Amorphous Polymers Research Articles

Regulation of Glass Transition Temperature in Thermo‐Responsive Epoxy Shape Memory Polymers: The Roles of Chemical Crosslinking Density and Chain Flexibility

ABSTRACTShape memory polymers (SMPs) are novel kinds of smart materials whose shape can be changed in external conditions such as heat stimulus. Due to their excellent structural versatility and high elastic strain, they have important applications in the field of biomaterials. Here, a series of amorphous shape memory polymer materials are prepared and their shape memory properties and glass transition temperature (Tg) are also investigated. A special kind of epoxy polymer, whose shape can be changed at around physiological temperature, is synthesized by regulating the crosslinking density and introducing flexible aliphatic epoxy chains. The shape memory function of this epoxy polymer is studied by deformation test. In addition, to explore their application in the field of biomedical materials, the biocompatibility of the materials are evaluated, including the effects on the erythrocyte hemolysis rate and cell activity. The experimental results show that this kind of epoxy polymer has good shape memory function and biocompatibility.

Insight into the “synergistic-relaxation effects” in amorphous polymer: Thermodynamic modeling, multiphysics simulation and application in 4D printing

Insight into the “synergistic-relaxation effects” in amorphous polymer: Thermodynamic modeling, multiphysics simulation and application in 4D printing

The Logistic Function in Glass Transition Models of Amorphous Polymers: A Theoretical Framework for Isobaric Cooling Processes

The Logistic Function in Glass Transition Models of Amorphous Polymers: A Theoretical Framework for Isobaric Cooling Processes

Polymer microparticles with ultralong room-temperature phosphorescence for visual and quantitative detection of oxygen through phosphorescence image and lifetime analysis

Room-temperature phosphorescence (RTP) materials exhibiting long emission lifetimes have gained increasing attention owing to their potential applications in encryption, anti-counterfeiting, and sensing. However, most polymers exhibit a short RTP lifetime (<1 s) because of their unstable triplet excitons. Herein, a new strategy of polymer chain stabilized phosphorescence (PCSP), which yields a new kind of RTP polymers with an ultralong lifetime and a sensitive oxygen response, has been reported. The rigid polymer chains of poly(methyl mathacrylate) (PMMA) immobilize the emitter molecules through multiple interactions between them, giving rise to efficient RTP. Meanwhile, the loosely-packed amorphous polymer chains allow oxygen to diffuse inside, endowing the doped polymers with oxygen sensitivity. Flexible and transparent polymer films exhibited an impressive ultralong RTP lifetime of 2.57 s at room temperature in vacuum, which was among the best performance of PMMA. Intriguingly, their RTP was rapidly quenched in the presence of oxygen. Furthermore, RTP microparticles with a diameter of 1.63 μm were synthesized using in situ dispersion polymerization technique. Finally, oxygen sensors for quick, visual, and quantitative oxygen detection were developed based on the RTP microparticles through phosphorescence lifetime and image analysis. With distinctive advantages such as an ultralong lifetime, oxygen sensitivity, ease of fabrication, and cost-effectiveness, PCSP opens a new avenue to sensitive materials for oxygen detection.

High‐precision numerical simulation method for thermal–mechanical coupling in rubbers

AbstractImproving the precision of numerical simulations in thermal–mechanical coupling for amorphous polymer materials is crucial for their effective utilization. To enhance the precision of rubber numerical simulations, this study proposed a method considering the temperature and strain rate to establish tensile testing conditions based on the principle of time–temperature equivalence. Additionally, to obtain more precise parameters for hyperelastic constitutive equations, stress relaxation experiments were conducted to determine a set of stress values under complete rubber stress relaxation, which were used to fit the hyperelastic components of the hyper‐viscoelastic algorithm. A finite element model of rubber rebound was established, and a hyperelastic model based on loss factor and a hyperelastic model based on Prony series (hyper‐viscoelastic) were used to calculate the temperature changes caused by rubber rebound coefficient and energy dissipation during the rebound process at 110, 120, and 130°C. We compared the calculation results of these two algorithms with experimental data to verify their accuracy. The research results show that the average error of the rebound coefficient of the hyperelastic algorithm at three temperatures is 3.63%, and the average error of the rebound coefficient of the hyper‐viscoelastic algorithm at these three temperatures is 0.93%. The comparison with the rebound test results shows that the hyper‐viscoelastic method is more accurate and better captures the viscoelastic hysteresis of rubber, but the model calculation time is longer. In addition, at the moment of rebound sample impact, the maximum temperature rise amplitude of the hyperelastic algorithm sample impact position is 2.60, 1.75, and 0.91°C, which are 110, 120, and 130°C, respectively; The maximum heating amplitudes of the hyper‐viscoelastic algorithm are 2.05, 1.35, and 0.61°C. The hyper‐viscoelastic algorithm is closer to the actual test results.Highlights Applied the principle of time–temperature equivalence. Determination of material parameters using the hyper‐viscoelastic algorithm. Calculated the temperature change during the rubber rebound process.

The Influence of Selected Parameters of Recycled Polyvinyl Butyral on the Sustainable Filament Extrusion Process

In recent years, sustainability has permeated nearly every aspect of our lives, and the manufacturing sector is no exception. The terms “sustainable manufacturing” and “zero-waste manufacturing” are now part of our everyday vocabulary. This study, which explores the influence of key parameters on the filament extrusion process using recycled polyvinyl butyral (PVB), which is an amorphous polymer commonly obtained from the glass recycling industry, has significant practical implications. By determining the optimal conditions for the extrusion process, we can enhance the mechanical properties of the produced PVB filament yarns and their printability. As a result of identifying errors, optimizing the process, and eliminating the resulting shortcomings, a fiber made of PVB material with a diameter of 1.75 mm (±0.06 mm) was created that can be used in most FDM devices. The length of the created fiber was approx. 20 m, and in the presentation of the results, it will be used for printing samples, adhesion tests to the printing mat, shrinkage tests, and tensile tests of the fiber. After removing all the shortcomings, the ideal extrusion temperature was at 155 °C. This temperature was verified using microscopic cross-sections, and deformations or changes were observed in their cross-sections. The deviation of the material currently undergoing testing for the adhesion of PVB to various types of print beds, which was found suitable for use in FFF devices, was 1.75 −0.25/+0.25. This, in turn, can significantly expand the application of these materials in additive manufacturing, thereby making a substantial contribution to the advancement of sustainable manufacturing.

Insights into the Thermal Expansion of Amorphous Polymers.

We investigated the thermal expansion of amorphous polystyrene (PS) and poly(methyl methacrylate) (PMMA) homopolymers using the temperature dependence of spatial electron-density correlations. The strong and broad X-ray interference maxima arising from inter- and intramolecular correlation distances were distinct, maintaining their shape during the heating of the samples to 250 °C. Three maxima characteristic of electron density correlations between the backbones, substituents along the chain, and repeat-units were observed. A remarkable temperature dependence was identified in the largest correlation distances arising from the intermolecular interactions. Based on the temperature dependence of the correlation distances, the coefficients of molecular expansion were very close to the coefficients of thermal expansion. This study provides a simple yet accurate way to correlate macroscopic volume expansions with the molecular expansion obtained from wide-angle X-ray scattering (WAXS) data.

Positional Isomerism Toward Tunable Organic Afterglow and Reversible Photoactivation Behavior for Anti‐Counterfeiting and Encryption

AbstractAchieving amorphous polymers with ultralong room‐temperature phosphorescence (RTP), tunable organic afterglow, and reversible photoactivation behavior is highly desirable for practical applications but challenging. Herein, simple positional isomers with three carboxyl groups located in the ortho, meta, and para positions of the triphenylamine skeleton are designed and synthesized. By physically blending with the poly(vinyl alcohol) matrix, these isomers show ultralong RTP properties, among which the meta‐isomer has the longest RTP lifetime (620.1 ms). Theoretical calculations reveal that the more efficient intersystem crossing, the slower radiative decay rate of the lowest triplet excitons, and stronger intermolecular hydrogen‐bonding interactions should be responsible for the superior RTP property of meta‐isomer. Furthermore, the tunable organic afterglow is readily realized via a triplet‐to‐singlet energy transfer process. More impressively, the meta and para isomers exhibit reversible photoactivated ultralong RTP properties after embedding into the rigid poly(methyl methacrylate) matrix. Finally, amorphous and flexible polymer films prepared from these positional isomers show potential applications in advanced anti‐counterfeiting and multilevel encryption through subtly combining ultralong RTP lifetime, tunable organic afterglow, and reversible photoactivation behavior.

Thermal Conductivity of Polymers: A Simple Matter Where Complexity Matters.

Thermal conductivity coefficient κ measures the ability of a material to conduct a heat current. In particular, κ is an important property that often dictates the usefulness of a material over a wide range of environmental conditions. For example, while a low κ is desirable for the thermoelectric applications, a large κ is needed when a material is used under the high temperature conditions. These materials range from common crystals to commodity amorphous polymers. The latter is of particular importance because of their use in designing light weight high performance functional materials. In this context, however, one of the major limitations of the amorphous polymers is their low κ, reaching a maximum value of ≈0.4 W/Km that is 2-3 orders of magnitude smaller than the standard crystals. Moreover, when energy is predominantly transferred through the bonded connections, κ ⩾ 100 W/Km. Recently, extensive efforts have been devoted to attain a tunability in κ via macromolecular engineering. In this work, an overview of the recent results on the κ behavior in polymers and polymeric solids is presented. In particular, computational and theoretical results are discussed within the context of complimentary experiments. Future directions are also highlighted.

Importance of Experiments That Can Test Theories Critically.

General dynamic and thermodynamic properties of complex materials, including amorphous polymers and molecular glass-formers, have been established from the wealth of experimental data accumulated over the years. Naturally, these general properties attract researchers to construct theories and models to address and explain them. Often more than one theory with contrasting or even conflicting theoretical bases can equally explain a general property rather well. The correct explanation becomes unclear, and progress is stopped. The resolution of the problem comes when an innovative experiment is performed with insightful results that can critically test the premise and assumptions of each theory. This important role played by experimentalists is exemplified by the contributions of Mark Ediger in several general properties considered in this paper: (1) dynamics of the components in binary polymer blends; (2) breakdown of the Stokes-Einstein and the Debye-Stokes-Einstein relations; (3) enhancement of surface mobility and in relation to formation of ultrastable glasses; and (4) the Johari-Goldstein β-relaxation in ultrastable glasses. Different theories proposed to explain these properties are discussed, including the Coupling Model of the author.

Mechanically Interlocked Macrocycles on Covalent Networks for Energy and Environmental Applications.

Macrocycles' unique properties of interacting with guest molecules have been an intriguing scientific endeavor for many decades. They are potentially practically useful for engineering applications, especially in energy and environmental applications. These applications are usually demanding, involving a high temperature, pH, voltage, etc., thus, finding suitable substrates that can endure working environments and sustain macrocycles' properties is highly desirable. In that sense, covalent networks are ideal as they are chemically/electrochemically/thermally stable and can be porous by design. Emerging porous materials, especially covalent organic frameworks (COFs), could be suitable as their porous spaces allow macrocycles to interact with guest species. In the past seven years, we have seen the rise of mechanically interlocked macrocycles on covalent networks (MIMc-CNs) that translate macrocycles' properties into macroscale materials. In this conceptual review, we first describe the idea of integrating MIMcs into COFs or conventional amorphous polymers. Next, we review the reported representative MIMc-CNs used in energy and environmental applications. We also provide a brief outlook for the future directions for the MIMc-CNs research.

Synthesis and characterization of non-porous amorphous polymers for enhanced iodine adsorption

Synthesis and characterization of non-porous amorphous polymers for enhanced iodine adsorption

Effect of CuF2 on Li+ transport in amorphous PEO-based solid polymer electrolytes

The limited Li+ transport capacity of poly(ethylene oxide) (PEO)-based solid polymer electrolytes restricts their practical applications. To enhance the Li+ diffusion coefficient, CuF2 was incorporated. Molecular dynamics simulations were performed on LiTFSI/PEO systems and CuF2/LiTFSI/PEO systems at varying lithium salt concentrations. The findings indicate that the inclusion of CuF2 in LiTFSI/PEO systems with high lithium salt concentration enhances the Li+ diffusion coefficient, whereas it diminishes at low lithium salt concentration. This phenomenon is attributed to the abundant coordination properties of Cu2+.

Hydrogen‐bond‐regulated mechanochemical synthesis of covalent organic frameworks: cocrystal precursor strategy for confined assembly

Two‐dimensional imine covalent organic frameworks (2D imine‐COFs) are crystalline porous materials with broad application prospects. Despite the efforts into their design and synthesis, the mechanisms of their formation are still not fully understood. Herein, a one‐pot two‐step mechanochemical cocrystal precursor synthetic strategy is developed for efficient construction of 2D imine‐COFs. The mechanistic investigation demonstrated that the cocrystal precursors of 4,4',4''‐(1,3,5‐triazine‐2,4,6‐triyl)trianiline (TAPT) and p‐toluenesulphonic acid (PTSA) sufficiently regulate the crystalline structure of COF. Evidenced by characterizations and theoretical studies, a helical hydrogen‐bond network was constructed by the N‐H···O supramolecular synthons between amine and sulfate in TAPT‐PTSA, demonstrating the role of cocrystals in promoting the organized stacking of interlayer π‐π interactions, layer arrangement, and interlayer spacing, thus facilitating the orderly assembly of COFs. Moreover, the protonation degree of TAPT amines, which tuned nucleophilic directionality, enabled the sequential progression of intra‐ and interlayer imine condensation reactions, inhibiting the formation of amorphous polymers. The transformation from cocrystal precursors to COFs was achieved through comprehensive control of hydrogen bond and covalent bond sites. This work significantly advances the concept of hydrogen‐bond‐regulated COF assembly and its mechanochemical method in the design and synthesis of 2D imine‐COFs, further elucidating the mechanistic aspects of their mechanochemical synthesis.

Hydrogen-Bond-Regulated Mechanochemical Synthesis of Covalent Organic Frameworks: Cocrystal Precursor Strategy for Confined Assembly.

Two-dimensional imine covalent organic frameworks (2D imine-COFs) are crystalline porous materials with broad application prospects. Despite the efforts into their design and synthesis, the mechanisms of their formation are still not fully understood. Herein, a one-pot two-step mechanochemical cocrystal precursor synthetic strategy is developed for efficient construction of 2D imine-COFs. The mechanistic investigation demonstrated that the cocrystal precursors of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (TAPT) and p-toluenesulphonic acid (PTSA) sufficiently regulate the crystalline structure of COF. Evidenced by characterizations and theoretical studies, a helical hydrogen-bond network was constructed by the N-H⋅⋅⋅O supramolecular synthons between amino and sulfonic groups in TAPT-PTSA, demonstrating the role of cocrystals in promoting the organized stacking of interlayer π-π interactions, layer arrangement, and interlayer spacing, thus facilitating the orderly assembly of COFs. Moreover, the protonation degree of TAPT amines, which tuned nucleophilic directionality, enabled the sequential progression of intra- and interlayer imine condensation reactions, inhibiting the formation of amorphous polymers. The transformation from cocrystal precursors to COFs was achieved through comprehensive control of hydrogen bond and covalent bond sites. This work significantly advances the concept of hydrogen-bond-regulated COF assembly and its mechanochemical method in the design and synthesis of 2D imine-COFs, further elucidating the mechanistic aspects of their mechanochemical synthesis.

Metal-phenolic network composites: from fundamentals to applications.

Composites with tailored compositions and functions have attracted widespread scientific and industrial interest. Metal-phenolic networks (MPNs), which are composed of phenolic ligands and metal ions, are amorphous adhesive coordination polymers that have been combined with various functional components to create composites with potential in chemistry, biology, and materials science. This review aims to provide a comprehensive summary of both fundamental knowledge and advancements in the field of MPN composites. The advantages of amorphous MPNs, over crystalline metal-organic frameworks, for fabricating composites are highlighted, including their mild synthesis, diverse interactions, and numerous intrinsic functionalities. The formation mechanisms and state-of-the-art synthesis strategies of MPN composites are summarized to guide their rational design. Subsequently, a detailed overview of the chemical interactions and structure-property relationships of composites based on different functional components (e.g., small molecules, polymers, biomacromolecules) is provided. Finally, perspectives are offered on the current challenges and future directions of MPN composites. This tutorial review is expected to serve as a fundamental guide for researchers in the field of metal-organic materials and to provide insights and avenues to enhance the performance of existing functional materials in applications across diverse fields.

TRANSPORT TECHNOLOGIES RELATED TO THE RESTORATION OF SHIP CARGO MECHANISMS WITH THE LATEST MODIFIED EPOXIES

The development of transport technologies today requires not only the creation of bases for the optimal technical use of vehicles, their technical operation, but also their maintenance and repair. One of the main tasks of transport technologies is the search for new promising scientific directions and their implementation in practice, as well as ensuring the effective use of the latest technologies and innovative methods for the construction or repair of water transport facilities. In this respect, the use of epoxy-based polymer composites is promising. They are characterised by improved adhesive and cohesive properties compared to other known oligomers, which determines the wide range of their application in water transport. In order to improve the properties of epoxy-based adhesives, additives of different physical nature are introduced into the epoxy matrix at the initial stage of moulding. This paper investigates the effect of the modifier d-ascorbic acid on the thermal properties of epoxies to obtain a material intended for the restoration of ship loading mechanisms. Based on the dynamics of heat resistance as a function of d-ascorbic acid concentration, the optimum content of the additive in the epoxy compound was determined, which is 1,25...1,50 pts.wt.for 100 pts.wt.of epoxy resin. The introduction of a modifier into the epoxy oligomer provides composites with the highest heat resistance values of all the materials studied. The heat resistance values increase from 341 K (for the epoxy matrix) to 352...354 K. The mechanism of increasing the heat resistance of an epoxy matrix in the presence of a modifier is substantiated, which involves the interaction of epoxy resin with an additive and a hardener as a result of chemical reactions. As a result of the reactions of structure formation of the compound based on epoxy oligomer and modifier in the presence of polyethylene polyamine, mainly strong chemical bonds of C-O, NH2, O-NH2, N=O, N-O-H, C=N type are formed, which largely determine the increase of cohesive strength of the newly formed modified epoxy matrices. It should be noted that it is the cohesive strength of the matrix that determines the thermal resistance of the material at elevated temperatures. It was found that the maximum glass transition temperature (333 K) was observed for the modified material containing d-ascorbic acid at 1,5 pts.wt. At this level of additive, the maximum values of both heat resistance and glass transition temperature were observed compared to the original epoxy matrix (327 K). At this modifier concentration, the cross-linking of the compound forms the most cross-linked structural network of an amorphous polymer with the highest number of chemical bonds.

Modelling of fracture-involved large strain behaviors of amorphous glassy polymers via a unified physically-based constitutive model coupled with phase field method

To promote the application of amorphous glassy polymers in structural components, a reliable prediction of the deformation and the potential fracturing behaviors is in demand. This work aims to provide a simple and feasible computational method to analyze the large strain behaviors, including elasticity, viscoplasticity, and the subsequent fracture, of amorphous glassy polymers. This is achieved by incorporating a physically-based constitutive model coupled with the fracture phase field method into the commercial finite element software Abaqus/Explicit. Inside the constitutive model, shear-yielding, crazing, and disentangling are considered as the underlying mechanisms for viscoplastic deformation and damage initiation. It is noteworthy that a unified craze-initiation criterion with a clear physical meaning is proposed, distinguishing this work from the previous in the literature. Moreover, a relatively user-friendly numerical implementation is suggested by exploiting the built-in features of Abaqus/Explicit. Taking the typical amorphous glassy polymers for example, i.e., polycarbonate (PC) and poly-methyl-methacrylate (PMMA), various experiments from the literature have been simulated. The proposed approach has been validated, since an acceptable agreement between the simulated and experimental results is realized.

An optical system for cellular mechanostimulation in 3D hydrogels

We introduce a method utilizing single laser-generated cavitation bubbles to stimulate cellular mechanotransduction in dermal fibroblasts embedded within 3D hydrogels. We demonstrate that fibroblasts embedded in either amorphous or fibrillar hydrogels engage in Ca2+ signaling following exposure to an impulsive mechanical stimulus provided by a single 250 µm diameter laser-generated cavitation bubble. We find that the spatial extent of the cellular signaling is larger for cells embedded within a fibrous collagen hydrogel as compared to those embedded within an amorphous polyvinyl alcohol polymer (SLO-PVA) hydrogel. Additionally, for fibroblasts embedded in collagen, we find an increased range of cellular mechanosensitivity for cells that are polarized relative to the radial axis as compared to the circumferential axis. By contrast, fibroblasts embedded within SLO-PVA did not display orientation-dependent mechanosensitivity. Fibroblasts embedded in hydrogels and cultured in calcium-free media did not show cavitation-induced mechanotransduction; implicating calcium signaling based on transmembrane Ca2+ transport. This study demonstrates the utility of single laser-generated cavitation bubbles to provide local non-invasive impulsive mechanical stimuli within 3D hydrogel tissue models with concurrent imaging using optical microscopy. Statement of significanceCurrently, there are limited methods for the non-invasive real-time assessment of cellular sensitivity to mechanical stimuli within 3D tissue scaffolds. We describe an original approach that utilizes a pulsed laser microbeam within a standard laser scanning microscope system to generate single cavitation bubbles to provide impulsive mechanostimulation to cells within 3D fibrillar and amorphous hydrogels. Using this technique, we measure the cellular mechanosensitivity of primary human dermal fibroblasts embedded in amorphous and fibrillar hydrogels, thereby providing a useful method to examine cellular mechanotransduction in 3D biomaterials. Moreover, the implementation of our method within a standard optical microscope makes it suitable for broad adoption by cellular mechanotransduction researchers and opens the possibility of high-throughput evaluation of biomaterials with respect to cellular mechanosignaling.

Application of the Thermal Analysis of Frozen Aqueous Solutions to Assess the Miscibility of Hyaluronic Acid and Polymers Used for Dissolving Microneedles.

Background: The combination of multiple polymers is anticipated to serve as a means to diversify the physical properties and functionalities of dissolving microneedles. The mixing state of components is considered as a crucial factor in determining their suitability. Objectives: The purpose of this study was to elucidate whether thermal analysis of frozen aqueous solutions can appropriately predict the miscibility of hyaluronic acid (HA) and other polymers used for dissolving microneedles prepared by a micromolding method. Methods: Aliquots of aqueous polymer solutions were applied for thermal analysis by heating the samples from -70 °C at 5 °C/min to obtain the transition temperature of amorphous polymers and/or the crystallization/melting peaks of polymers (e.g., polyethylene glycol (PEG)). Films and dissolving microneedles were prepared by air-drying of the aqueous polymer solutions to assess the polymer miscibility in the solids. Results: The frozen aqueous single-solute HA solutions exhibited a clear Tg' (the glass transition temperature of maximally freeze-concentrated solutes) at approximately -20 °C. The combination of HA with several polymers (e.g., dextran FP40, DEAE-dextran, dextran sulfate, and gelatin) showed a single Tg' transition at temperatures that shifted according to their mass ratio, which strongly suggested the mixing of the freeze-concentrated solutes. By contrast, the observation of two Tg' transitions in a scan strongly suggested the separation of HA and polyvinylpyrrolidone (PVP) or HA and polyacrylic acid (PAA) into different freeze-concentrated phases, each of which was rich in an amorphous polymer. The combination of HA and PEG exhibited the individual physical changes of the polymers. The polymer combinations that showed phase separation in the frozen solution formed opaque films and microneedles upon their preparation by air-drying. Coacervation occurring in certain polymer combinations was also suggested as a factor contributing to the formation of cloudy films. Conclusions: Freezing aqueous polymer solutions creates a highly concentrated polymer environment that mimics the matrix of dissolving microneedles prepared through air drying. This study demonstrated that thermal analysis of the frozen solution offers insights into the mixing state of condensed polymers, which can be useful for predicting the physical properties of microneedles.