Amorphous Polymers Research Articles

Effects of sodium chloride on mechanical properties in amorphous polymers of waterlogged archaeological wood: Insights from molecular dynamics simulations

Sodium chloride (NaCl) is the main soluble salt component of marine waterlogged archaeological wood, and it causes deterioration of wood fibres. In this study, a molecular dynamics simulation of three types of archaeological wood from the Quanzhou Song Shipwreck was employed to investigate the impact of NaCl on the mechanical properties of amorphous components consisting of amorphous cellulose, hemicellulose, and lignin. The findings revealed that water molecules bound to the fibres enhanced the mechanical performance of the woody fibres. However, NaCl affected the stability and mechanical properties of the amorphous components. By using molecular dynamics simulations, 24 sets of amorphous fibre models, consisting of fir, pine, and camphorwood with salt concentrations ranging from 0 % to 7 %, were constructed to further analyse the influence of salt content on the mechanical properties of the amorphous components. The results showed that all three species of archaeological wood exhibited similar trends, with the adsorption energy and radial distribution function between wood fibres and water molecules decreasing with increasing NaCl concentration, leading to the gradual rupture of hydrogen bonds in water molecules. Consequently, more water molecules engage in ion hydration, resulting in an increase in the amount of free water within the amorphous regions. This, in turn, degrades the mechanical properties of the amorphous components. This study contributes significantly to a comprehensive understanding of the mechanical properties of marine archaeological wood and is important for decision-making in studies related to the preservation and evaluation of marine waterlogged wooden artefacts.

Circularly Polarized Phosphorescence of Benzils Achieved by Chiral Supramolecular Polymerization

AbstractIn current approaches for circularly polarized phosphorescent materials, the crystallization of chiral phosphors suffers from poor processability, while integrating them into an amorphous polymer matrix results in unsatisfactory chiroptical signals due to the absence of chirality communication. Here, we have developed an innovative strategy through chiral supramolecular polymerization of benzil phosphors facilitated by intermolecular hydrogen bonds. The inherent film‐forming capabilities of non‐covalent supramolecular polymers obviate the need for an external polymer matrix. The pronounced helical asymmetry of benzil phosphors resulting from chiral supramolecular polymerization leads to enhanced circularly polarized phosphorescence compared to their non‐hydrogen‐bonded counterparts. The circularly polarized phosphorescent signals can be further modulated by varying the location of stereogenic centers or introducing halogen bonding to benzils. Incorporation of platinum(II) phosphor into the benzil supramolecular polymers induces both chirality and triplet‐to‐triplet energy transfer, leading to a change in circularly polarized phosphorescent color from yellow to red. In summary, chiral supramolecular polymerization of phosphors represents a novel and effective approach to circularly polarized phosphorescent materials.

Construct Amorphous Polymer Interface to Enhance the Thermoelectric Performance of Commercial Bi0.5Sb1.5Te3 Materials.

Interfaces, such as grain boundaries and phase boundaries in thermoelectric (TE) materials, play a crucial role in the carrier/phonon transport. Accurate control of the features of interfaces, including composition, crystalline nature, and thickness may give rise to a promising pathway to break the trade-off between phonon and carrier transport properties, which is essential to design high-performance TE materials. In this work, the amorphous polymer interface (API) layer is introduced to the p-type commercial Bi0.5Sb1.5Te3 (BST) TE material by the liquid-phase sintering process. Due to the larger mismatch in the acoustic impedance or phonon spectra between the amorphous polymer layer and the BST phase, the additional interfacial thermal resistance is introduced, which results in a large decrease in lattice thermal conductivity. It is found that the interfacial thermal resistance at the API is much higher than that of normal grain boundary and hetero interface reported in the literature. Conversely, taking advantage of the strong electron and phonon scattering, a large net get of ZT was achieved. A maximum ZT of ∼1.22 at 350 K was obtained in the BST/polyimide-0.5% sample, which is considerably greater than that of the commercial BST matrix (∼0.99 at 350 K). Furthermore, the optimized BST/polymer sample also exhibited almost 20% enhancement in hardness compared with the pure BST sample. This work has opened a new window for designing high-performance TE composites, which may extend to other material systems.

Compositional and Temperature Dependence of Amorphous Polymer Networks Undergoing Mechanotropic Phase Transitions

Compositional and Temperature Dependence of Amorphous Polymer Networks Undergoing Mechanotropic Phase Transitions

Experimental investigations of uniaxial and biaxial cold stretching within PC‐films and bars using optical measurements

AbstractPolycarbonate (PC) is an amorphous polymer that is an extremely robust material with a high tenacity, and thus suitable for a lightweight construction with glass‐like transparency. Due to these advantageous properties, PC is often used in industry for example in medical devices, automotive headlamps, sporting equipment, electronics, and a variety of other products. PC is often subjected to uniaxial and biaxial loading conditions. Therefore, reliable material models have to take into account the various resulting experimental effects. For those reasons, we investigate PC specimens under uniaxial and biaxial loading by using different stretch rates and loading scenarios. In addition to that, we propose methods for optical measurement of local stretches to obtain the approximated local true stress. In future work, the displacement fields and the resulting reaction forces will be used for parameter identification of constitutive equations.

Predicting the solubility of gases, vapors, and supercritical fluids in amorphous polymers from electron density using convolutional neural networks

A twin convolutional neural network is proposed to predict the pressure and temperature-dependent sorption of gases, vapors, and supercritical fluids in amorphous polymers, using spatial electron density distribution.

Low-entropy amorphous dielectric polymers for high-temperature capacitive energy storage

A short-range ordered, long-range disordered structure in a low-entropy amorphous polymer, with locally extended polymer chains, inhibits electron transport in dielectric polymers, enhancing capacitive performance at elevated temperatures.

Understanding stress relaxation behavior of amorphous polystyrene based on microstructural heterogeneity

The relationship between stress relaxation behavior and inherent microstructural heterogeneity in amorphous polystyrene materials is studied in this work. Starting from the basic Maxwell viscoelastic model and extending to the three-parameter stretched exponential equation, the nature of the distribution of characteristic timescales and the segmental effects during polymer stress relaxation are discussed. The results indicate that the stress relaxation behavior of amorphous polymers exhibits non-exponential characteristics. Neither a single characteristic time with exponential decay nor a finite spectrum method with finite characteristic time can adequately describe the stress relaxation behavior of polystyrene due to the continuous distribution of characteristic timescales resulting from microstructural heterogeneity in amorphous polymers. In addition, the changes in stress relaxation behavior caused by physical aging are explored. Aging leads to a transition of the system towards a more stable energy state, making it difficult to activate the relaxation of the individual units, thus slowing down the stress relaxation process and increasing the characteristic time.

Redox-active, photoluminescent porous polymers based on spirofluorene-bridged N-heterotriangulenes and their feasibility as organic cathode materials.

Novel microporous polymers were synthesized through Yamamoto polymerization of selectively brominated spirofluorene-bridged N-heterotriangulenes. Extensive characterization, including combustion analysis, ToF-SIMS, IR, and Raman spectroscopy, confirmed the elemental composition and integrity of the polymers. The amorphous polymers, observed by scanning electron microscopy as globular particles aggregating into larger structures, exhibited remarkable thermal stability (decomposition temperatures > 400 °C) and BET surface areas up to 690 m2 g-1. Dispersions of the tert-butyl-substituted polymer in different solvents displayed bathochromically shifted emission with remarkable solvatochromism. The polymer is reversibly oxidized at +3.81 V (vs. Li/Li+) in composite electrodes with carbon black and reaches specific capacities up to 26 mA h g-1 and excellent cycling stability when implemented as cathode material in lithium-ion batteries. Our results highlight the potential of spirofluorene-bridged N-heterotriangulenes as versatile building blocks for the development of functional redox-active porous polymers.

A Monte Carlo simulation of tracer diffusion in amorphous polymers.

Tracer diffusion in amorphous polymers is a sought-after quantity for a range of technological applications. In this regard, a quantitative description of the so-called decoupling from the reverse proportionality between viscosity and diffusion coefficient into a fractional one remains a challenge requiring a deeper insight. This work employs a Monte Carlo simulation framework in 3 dimensions to investigate the consequences of different scenarios for estimating this fractional exponent on the diffusion coefficient of tracers in polymers near glass transition. To this end, we adopted a continuous-time random walk model for tracer diffusion in the supercooled liquid state. The waiting time distribution of the diffusants was computed based on the rotational correlation times of the polymer. This proposed procedure is of particular interest because it brings the quantity of waiting time (and its statistics) in connection with the measurable observable of rotational times. In the framework of our simulations the aforementioned fractional exponent appears in the relation between the diffusant's waiting time and the rotational time of the diffusion medium. A limited comparison with experimental diffusivities from the literature revealed a reasonable agreement with a fractional exponent on the basis of the molar volumes of the diffusant and the monomeric unit. Finally, an analysis of time-averaged mean squared displacement pointed to normal Brownian dynamics for tracer diffusion in polymers above the glass transition temperature.

Evolution of free volume elements in amorphous polymers undergoing uniaxial deformation: a molecular dynamics simulations study

Amorphous polymers are considered promising materials for separation applications due to their excellent transport properties and low fabrication costs.

Dual photoresponsive & water-triggered nitric oxide releasing materials based on rhodium-based metal-organic polyhedra.

The exogenous administration of nitric oxide (NO) is considered a potential therapeutic treatment against a great variety of diseases due to its significant role in multiple physiological functions. Due to the gaseous nature, short lifetime and dose- and tissue-dependent activity of this molecule, the development of new administration procedures is required to control the NO delivery in terms of dosage, timing, and location. In this work, we propose a new molecular material based on robust metal-organic polyhedra (MOPs) for controlled NO release. We select dirhodium paddlewheel complex-based cuboctahedral MOPs (RhMOP), in which NO can chemically coordinate to the open-metal sites at the axial sites of dirhodium paddlewheel moieties. We further prepare amorphous coordination polymer particles (CPPs) by connecting RhMOP with bis(imidazole) linkers at the external axial sites. Both molecular MOPs and polymeric CPPs show relevant NO payloads and the release of NO can be triggered by two different stimuli: light and humidity. We show that imidazole ligands coordinating to the external axial sites of the paddlewheel moieties tune the light-triggered NO release property. We further demonstrate that the size and the extrinsic pores of CPPs are important for enhanced NO release.

Holographic fabrication of reconfigurable diffractive elements

The fabrication of Diffractive Optical Elements (DOEs) involves the analog patterning of material surfaces on the scale of light wavelength. This typically requires multi-step lithographic processes. Differently from the photoresists of standard lithography, thin films of amorphous azobenzene-containing polymers (azopolymers) can directly produce a structured surface using a single irradiation step with structured light. The resulting surface reliefs can be used directly as planar phase-modulating DOEs without the need for any post-exposure process. Additionally, the surface geometry and its optical functionality can be reconfigured at will. Here, we demonstrate reprogrammable and ready-to-use azopolymer diffractive gratings, lenses, and holographic projectors, produced by grayscale digital holographic patterns. By exploiting the all-optical scheme based of computer-generated holography, the diffraction behavior of the DOEs is optimized during the developing of structured surfaces. Full all-optical reconfigurability of the fabricated devices is also achieved. Our approach provides a versatile, efficient, and all-optical reversible fabrication framework for DOEs, making it a promising option to overcome the demanding, cumbersome, and irreversible fabrication processes typically involved in the realization of planar diffractive optical devices.

The route to achieve isotropy in 3D printing parts via Fused Filament Fabrication with Advanced Semicrystalline Thermoplastics

This review investigates the challenges of Additive Manufacturing using commodity, engineering, and advanced materials, both amorphous and semicrystalline. It explains the reasons behind the weaker mechanical performance of semicrystalline materials compared to amorphous polymers used in the 3D printing process. The performance of 3D printing is discussed to demonstrate the current position of additive manufacturing as one of the promising techniques meeting the requirements of the 5.0 Industrial Revolution, particularly in terms of delivering personalized products. The differences between amorphous and semicrystalline materials on a macromolecular level, including the strength of the single bond in the polymer backbone chain and the effect of electron donation to the backbone, are discussed. Interlayer imperfections are classified into several groups: moisture in the feedstock filament, inconsistent filament diameter, shrinkage of the deposited materials, and, most importantly, crystallization kinetics of semicrystalline materials. Finally, insights on how to achieve properties closer to an isotropic body when advanced semicrystalline materials are printed, in order to overcome layer-layer defects, are provided.

Random field reconstruction of three-phase polymer structures with anisotropy from 2D-small-angle scattering data.

In this paper we present a computational method to analyze 2-dimensional (2D) small-angle scattering data obtained from phase-separated soft materials and output three-dimensional (3D) real-space structures of the three types of domains/phases. Specifically, we use 2D small-angle X-ray scattering (SAXS) data obtained from hydrated NafionTM membranes and develop a workflow using random fields to build the 3D real-space structure comprised of amorphous hydrophilic domains, amorphous polymer domains, and crystalline polymer domains. We demonstrate the method works well by showing that the reconstructed 3D NafionTM structures have a computed scattering profile that matches the input experimental scattering profile. Though not demonstrated in this work, such reconstructions can be used for further analysis of domain shapes and sizes, as well as prediction of transport properties through the structure. Our method in this work extends capabilities beyond the previously published random field small angle scattering reconstruction method introduced by Berk [Phys. Rev. Lett. 1987, 58 (25), 2718-2721] that had been used to reconstruct structures from 1D small angle scattering data of two-phase systems. The method in this work can be used to generate isotropic, two-phase reconstructions, but can also handle 2D SAXS profiles from three-phase systems that have structural anisotropy resulting from material processing effects.

Therapeutic coordination polymers: tailoring drug release through metal-ligand interactions.

Developing tunable materials which exhibit sustained drug release is a considerable challenge. Herein, we report the concept of Therapeutic Coordination Polymers (TCPs); non-porous coordination polymers constructed from biocompatible components which demonstrate tunable zero-order drug release kinetics upon degradation of metal-ligand bonds. TCPs were constructed from three principal components: (i) a cationic metal center (M = Mg2+, Mn2+, Zn2+, or Cu2+); (ii) an anionic drug (Diclofenac); and (iii) an alkyl bis-imidazole organic ligand which behaves as a "linker" between metal centers. Most drug-release materials, such as amorphous polymer dispersions, or metal-organic frameworks rely on a diffusion-based mechanism for drug release, but the degradation-controlled release of drugs from non-porous one-periodic coordination polymers has been largely unexplored. TCPs described herein exhibit a high wt% of pharmaceutical (>62%), tailorable zero-order drug release rate kinetics which span over three orders of magnitude, and stimuli-responsive drug release behavior making them well suited for extended drug-release applications.

Mechanical Degradation and Fatigue Life of Amorphous Polymers

Due to favorable properties (cheap price, easy processing, preeminent combination of toughness and strength, clearness, recyclability etc.), amorphous polymers are widely used in windows, sporting goods, vehicles, aeronautic equipment, electronics, and health technology. However, their applications may suffer from fatigue, when material fails at significantly lower stress levels than under monotonic loading conditions; fatigue loads result in polymer degradation which can affect horrific accidents (e.g., the air disaster of China Airlines Flight 611) and tremendous financial losses. Despite this motivation, fatigue behavior of amorphous polymers has been scarcely investigated so far. In this study, micro-mechanical characteristics of amorphous structure and their influence on macroscopic deformation behavior (ratcheting) and fatigue life are investigated. It was found (SEM results) that polymer degradation is the process of failure (shear banding affecting micro-cracking and fracture) causing finally breakdown of polymer network. The degradation process was very rate sensitive, and the crack initiation phase before rapid rupture of the material encompassed the majority (even 95 %) of the total fatigue life. Certain fracture surfaces showed sharpened protrusions indicating that the separation of the fracture surfaces from each other occurred precisely on those protrusions. The vein-like, cellular, and rippled patterns of shear bands on fracture surfaces increased fracture toughness and thus, fatigue resistance and life.

Synthesizing a Water-Soluble Polymeric Nitrification Inhibitor with Novel Soil-Loosening Ability.

Nitrification inhibitor is essential for increasing the nitrogen utilization efficiency of agricultural plants, thus reducing environmental pollution and increasing crop yield. However, the easy volatilization and limited functional property is still the bottleneck of nitrification inhibitors. Herein, a novel water-soluble polymeric nitrification inhibitor was synthesized through the copolymerization of acrylamide and bio-based acrylic acid, which was synthesized from biomass-derived furfural, and the complexation of carboxyl groups and 3,4-dimethylpyrazole. The results showed that the nitrification inhibitor was an amorphous polymer product with a glass transition temperature of 146 °C and a thermal decomposition temperature of 176 °C, and the content of 3,4-dimethylpyrazole reached 2.81 wt%, which was 115% higher than our earlier product (1.31 wt%). The polymeric nitrification inhibitor can inhibit the activity of ammonia-oxidizing bacteria effectively, thus inhibiting the conversion of ammonium nitrogen to nitrate nitrogen and converting the insoluble phosphate into soluble and absorbable phosphate. By introducing a copolymer structure with a strong flocculation capacity, the polymeric nitrification inhibitor is further endowed with a soil-loosening function, which can increase the porosity of soil to improve the soil environment. Therefore, the nitrification inhibitor can be used in water-soluble and liquid fertilizers, as well as in high tower melting granulated compound fertilizers.

Mechanical Properties of 3D-Printed Liquid Crystalline Polymers with Low and High Melting Temperatures.

Additive manufacturing allows for the production of complex components using various types of materials such as plastics, metals and ceramics without the need for molding tools. In the field of high-performance polymers, semi-crystalline polymers such as polyetheretherketone (PEEK) or amorphous polymers such as polyetherimide (PEI) are already successfully applied. Contrary to semi-crystalline and amorphous polymers, thermotropic liquid crystalline polymers (LCPs) do not change into an isotropic liquid during melting. Instead, they possess anisotropic properties in their liquid phase. Within the scope of this work, this special group of polymers was investigated with regard to its suitability for processing by means of fused filament fabrication. Using an LCP with a low melting temperature of around 280 °C is compared to processing an LCP that exhibits a high melting temperature around 330 °C. In doing so, it was revealed that the achievable mechanical properties strongly depend on the process parameters such as the direction of deposition, printing temperature, printing speed and layer height. At a layer height of 0.10 mm, a Young's modulus of 27.3 GPa was achieved. Moreover, by employing an annealing step after the printing process, the tensile strength could be increased up to 406 MPa at a layer height of 0.15 mm. Regarding the general suitability for FFF as well as the achieved uniaxial mechanical properties, the LCP with a low melting temperature was advantageous compared to the LCP with a high melting temperature.

The dual transportation channel of ionic strain sensor constructed by amorphous polymer chains and two-dimensional nanoplatelets

A large amount of ions favors high ionic-conductivity, but remarkably reduces the sensitivity of hydrogel-based wearable sensors, which severely limits their advanced applications. Herein, this contradiction is successfully overcome by the strategy of constructing the dual-ion transportation channels (DITC) in hydrogels. Specifically, using an anti-freezing CaCl2, an amorphous polymer network is created in freeze-thawed polyvinyl alcohol (PVA) hydrogel, which induces the enlarged spacing between PVA chains and thus promotes the transportation of ions as the first channel. Secondly, the two-dimensional nanoplatelets-bentonite (BT) with electrostatic interaction with PVA chains construct a second layer of ion transportation channel, which is capable of reversibly transforming between the dense and loose distribution under external force and thus further improves the ionic sensitivity of hydrogel sensors. Contributed by this particular amorphous crosslinked network and DITC, the ultimate hydrogels represent excellent flexibility, stretchability, self-adhesion, freezing-tolerance, long-term stability, and the most important strain sensitivity even with high ion concentration, which can monitor both subtle and complicated movements (e.g., finger bending and hand writing). Therefore, the DITC strategy extends the design principle for highly sensitive ionic-hydrogel sensors and provides excellent potential for stretchable electronic sensors and intelligent detection of human motions.