenomena

Investigation on Powder Content Ratio in Shaving Process of <i>Katsuobushi </i>with Various Moisture Content by Considering Glass Transition Phenomena

Thermal behavior of Se-rich Ge2Sb2Se(5−y)Tey chalcogenide system

The thermal behavior of the Ge2Sb2Se(5−y)Tey chalcogenide system (a compositional analog of the famous GST-225 PCM material) was thoroughly studied. Glass transition, cold crystallization, and melting phenomena were investigated in dependence on composition and various experimental conditions (heating rate, particle size). The kinetics of the structural relaxation and crystallization processes are described in terms of the Tool–Narayanaswamy–Moynihan and Autocatalytic models. The complexity of these processes is thoroughly discussed with regard to the compositionally given changes of molecular structures. Heat capacity measurements were performed for the compositions with y=0, 0.5, and 1 in the 50–550°C temperature range. All glassy and crystalline Cp dependences were found to be identical within the experimental error. The compositional dependence of the P-type undercooled liquid Cp evolution was found to contribute significantly to the changes in glass-forming ability (GFA). The GFA trend was discussed in terms of the mutual interplay between the thermodynamics and kinetics in this system.

On a new class of integro-differential equations

We consider various initial-value problems for ordinary integro-differential equations of first order that are characterized by convolution-terms, where all factors depend on the solutions of the equations. Applications of such problems are descriptions of certain glass-transition phenomena based on mode-coupling theory, for instance. We will prove results concerning well-posedness of such problems and the asymptotic behaviour of their solutions.

Grand Challenges in Glass Science

INTRODUCTION Glass science offers researchers an ample range of open questions, starting from one of the most difficult problems in science: the basic nature of the glassy state. Atomic-level descriptions of the glassy state are extremely complex due to the lack of long-range order found in crystalline materials. Our understanding of fundamental glass physics and chemistry is also hindered by the non-equilibrium thermodynamic state of glass. Recent theoretical and experimental advances are enabling the field to mature from an empirical discipline to one built upon rigorous scientific principles. These advancements not only offer a remarkable level of understanding but also contribute to the atomic-level design of novel functional glasses (Mauro et al., 2013a). Glass science combines the cutting edge of a multitude of technical subjects: physics, chemistry, geology, engineering, and mathematics. Glass transition and relaxation phenomena are at the frontiers of condensed matter and statistical physics. From a chemical perspective, a nearly infinite combination of compositions can lead to successful glass formation. To facilitate progress at a large scale and exploit all of the unique properties that glasses may offer, the boundaries of glass engineering technology must also be pushed forward. Recent advances of the domain have coincided with an unprecedented demand for glass as a high-tech material in consumer electronic devices. Working in the field of glass has never been more stimulating – glass plays a critical role in solving several of the global energy and healthcare challenges of today.

The β-relaxation in metallic glasses

Abstract Focusing on metallic glasses as model systems, we review the features and mechanisms of the β-relaxations, which are intrinsic and universal to supercooled liquids and glasses, and demonstrate their importance in understanding many crucial unresolved issues in glassy physics and materials science, including glass transition phenomena, mechanical properties, shear-banding dynamics and deformation mechanisms, diffusion and the breakdown of the Stokes–Einstein relation as well as crystallization and stability of glasses. We illustrate that it is an attractive prospect to incorporate these insights into the design of new glassy materials with extraordinary properties. We also outline important questions regarding the nature of β-relaxations and highlight some emerging research directions in this still-evolving field.

Application of Glass Transition in Food Processing

The phenomenon of glass transition has been employed to food products to study their stability. It can be applied as an integrated approach along with water activity and physical and chemical changes in food in processing and storage to determine the food stability. Also associated with the changes during agglomeration crystallization, caking, sticking, collapse, oxidation reactions, nonenzymatic browning, and microbial stability of food system. Various techniques such as Differential Scanning Calorimetry, Nuclear Magnetic Resonance, etc. have been developed to determine the glass transition temperature (Tg) of food system. Also, various theories have been applied to explain the concept of Tg and its relation to changes in food system. This review summarizes the understanding of concept of glass transition, its measurement, and application in food technology.

X-ray reflectivity study of the glass transition temperature of thin films

The glass transition takes place in amorphous materials (like polymers) during heating or cooling, and can be described as reversible transition from a hard and brittle state into a rubber-like state. Although physical properties of the material change significantly during the glass transition, this is not a phase transition of the material. The temperature at which the transition between the glassy and rubbery state occurs is called the glass transition temperature, and this temperature is always lower than the melting temperature. Thermodynamically, the glass transition is associated with transfer of heat between the system and its surrounding and with an abrupt volume change. Previously it was shown that the glass transition temperature of nano-films is different from that of bulk materials [1], which signifies the importance of determining this parameter for such systems. In the current work, we use quick X-ray reflectivity (qXRR) measurements to determine the glass transition temperature of polyvinyl acetate (PVAc). PVAc is rubbery synthetic polymer with the formula (C4H6O2), a density of 1.18 g/cm3, and a glass transition temperature for bulk material of 30oC [2]. Regular X-ray reflectivity measurements are based on θ/2θ scans at grazing incidence and typically require 0.5-1.5 h for a single scan. The qXRR technique is based on simultaneous measurement of the whole angular x-ray reflectivity profile and is suitable for in-situ measurement without moving the sample and/or the x-ray optics. Thus, the qXRR technique allows for very fast measurement of the x-ray reflectivity curves (duration of each scan is typically 0.1–20 sec [3]), which permits studying the time evolution of chemical, thermal, and mechanical changes at the surface and interface of different materials. X-ray reflectivity measurements give information about both density and thickness of thin films, and are suitable for studying glass transition phenomena. Nano-thickness PVAc layers on a Si substrate were examined with the qXRR technique, with x-ray reflectivity scans (each 10-seconds in duration) being recorded while temperature was changed from 20 to 50oC (total of 331 scans over 7 hours and 46 minutes). In the current paper, the experimental setup, the data-processing, and the analysis of the results from the qXRR measurements will be presented.

Pomegranate Seed Oil‐Loaded Particles of the Zein Cross‐Linked with Citric Acid

AbstractZein was cross‐linked chemically with citric acid in the presence of sodium hydroxide as the reaction catalyst. Water was then used to desolvate the zein and generate core‐free or pomegranate seed oil‐loaded particles. Mean size of the particles obtained from noncross‐linked and cross‐linked zein was 350 and 246 nm, respectively. Cross‐linking reaction caused an increase in the oil encapsulation efficiency. Scanning electron microscopy revealed the spherical morphology of particles. Fourier transform infrared (FTIR) spectroscopy confirmed the occurrence of chemical linkages between citric acid and zein. As well, it suggested that oil entrapment inside the zein particles was merely physical. Particulation of zein increased the upper limit of the glass transition phenomenon of biopolymer from 78C to ∼120C. The glass transition temperature (Tg) was also affected by the cross‐linking of zein and oil encapsulation. The amount of encapsulated oil released from particles via the peptic hydrolysis was lower for the cross‐linked sample.Practical ApplicationsMany biologically active ingredients including the pomegranate seed oil are extensively susceptible to oxidation, as well as, some are hydrolyzed considerably by enzymes leading to diminished bioactivity. Encapsulation of these hydrophobic cores within sub‐micron zein particles generated via desolvation with water (an easily scale‐up able method) leads not only to increased oxidative stability but also the wider application of core in aqueous foods. Citric acid‐mediated cross‐linking of zein molecules before the desolvation stage increased considerably the gastric digestion stability of particles, which assures that the encapsulated core may pass the stomach without being hydrolyzed with pepsin or acid. The particles prepared from the cross‐linked zein were also more heat resistant. This suggested that the particles can be heat‐treated to higher temperatures in food processing practices.

Pressure dependence of glass transition in As2Te3 glass.

Amorphous solids prepared from their melt state exhibit glass transition phenomenon upon heating. Viscosity, specific heat, and thermal expansion coefficient of the amorphous solids show rapid changes at the glass transition temperature (Tg). Generally, application of high pressure increases the Tg and this increase (a positive dT(g)/dP) has been understood adequately with free volume and entropy models which are purely thermodynamic in origin. In this study, the electrical resistivity of semiconducting As(2)Te(3) glass at high pressures as a function of temperature has been measured in a Bridgman anvil apparatus. Electrical resistivity showed a pronounced change at Tg. The Tg estimated from the slope change in the resistivity-temperature plot shows a decreasing trend (negative dT(g)/dP). The dT(g)/dP was found to be -2.36 °C/kbar for a linear fit and -2.99 °C/kbar for a polynomial fit in the pressure range 1 bar to 9 kbar. Chalcogenide glasses like Se, As(2)Se(3), and As(30)Se(30)Te(40) show a positive dT(g)/dP which is very well understood in terms of the thermodynamic models. The negative dT(g)/dP (which is generally uncommon in liquids) observed for As(2)Te(3) glass is against the predictions of the thermodynamic models. The Adam-Gibbs model of viscosity suggests a direct relationship between the isothermal pressure derivative of viscosity and the relaxational expansion coefficient. When the sign of the thermal expansion coefficient is negative, dT(g)/dP = Δk/Δα will be less than zero, which can result in a negative dT(g)/dP. In general, chalcogenides rich in tellurium show a negative thermal expansion coefficient (NTE) in the supercooled and stable liquid states. Hence, the negative dT(g)/dP observed in this study can be understood on the basis of the Adams-Gibbs model. An electronic model proposed by deNeufville and Rockstad finds a linear relation between Tg and the optical band gap (Eg) for covalent semiconducting glasses when they are grouped according to their average coordination number. The electrical band gap (ΔE) of As(2)Te(3) glass decreases with pressure. The optical and electrical band gaps are related as Eg = 2ΔE; thus, a negative dT(g)/dP is expected when As(2)Te(3) glass is subjected to high pressures. In this sense, As(2)Te(3) is a unique glass where its variation of Tg with pressure can be understood by both electronic and thermodynamic models.

Correlation between glass transition and crystallization phenomena in context of Meyer–Neldel rule

The physical origin of the glass transition and its possible connection with crystallization is still an unresolved problem of glass science. Recent publications demonstrate the strong evidence of intrinsic relation between glass transition and crystallization phenomena. Here, we study this problem by using Meyer–Neldel rule (MNR) as a tool. The observation of MNR in thermally activated non-isothermal crystallization was verified by us in past. The objective of the present work is to check the applicability of MNR for thermally activated non-isothermal glass transition and crystallization in some chalcogenide glasses. We found that like crystallization, the glass transition phenomenon also obeys the MNR.

Dynamic Mechanical Relaxation in Bulk Metallic Glasses: A Review

Metallic glasses have aroused considerable interest in the past decades because they exhibit fascinating properties. First, this article briefly outlines the mechanical, thermal properties and application of the metallic glasses. In addition, we focus on the dynamic mechanical relaxation behaviors, i.e. main (α) and secondary (β) relaxations, in metallic glasses. The mechanical relaxation behaviors are connected to the mechanical properties and physical properties in glassy materials. The main relaxation in glassy materials is related to the glass transition phenomenon and viscous flow. On the other hand, the β relaxation is linked to many fundamental issues in metallic glasses. In these materials relaxation processes are directly related to the plastic deformation mechanism. The mechanical relaxations, particularly, the β relaxation provides an excellent opportunity to design metallic glasses with desired physical and mechanical properties. We demonstrate the universal characteristics of main relaxation in metallic glasses. The phenomenological models and the physical theories are introduced to describe the main relaxation in metallic glasses. In parallel, we show the dependence of the α and β relaxations on the thermal treatments in metallic glasses. Finally, we analyze the correlation between the atomic mobility and the thermo-mechanical treatments in metallic glasses. On the one hand, the atomic mobility in metallic glasses is reduced by physical aging or crystallization. On the other hand, the atomic mobility in metallic glass is enhanced by deformation (i.e. compression and cold rolling). Importantly, to analyze the atomic mobility in amorphous materials, a physical theory is introduced. This model invokes the concept of quasi-point defects, which correspond to the density fluctuations in the glassy materials.

TSDC and DSC Study of Effects of Physical Aging on Polybutylene Terephthalate (PBT)

The impact of the physical aging process on the electrical and thermal properties of semicrystalline polybutylene terephthalate (PBT) was investigated by means of thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC). The TSDC technique was used to study the relaxation modes of PBT in the temperature range −50° to + 120°C. The obtained spectra revealed two peaks located at temperature maxima of 45° and 93°C. The peak appearing at 45°C corresponds to the dielectric manifestation of the glass transition phenomenon (α-relaxation). The aim of this work is to study the effect of physical aging on this relaxation. The recording of TSDC peaks of aged PBT at different temperatures for different times revealed a reduction in their intensities and their shift towards higher temperatures when the aging becomes significant. This result can be explained by the diminution of molecular chain mobility, which is directly related to the area under the peak representing the polarization of the sample. This result was confirmed by DSC measurements, which revealed the growth and the shift of the peak, which is superimposed on the jump of the heat capacity, located around 38°C and characteristic of the glass transition, towards higher temperatures where aging becomes significant.

Universal local strain in solid-state amorphization: The atomic size effect in binary alloys

The atomic size effect in binary alloy systems during solid-state amorphization by particle irradiation is studied using molecular dynamics simulations. The critical dosage of irradiation for amorphization is decreased by increasing the atomic size mismatch or the solute concentration. The analysis of the atomic level strain shows that that the atomic-level strain distribution depends on the atomic species in the crystalline lattice, while it is almost the same in all glass systems. Amorphization occurs when the atomic-level strain reaches the universal critical value, which is independent of packing fraction, density, concentration and atomic size ratio. The nature of the universal strain is discussed in relation to the glass transition phenomenon.

Relaxations in relation to Liquid Crystalline Formation and Glass Transition for Comb-like Polymer: Structural Relaxation as expressed by Entropy Model and Activation Energy Spectrum

This study demonstrates that the modelling approach for the kinetic phenomenon of glass transition is effective to examine the relaxation. In the enthalpy relaxation of poly(cyanobiphenyl-yloxy) alkyl acrylate, the decrease in enthalpy was measured as a function of ageing time and ageing temperature. Obtained data was analysed at first with the activation energy spectrum (AES) model, and next, with the framework of the entropy model which follows the evolution of the configurational entropy of the sample during the whole thermal history in the experiment. The prediction of DSC curve based on the result of analysis for the glass transition will be presented. AES model gives information about thermally activated processes which are available to contribute to observed enthalpy changes against the thermal history. The activated processes are relevant to the rearrangement of molecules. The rearrangement corresponds to the structural changes of polymer chain which can be observed in our study as the change in optical texture, known as the coarsening dynamics of nematic domain for the liquid crystalline materials. The analysis for the coarsening is also shown to elucidate the specific feature of physical parameter.DOI: http://dx.doi.org/10.3126/jncs.v30i0.9377Journal of Nepal Chemical Society Vol. 30, 2012 Page: 107-110 Uploaded date: 12/19/2013

Study of glass transition phenomena in the supercooled liquid phase of methocarbamol, acetaminophen and mephenesin

We studied the thermochemical behaviour of five commonly used drugs namely naproxen, atenolol, methocarbamol (ML), acetaminophen and mephenesin (MP) using dielectric spectroscopy (10−3Hz–1MHz) and differential scanning calorimeter (DSC) down to liquid nitrogen temperature. The first two samples quickly crystallize during cooling, and we are able to study the glass transition phenomena in the latter three drugs only. The dielectric spectroscopy of the supercooled liquids of the latter three sample reveals the glass transition process as a pronounced relaxation process identifiable with so called primary relaxation process, or α-process, which is non-Debye in nature, and can be described well using Hevriliak–Negami (HN) equation. One sub-Tg process much smaller in magnitude is found in temperature range of 150K–250K that is arrhenius in its temperature dependence, which does not appear to be inter-molecular in nature.

Phase- and glass-transition phenomena due to the same configurational order–disorder mechanism in crystalline racemic sec-butylcyclohexane

We report molar heat capacities for racemic sec-butylcyclohexane (s-BCH) measured by the adiabatic calorimetric method within the temperature range from 14 to 200 K. In the crystalline state, we identified the presence of a second-order phase transition and a glass transition phenomenon, both originating from the same configurational degree of freedom. The phase and glass transition temperatures Ttrs and Tg were determined to be (136.7 ± 1.0) and (100 ± 1) K, respectively. The entropy of phase transition was estimated to be ΔtrsSm = 1.4 J K−1 mol−1 ≈ (1/4) R ln 2. The phase transition was judged to be of an order–disorder type on the basis of the fact that the glass transition occurred in the low-temperature heat-capacity tail. The entropy was interpreted to suggest that four molecules in the crystalline state constitute a unit for producing two distinct configurations in the coexistence of (d)- and (l)-s-BCH.

The activation energy and fragility index of the glass transition in Se76Te21Sb3 chalcogenide glass

The dynamics of the glass transition in Se76Te21Sb3 chalcogenide glass was studied under non-isothermal measurements using differential scanning calorimetry (DSC). The experimental result of the kinetic glass transition phenomenon, at different heating rates (5–40K/min), was analyzed on the basis of the relaxation process occurring in the transition temperature range. The activation energy of the glass transition was determined using an advanced isoconversion kinetic methods as well as from the heating rate dependence of the glass transition temperature. The fragility index m of the glass was estimated from the measurements of the activation energy of the relaxation process, which characterizes the glass transition. Moreover, the isoconversional kinetic analysis of the experimental data show that the activation energy of glass transition process is varying with the degree of transformation (and hence with temperature) from the glassy to the super cooled phase.

Ascorbic acid degradation of papaya during drying: Effect of process conditions and glass transition phenomenon

The aim of the present work was to study the degradation of ascorbic acid during hot air drying of papaya cubes and to verify its relationship with glass transition. A convective tray dryer was used in the drying experiments, which were carried out at air temperatures (Tair) of 40, 50, 60 and 70°C and air velocities of 1.0 and 1.32m/s. The lowest Tair induced higher retention of this nutrient at end of drying. At 70°C, papaya sample remained in the rubbery state until the end of drying, since product temperature (Tp) was above the glass transition temperature (Tg) along the process. This state is characterized by great molecular mobility inside the food, which facilitates the degradation. At 40°C, the rate of nutrient degradation was very slow as Tg was close to Tp and papaya has suffered phase transition from rubbery to glassy state.

Reorientational dynamics in molecular liquids as revealed by dynamic light scattering: From boiling point to glass transition temperature

We determine the reorientational correlation time τ of a series of molecular liquids by performing depolarized light scattering experiments (double monochromator, Fabry-Perot interferometry, and photon correlation spectroscopy). Correlation times in the range 10(-12) s-100 s are compiled, i.e., the full temperature interval between the boiling point and the glass transition temperature T(g) is covered. We focus on low-T(g) liquids for which the high-temperature limit τ ≅ 10(-12) s is easily accessed by standard spectroscopic equipment (up to 440 K). Regarding the temperature dependence three interpolation formulae of τ(T) with three parameters each are tested: (i) Vogel-Fulcher-Tammann equation, (ii) the approach recently discussed by Mauro et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 19780 (2009)], and (iii) our approach decomposing the activation energy E(T) in a constant high temperature value E∞ and a "cooperative part" E(coop)(T) depending exponentially on temperature [Schmidtke et al., Phys. Rev. E 86, 041507 (2012)]. On the basis of the present data, approaches (i) and (ii) are insufficient as they do not provide the correct crossover to the high-temperature Arrhenius law clearly identified in the experimental data while approach (iii) reproduces the salient features of τ(T). It allows to discuss the temperature dependence of the liquid's dynamics in terms of a E(coop)(T)/E∞ vs. T/E∞ plot and suggests that E∞ controls the energy scale of the glass transition phenomenon.