State diagram is used to determine the stability of dried and frozen foods during their processing and storage. In this study, state diagram of sardine was developed by measuring the freezing curve, ...glass line, solids melting line, and maximal-freeze-concentration conditions. Glass transition temperature decreased with the increase in water content and it was adjusted using a modified Gordon-Taylor equation. The glass transition of dry-solids and critical temperature were 184.1 and 12.5oC, and the model parameter of the modified Gordon-Taylor equation was estimated as 4.2, respectively. Solids melting temperature was modeled by Flory-Huggins equation; and dry-solids melting temperature and Flory-Huggins solids-water interaction parameter were determined as 199.4oC and 0.956, respectively. Freezing point of fresh sardine was observed as −1.3oC with ice melting enthalpy of 186.3 kJ/kg, and it decreased with the increase of solids due to the freezing point depression with solutes. Freezing point was adjusted by Chen equation based on Clausius-Clapeyron equation. The ultimate maximal-freeze-concentration temperatures, (Tm′)u and (Tg′′′)u were determined as −18.6 and −25.1oC, respectively and maximal-freeze-concentration solids were estimated as 0.90 g solids/g sample (i.e. un-freezable water 0.10 g water/g sample). This indicated that frozen sardines could be most stable if stored below −25.1oC, and dried fish stored below its glass transition.
•Glass transition of dry-solids was observed as 184.1oC and modified Gordon-Taylor parameter was 4.2 with critical temperature of 12.5oC.•Dry-solids melting-decomposition temperature and Flory-Huggins solids-water interaction were199.4oC and 0.956, respectively.•Freezing point of fresh sardine was observed as −1.3oC with ice melting enthalpy of 186.3 kJ/kg.•Ultimate maximal-freeze-concentration temperatures were determined as −18.6 and −25.1oC, respectively.•Un-freezable water was determined as 0.10 g water/g sample.
Predicting the glass-transition temperatures (Tg) of glass-forming polymers is of critical importance as it governs the thermophysical properties of polymeric materials. The cheminformatics ...approaches based on machine learning algorithms are becoming very useful in predicting the quantitative relationships between key molecular descriptors and various physical properties of materials. In this work, we developed a modeling framework by integrating the cheminformatics approach and coarse-grained molecular dynamics (CG-MD) simulations to predict Tg of a diverse set of polymers. The developed machine learning-based QSPR model identified the most prominent molecular descriptors influencing the Tg of a hundred of polymers. Informed by the QSPR model, CG-MD simulations are performed to further delineate mechanistic interpretation and systematic dependence of these influential molecular features on Tg by investigating three major CG model parameters, namely the cohesive interaction, chain stiffness, and grafting density. The CG-MD simulations reveal that the higher intermolecular interaction and chain stiffness increase the Tg of CG polymers, where their relative influences are coupled with the existence of side chains grafted on the backbone. This synergistic modeling framework provides valuable insights into the roles of key molecular features influencing the Tg of polymers, paving the way to establishing a materials-by-design framework for polymeric materials via molecular engineering.
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•A novel modeling framework was developed by integrating cheminformatics and coarse-grained molecular dynamics to predict the Tg of polymers.•The molecular features from machine learning model are grouped into three MD parameters - cohesive energy, chain stiffness, and grafting density.•The coarse-grained MD complements the machine learning model for a mechanistic and systematic interpretation of key molecular features.•The mutual and competing influence of cohesive energy vs. chain stiffness and grafting density on Tg is analyzed using coarse-grained MD
•Addresses confusion which seems to exist within the CHalcogenide Glass (ChG) community concerning the property known as the Glass Transition Temperature (Tg) and how to measure it accurately using ...Differential Scanning Calorimetry (DSC) instrumentation and experimental techniques.•Reviews the Moynihan and Kissinger mathematical models for the activation energy of glass transition, which have been used by the amorphous materials community for more than 55 years.•Introduces the unreported problems associated with each of these models, corrects the problems with detailed explanation and mathematical proofs and subsequently provides new models and general equations for future use.•Explains why Moynihan's model yields energy values which are significantly higher than Kissinger's model and provides a simple equation which relates the activation energy employed in the two models.•Demonstrates the use of the author's corrected models and equations for activation energy of glass transition by applying them to a representative ChG family of glasses.•Provides a model and equation for use by all researchers who seek to measure the ‘true’ glass transition temperature (Tg) of an amorphous material via DSC measurement.•Demonstrates the use of the author's new model and equation for determining the ‘true’ glass transition temperature (Tg) by applying it to a representative ChG family of glasses.•Provides a detailed interpretation of why a glass transition temperature measurement made by DSC instrumentation techniques introduces unique challenges, by introducing the Tool, Narayanaswamy and Moynihan MP function model (TNM model) and applying it to the rigors of a ChG measurement.
The glass transition temperature, Tg, is one of the most important physical attributes of glass in general and optical glasses in particular. Issues associated with refractive index stability, Modulation Transfer Function and upper use temperature of a lens system rely heavily on correct knowledge of Tg. While most oxide glass researchers and engineers understand the scientific meaning and application of Tg, confusion seems to exist within the chalcogenide glass community. This paper reviews the development history of theoretical models employed in determining the glass transition temperature and activation energy of transition for infrared chalcogenide optical glasses. It introduces corrections to these models to improve the fidelity and applicability of the equations used by many researchers. Our new models and equations are demonstrated through practical examples applied to a recently developed chalcogenide glass family. We believe that our models may also be used by oxide, halide and polymer glass scientists who employ DSC data.
For decades, scientists have debated whether supercooled liquids stop flowing below a glass transition temperature T
g0 or whether motion continues to slow gradually down to zero temperature. ...Answering this question is challenging because human time scales set a limit on the largest measurable viscosity, and available data are equally well fit to models with opposite conclusions. Here, we use short simulations to determine the nonequilibrium shear response of a typical glass-former, squalane. Fits of the data to an Eyring model allow us to extrapolate predictions for the equilibrium Newtonian viscosity ηN over a range of pressures and temperatures that change ηN by 25 orders of magnitude. The results agree with the unusually large set of equilibrium and nonequilibrium experiments on squalane and extend them to higher ηN. Studies at different pressures and temperatures are inconsistent with a diverging viscosity at finite temperature. At all pressures, the predicted viscosity becomes Arrhenius with a single temperature-independent activation barrier at low temperatures and high viscosities (ηN >10³ Pa·s). Possible experimental tests of our results are outlined.
A set of novel potassium‐calcium‐aluminosilicate glasses are developed to serve as the cladding material for a doped ZnSe core infrared fiber laser. The compositions exhibit high glass transition ...temperatures between 753°C and 918°C and high thermal expansion coefficients between 5.75 ppm/°C and 8.21 ppm/°C. We demonstrate successful application of these glass compositions as a cladding for a ZnSe tunable fiber laser.
In this article, polymer nanocomposites of polyisoprene with specific blend ratio 25/75 wt% of cis‐polyisoprene (CPI) and trans‐polyisoprene (TPI) with varying concentration (0.1, 1, and 5 wt%) of so ...synthesized silver nanoparticles (AgNPs) have been prepared and characterized through x‐ray diffraction, transmission electron microscope and scanning electron microscope. Experimental results on dynamic mechanical analysis show that addition of AgNPs to CPI/TPI blend reduces storage modulus, activation energy and fragility while enhances damping, however, glass transition temperature remains unaffected. Other mechanical properties such as toughness and tensile strength first increases on addition of AgNPs in the CPI/TPI blend, but a decrease is noticed on further increase of AgNPs concentration. Young's modulus shows a drastic decrease on addition of AgNPs into CPI/TPI blend, however, an increase is observed at higher concentration of AgNPs. Thermal analysis results show that thermal conductivity enhances with the enhancement in concentration of AgNPs into CPI/TPI blend.
Highlights
Addition of AgNPs into CPI/TPI blend reduces storage modulus, activation energy and fragility
Incorporation of AgNPs into CPI/TPI blend enhances damping but does not change glass transition temperature.
Increase in concentration of AgNPs in CPI/TPI blend increases the thermal conductivity.
In this article, polymer nanocomposites of CPI/TPI specific blend with AgNPs have been prepared and characterized through DMA and TCA.
Cooperative strings and glassy interfaces Salez, Thomas; Justin Salez; Kari Dalnoki-Veress ...
Proceedings of the National Academy of Sciences - PNAS,
07/2015, Letnik:
112, Številka:
27
Journal Article
Recenzirano
Odprti dostop
We introduce a minimal theory of glass formation based on the ideas of molecular crowding and resultant string-like cooperative rearrangement, and address the effects of free interfaces. In the bulk ...case, we obtain a scaling expression for the number of particles taking part in cooperative strings, and we recover the AdamâGibbs description of glassy dynamics. Then, by including thermal dilatation, the VogelâFulcherâTammann relation is derived. Moreover, the random and string-like characters of the cooperative rearrangement allow us to predict a temperature-dependent expression for the cooperative length ξ of bulk relaxation. Finally, we explore the influence of sample boundaries when the system size becomes comparable to ξ . The theory is in agreement with measurements of the glass-transition temperature of thin polymer films, and allows quantification of the temperature-dependent thickness h â of the interfacial mobile layer.
Molecular, polymeric, colloidal, and other classes of liquids can exhibit very large, spatially heterogeneous alterations of their dynamics and glass transition temperature when confined to nanoscale ...domains. Considerable progress has been made in understanding the related problem of near-interface relaxation and diffusion in thick films. However, the origin of "nanoconfinement effects" on the glassy dynamics of thin films, where gradients from different interfaces interact and genuine collective finite size effects may emerge, remains a longstanding open question. Here, we combine molecular dynamics simulations, probing 5 decades of relaxation, and the Elastically Cooperative Nonlinear Langevin Equation (ECNLE) theory, addressing 14 decades in timescale, to establish a microscopic and mechanistic understanding of the key features of altered dynamics in freestanding films spanning the full range from ultrathin to thick films. Simulations and theory are in qualitative and near-quantitative agreement without use of any adjustable parameters. For films of intermediate thickness, the dynamical behavior is well predicted to leading order using a simple linear superposition of thick-film exponential barrier gradients, including a remarkable suppression and flattening of various dynamical gradients in thin films. However, in sufficiently thin films the superposition approximation breaks down due to the emergence of genuine finite size confinement effects. ECNLE theory extended to treat thin films captures the phenomenology found in simulation, without invocation of any critical-like phenomena, on the basis of interface-nucleated gradients of local caging constraints, combined with interfacial and finite size-induced alterations of the collective elastic component of the structural relaxation process.
Self-healing polymeric materials Yang, Ying; Urban, Marek W
Chemical Society reviews,
2013-Sep-07, Letnik:
42, Številka:
17
Journal Article
Recenzirano
Inspired by nature, self-healing materials represent the forefront of recent developments in materials chemistry and engineering. This review outlines the recent advances in the field of self-healing ...polymers. The first part discusses thermodynamic requirements for self-healing networks in the context of conformation changes that contribute to the Gibbs free energy. The chain flexibility significantly contributes to the entropy changes, whereas the heat of reaction and the external energy input are the main contributors to enthalpy changes. The second part focuses on chemical reactions that lead to self-healing, and the primary classes are the covalent bonding, supramolecular assemblies, ionic interactions, chemo-mechanical self-healing, and shape memory polymers. The third part outlines recent advances using encapsulation, remote self-healing and the role of shape memory polymers. Recent developments in the field of self-healing polymers undeniably indicate that the main challenge will be the designing of high glass transition (
T
g
) functional materials, which also exhibit stimuli-responsive attributes. Build-in controllable hierarchical heterogeneousness at various length scales capable of remote self-healing by physical and chemical responses will be essential in designing future materials of the 21st century.
Last decade has witnessed the development of materials that exhibit stimuli-responsive attributes. Driven by scientific interests and technological needs this emerging field has generated a number of high impact sub-topics among which self-healing is particularly fascinating. This review discusses recent advances in thermodynamics, chemical reactions, and chemo-mechanical processes governing self-healing of polymeric materials.
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