We highlight certain key achievements in experimental work on molecular, colloidal and granular glassformers. This short review considers these three classes of experimental systems and focusses ...largely on the work of the authors and their coworkers and thus is far from exhaustive. Our goal is rather to discuss particular experimental results from these classes and to explore universality and specificity across the broad range of length– and time–scales they span. We emphasize that a variety of phenomena, not least dynamical heterogeneity, growing lengthscales and a change in structure, albeit subtle, are now well established in these three classes of glassformer. We then review some experimental measurements which depend more specifically on the class of glassformer, such as the Gardner transition and some which have been investigated more in one or two classes than in all, such as configurational entropy and evidence for a dynamical phase transition. We finally put forward some open questions and consider what could be done to fill some of the gaps between theoretical approaches and experiments.
Nous passons en revue certains des résultats expérimentaux importants concernant les systèmes vitrifiables moléculaires, colloïdaux et granulaires, sans prétendre aucunement à l’exhaustivité, mais en nous concentrant principalement sur nos propres travaux et ceux de nos collaborateurs. Notre objectif est de discuter les résultats expérimentaux pour chacun de ces systèmes en montrant à la fois ce qu’ils contiennent d’universel, malgré les grandes différences des échelles d’espace et de temps entre ces trois classes de matériaux, et ce qu’il y a de spécifique. Pour ce qui est des aspects universels, nous montrons en particulier que la notion d’hétérogénéité de la dynamique, celle de longueur de corrélation croissante, voire même celle de changement de structure subtil, sont désormais bien établies dans chacune des trois catégories de systèmes vitrifiables. Ensuite, nous passons en revue certains phénomènes expérimentaux qui dépendent plus spécifiquement de la catégorie de systèmes considérée, comme la transition de Gardner, et d’autres phénomènes qui ont été étudiés davantage dans une ou deux des catégories que dans l’ensemble des classes. Enfin, nous posons quelques questions ouvertes et examinons ce qui pourrait être fait pour combler certaines lacunes entre les approches théoriques et les expériences.
Organic solar cells (OSCs) are designed based on a blend of polymer donor and small molecular acceptor whereby the thermodynamic relaxation of the morphology raises the concerns related to ...operational stability. Herein, it is demonstrated that the classical Y6‐based binary device can be stabilized by using its derivative of ZCCF3 as the third component, which is designed with the replacing of the thiadiazole group on Y6 with the trifluoromethyl substituted diazepine unit. ZCCF3 delivers not only higher glass transition temperature (Tg) than Y6 but also have hyper‐miscibility with Y6, contributing to a favorable diffusion‐limited Y6:ZCCF3 alloy when blended with polymer donor. Consequently, a champion power conversion efficiency of 18.54% is achieved in the optimal PM6: Y6: ZCCF3 devices, which can retain their 80% initial efficiency of up to 360 h. This study highlights the importance of high Tg of the third component and its derived hyper‐miscible accepter alloys in achieving highly efficient and stable OSCs.
Herein, it is demonstrated that the classical Y6‐based binary device can be stabilized by using its derivative of ZCCF3 as the third component. The new acceptor delivers not only a higher glass transition temperature than Y6 but also have a hyper‐miscibility with Y6, contributing to a favorable diffusion‐limited Y6: ZCCF3 alloy when blended with polymer donor.
Relaxation theories of the glass transition and viscous flow of glass-forming melts are presented. The focus is on modern representations of the glass transition equation qτg = δTg that describes the ...appearance of a glassy state during cooling. Here, q = dT/dt is the temperature change rate during melt cooling and τg is the relaxation time at the glass transition temperature Tg. Various methods for calculating the characteristic temperature band δTg during the liquid-glass transition are considered. The generalized equation for the dependence of Tg on the melt cooling rate is derived. Based on the model of delocalized atoms, a modified kinetic glass transition criterion is discussed. A generalized viscosity equation for glass-forming liquids is derived.
From the perspective of rubber/glass transition, this study clarified that the impact of dextran on retarding hardening behavior and slowing starch retrogradation of Chinese Steamed Bread (CSB) ...depended on its molecular weight and concentration level. Guggenheim-Anderson-de Boer (GAB) model was fitted to explore critical behavior changes in rubber/glass transition of CSB. Incorporation of high molecular weight dextran enhanced the elasticity of dough and porosity of CSB, reduced the aging and hardening degree of CSB at appropriate addition levels. CSB hardness showed a growing tendency during storage, while macromolecular dextran reduced the hardness and retrogradation degree by 22.87 % and 67.53 %. Dextran with high molecular weights lowered the glass transition temperature (Tg) and improved the moisture sorption and molecular mobility of CSB under various relative humidity (RHs) conditions by providing hydrophilic sites or intermolecular space to bind water molecules. Meanwhile, it reinforced the binding between denatured gluten and gelatinized starch. Both of them devoted to starch retrogradation inhibition and stable quality maintenance of CSB. CSB is suggested to maintain stable quality at room temperature with RHs ≤33 % to prevent rubber/glass transition. This work provided theoretical guidance for fractionation application of dextran to regulate the quality and extend the shelf-life of flour products.
6,6′-(Propane-2,2-diyl)bis(3-(3-(diethoxy(methyl)-silyl)propyl)-3,4-dihydro-2H-benzoe1,3oxazine) (BA-mdes) monomers were thermally polymerized to form a polybenzoxazine network containing Ph-OH and ...Si-OEt groups, and then these groups further reacted to obtain Si–O–Ph bond additionally cross-linked organic–inorganic hybrid polybenzoxazine. The glass transition temperature (Tg, tan δ) of the resulting polybenzoxazine reaches ≈400 °C.
This paper reviews glass transition kinetics models that are developed to describe the formation of structural (for example, covalent and metallic) glasses, as well as to account for the transition ...of a polymer to a solid glassy state. As the two approaches most frequently used over the last decade to model the glass transition, the Tool-Narayanaswamy-Moynihan model and the Adam-Gibbs theory of glass transition are described together with examples of their applications. Also discussed are entropy-based approaches that rely on irreversible thermodynamics methods originated in the work of De Donder, Mandelstam, and Leontovich. The actual problems that arise in applying these methods and the prospects of their development are discussed. A brief overview of statistical glass transition models is given, including the mode-coupling and energy-landscape theories.
Conjugated polymers are emerging as promising building blocks for a broad range of modern applications including skin‐like electronics, wearable optoelectronics, and sensory technologies. In the past ...three decades, the optical and electronic properties of conjugated polymers have been extensively studied, while their thermomechanical properties, especially the glass transition phenomenon which fundamentally represents the polymer chain dynamics, have received much less attention. Currently, there is a lack of design rules that underpin the glass transition temperature of these semirigid conjugated polymers, putting a constraint on the rational polymer design for flexible stretchable devices and stable polymer glass that is needed for the devices’ long‐term morphology stability. In this review article, the glass transition phenomenon for polymers, glass transition theories, and characterization techniques are first discussed. Then previous studies on the glass transition phenomenon of conjugated polymers are reviewed and a few empirical design rules are proposed to fine‐tune the glass transition temperature for conjugated polymers. The review paper is finished with perspectives on future directions on studying the glass transition phenomena of conjugated polymers. The goal of this perspective is to draw attention to challenges and opportunities of controlling, predicting, and designing polymeric semiconductors, specifically to accommodate their end use.
This paper reviews the glass transition phenomenon of conjugated polymers. The glass transition temperature data for a broad range of conjugated polymers are compiled and discussed. Empirical design rules are proposed to guide the fine‐tuning of glass transition in conjugated polymers. The challenges and opportunities in understanding glass transition and connecting it to the end‐use performance are also discussed.
In this work we synthesized and studied a series of linear polylactides (PLA) with a fixed L/d -lactide stereoisomer ratio, covering together the wide range of molecular weights, Mn, from ∼6 to ...∼80 kg/mol. The basic aims are the segmental mobility mapping, in terms of time scale and fragility, the recording of the Mn dependences of the glass transition temperature and fragility, and, finally, the comparison with corresponding findings from the literature. Obviously, the direct Mn effects on Tg are assessed by preserving PLA at the amorphous state, i.e., via melting and relatively fast cooling. The segmental mobility is studied by conventional and temperature modulated calorimetry, whereas the molecular dynamics is assessed employing the technique of broadband dielectric spectroscopy in combination with proper critical analysis and evaluation routes. The calorimetric and dielectric Tg(Mn) trends were found consistent between each other as well as with previous findings in similar systems, both with respect to experimental findings and theoretic predictions for PLAs of similar L/D ratio. The Mn threshold of entanglements seems to lay between 13 and 28 kg/mol. The fragility index of the α relaxation, i.e., the dielectric analogue of the glass transition, exhibits a similar dependence to that of Tg(Mn). When decreasing Mn to very low values, the high fragility (∼150) drops down to 0 (Mñ6 kg/mol), denoting the vanishing of the polymer chains’ cooperativity. Qualitatively interesting alternations are recorded in the dielectric strength of the α relaxation and the relaxation times width. The effects are discussed in terms of the various parameters co-affecting the polymer dynamics, namely, chain lengths, free volume and dynamical heterogeneities.
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•Preparation and molecular dynamics investigation of linear PLA with from ∼6 to ∼80 kg/mol.•Recording of the Mn dependence of the calorimetric/dielectric Tg and of the fragility index of α relaxation.•The Mn threshold for entanglements is estimated between 13 and 28 kg/mol.•Consistent findings with previous experimental ones and theoretic predictions for PLAs of similar L/D ratio.
Polymers below their glass transition temperature (Tg) are non-equilibrium glasses because excess free volume “frozen” between kinetically-restricted polymer chains slowly relaxes over time towards ...equilibrium via local, segmental chain motion. This process, known as physical aging, is observed through time-dependent decreases in a polymer's specific volume, enthalpy, etc. This article focuses on the history of glassy polymers in membrane separation applications. Open questions regarding the influence of thickness (e.g., membrane geometry) and temperature on physical aging in glassy polymers are highlighted.
Glassy polymers have non-equilibrium excess free volume. Consequently, they typically have time- and history-dependent properties. For example, membrane gas permeance often gradually decreases with time. Display omitted
•A polymer below its glass transition temperature has non-equilibrium excess volume.•Glassy polymers have additional sorption capacity relative to rubbery polymers.•Non-equilibrium excess volume affects polymer properties (e.g., transport, optical).•The thickness- and temperature-dependences of physical aging remain open questions.•Glassy polymers are frequently applied in gas separation membrane applications.
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