Polymer最新文献

Energy conversion represents a challenge in various fields of applications such as soft robotics or microfluidics technologies, particularly in terms of electromechanical coupling for actuators. The dielectric elastomers are a variety of electroactive polymers (EAP) which require high electric fields to be used as actuators. It is well-known that the presence of ionic impurities can have an influence of their electro-mechanical response under high electric field (i.e. above 1 MV/m). More precisely, it can be responsible for the bending of the sample under constant electric field. Here, we investigate the impact of a small content, i.e. from 0.1 wt% to 10 wt% of an imidazolium Ionic Liquid (IL) on the electromechanical response of a soft epoxy-amine network. The interest of this study therefore lies in its position at the frontier between dielectric polymers and ionic polymers. Dielectric spectroscopy revealed a significant increase of electric conductivity (≈2 orders of magnitude) when adding only 0.1 wt% of IL and up to 4 orders of magnitude with 10 wt% of IL at T = 20 °C for f = 10 Hz. It also evidenced the presence of the electrode polarization for all the samples doped with IL. The bending test carried out at E = 0.1 MV/m revealed no bending for pure epoxy-amine and a slow kinetics of bending for all the samples doped with IL with displacement evolving throughout the experiment (i.e. over 4 h). As evidenced by dielectric spectroscopy and bending tests, it is clear that the presence of a small quantity of ionic moieties (whether doping agent or impurity) can strongly modify the electromechanical behavior of elastomer commonly described as dielectric.

Polyimide (PI), as a high-performance polymer widely used in aerospace, optoelectronics, microelectronics, etc., the properties it focused on in different areas of application were diverse. However, most of the past machine learning studies in polyimide property prediction were focused only on the prediction of a single property. This study focused on four major categories of properties of polyimide, including thermal (Tg, T_d5, T_d10, and CTE), mechanical (Ts and TM), dielectric (ε), and optical (λ_cutoff, T400, n_av, and Δn), totaling eleven properties. PI data synthesized from previous studies were collected. MorGan fingerprints, improved MorGan fingerprints, RDkit and Mordred descriptors were selected as feature representations. Four ML models such as DNN, RF, XGBoost and BT were also built. Collectively, 176 machine learning models were trained for 11 predictions of properties. The performance and generalization ability of the models were confirmed by experimental validation, external validation and leave-one-out cross-validation. SHAP analysis was used to explain the optimal model for each property prediction from a physicochemical point of view and structural aspects, and three PIs with different structures were designed accordingly. Finally, a high-throughput virtual screening of nearly 7.6 million polyimides was performed based on the trained model. SA_scores was used to evaluate the ease of synthesis of each PI, and finally high-performance PIs with potential and easy to synthesize were selected for each field. This study could be expected to provide a guideline and a design framework for the application of PIs in various fields in the future.

Converting CO₂ into precious chemicals is considered to be a fundamental and effective tool for controlling the abundant CO₂ emitted. One of the most compelling methods for CO₂ conversion is the synthesis of cyclic carbonates by cycloaddition of CO₂ with epoxides. However, the development of materials with specific functionalities for CO₂ capture and conversion is still considered to be a significant challenge. Herein, a novel imidazolium salts and pyridine skeleton bifunctionalized hypercrosslinked polymers were prepared by FeCl₃-catalyted Friedel-Crafts alkylation reaction. Various analytical techniques were used to investigate the properties of the catalysts. The bifunctionalized heterogeneous catalysts exhibited outstanding catalytic performances for CO₂ cycloaddition under mild conditions with an excellent yield of up to 99 %. Besides, the catalyst could bear various epoxides and no significant loss of activity after 6 cycles. The properties of metal-free, solvent-free, cocatalyst-free, easy-to-prepare, mild conditions, facility separation and recyclability make the bifunctionalized hypercrosslinked polymers useful for CO₂ cycloaddition.

This research investigates the optimization of an advanced CO₂ capture material, using state of the art electron beam radiation technique, specifically an amine-loaded onto fly ash-incorporated polyacrylamide-based stable aerogel. The optimization study aims to enhance the PEI loading and thermal stability of the aerogel to capture CO₂. The response surface methodology (RSM) using central composite design (CCD) was employed to assess and optimize the impact of electron beam radiation dose, MBA concentration, and fly ash as independent variables on the PEI loading capacity as the response function. A good agreement between the model prediction and experimental results. This aerogel is characterized by its morphology, surface area and pore analysis chemical changes, and thermal stability. The introduction of fly ash enhanced the PEI loading up to 4.5 g/g and thermal stability below 190 °C of the PEI impregnated P (AAm-co-AAc) aerogel. In addition, the improved hybrid aerogel impregnated with PEI exhibited a CO₂ adsorption capacity up to 4.83 mmol/g at 30 °C. Remarkably, this aerogel maintained 98.3 % of its original capacity without any substantial loss after undergoing five regeneration cycles. The proposed optimization contributes to the development of sustainable and efficient materials for mitigating atmospheric CO₂ levels, addressing critical environmental challenges.

The development of high-performance thermosetting resins derived from epoxidized vegetable oil (EVO) has received significant attention in terms of the development of low-carbon economies. In this work, the all-atomic cross-linked models of anhydride-cured EVO were constructed and five cross-linking pathways involving distinct cure reactions were considered in the modelling process. The evolution of the number of distinct cure reactions and reactive groups of the cross-linked network under each pathway were monitored. The effects of the type of cure reaction, cure reaction probability, epoxy functionality of monomer, molar ratio of anhydride to epoxy, and anhydride structure on mass density, gelation transition, bulk properties, thermal properties, and mechanical properties of EVO-based thermosets were investigated in detail. The results show that the network exhibited minor difference in cure reactions but apparent thermo-mechanical properties of the thermosets. Etherification of epoxy groups and dehydration condensation caused the unfavorable thermo-mechanical properties. The glass transition temperature (T_g) is most affected by the molar ratio of anhydride to epoxy; whereas the Young's modulus is sensitive to the epoxy functionality of monomer. It is expected that the current work provides deep insights into the network formation and performance development of anhydride-cured EVO thermosets.

Thermally expandable microspheres (TEMs) with different foaming temperatures were utilized to develop bimodal polypropylene (PP)/TEM composite foams through injection molding. The introduction of TEMs significantly enhanced the crystallization process of PP and optimized its viscoelastic behavior. As the TEM content increased, the foam density decreased. An optimal state where the cell structure remained intact was obtained at a 6.0 wt% TEM content and the composite foam exhibited the best comprehensive mechanical properties. Furthermore, with the introduction of a second type of high-temperature TEM as the co-blow agent, bimodal cells with size centralized at 12 μm and 57 μm were generated in the PP matrix. When the ratios of two TEMs were controlled at 3.0 wt% each, the PP/TEM 3 + 3 % foam with an equal amount of co-blowing agent achieved 7 %, 94 %, and 101 % improvement in tensile strength, toughness, and strain-at-break compared with the PP/TEM 6 % foam with sole DU300x TEM blowing agent, owing to the synergetic effects of stress dissipation and redirection within the bimodal cell structures and the transverse toughening of the rigid TEM microspheres. In addition, the composite foam exhibits a smooth surface appearance with a low surface roughness since the TEM shell could effectively prevent the burst of the microspheres during foaming. This work provides a simple and effective approach for manufacturing bimodal foams with high toughness and high-quality surfaces.

Enhanced molecular mobility near the free (polymer–air) surface is crucial for advancing organic electronic devices, yet understanding the substrate's impact on the surface glass transition temperature (T_g^surf) as film thickness decreases remains limited. This study explores how polymer films possessing attractive, neutral, and unfavorable polymer–substrate interactions affect T_g^surf. Results show that neutral interactions have no effect, while attractive or unfavorable interactions can increase or decrease T_g^surf by up to ∼37 °C. The onset thickness for this change is smaller for attractive interactions (up to 37 nm) than for unfavorable interactions (>100 nm), supporting the observed broadening of the surface glass transition with attractive interactions. We surmise that segment exchange between surface and subsurface regions introduces disparate dynamic components at the surface. Therefore, attractive interactions causing a sharper change in T_g^surf with film thickness lead to a broader surface glass transition.

Polymer materials have gained widespread usage in the marketplace due to their lightweight properties, versatility, and cost-effectiveness. However, their susceptibility to scratches has been a longstanding issue. To overcome this shortcoming, surface texturing is one of the most low-cost, efficient ways to improve scratch performance by utilizing the inherent moldability of polymers. Textures rely on both the improvement of contact properties in terms of reduction in surface friction and the perceived visibility of scratches by masking the scratch-induced deformations. The current testing of the effectiveness of a particular texture design on scratch resistance requires tedious and costly psychophysical and/or experimental verification. In this paper, we present a comprehensive framework for scratch visibility analysis in virtual reality, integrating a novel scheme and finite element methods simulation. Our approach considers material, topographical, and optical properties, replicating perceived scratch visibility within the virtual space. The FEM model was found to overpredict the scratch depth and underpredict the shoulder height. A parametric study based on the material constitutive and surface properties has been carried out to highlight the effect of different material and surface factors on scratch performance and visibility. This study opens the door for a complete virtual design-development-analysis cycle for scratch performance evaluation of polymers.

Malleability and reprocessability of cross-linked polymers can be achieved via exchange reactions of the boronic ester crosslinking. Herein, we report a facile strategy to fabricate and modulate vitrimers by introducing intermolecular boron-nitrogen coordinated boronic ester crosslinking. Using a one-pot reaction, a series of boronic ester vitrimers based on polybutyl acrylate (PBA) was synthesized. The nitrogen containing monomer dimethylaminoethyl methacrylate (DMAEMA) was successfully copolymerized in the backbone to generate intermolecular boron-nitrogen (B–N) coordination. The presence of B–N coordination increases intermolecular interactions, leading to a denser crosslinked network structure and an elevated glass transition temperature. With the formation of B–N coordination, PBA-xB-yN samples at the same crosslinking density exhibit higher elongation at break and tensile strength. These samples dissipate more energy at the same strain and show a more pronounced strain rate dependency, highlighting the sacrificial role of the B–N coordination bonds. Stress relaxation experiments reveal that the intermolecular B–N coordination promotes faster relaxation of PBA-xB-yN compared to PBA-xB due to accelerated exchange dynamics of boronic ester. Mechanical reinforcement after recycling is observed in PBA-1B–2N, indicating that structural optimization of chemical and physical crosslinking occurs during thermal reprocessing. This study will provide a new strategy to fabricate boronic ester based vitrimeric materials with mechanical reinforcement and toughness enhancement.

Shish-kebab crystal is a crucial crystalline morphology in polymers, and its formation and evolution are paramount for achieving high-performance materials. In this study, using UHMWPE as an example, we employed precise temperature control in the gel molding process to prepare low-entangled UHMWPE gel films containing reserved shish crystals, Distinguished from other molding systems, gel molding, due to the presence of small-molecule solvents, not only reduces the entanglement degree of the system but also provides a favorable environment for molecular chain disentanglement, and thus is considered as a low-entanglement system that is easily disentangled. We investigated the structural evolution of the films at different stretching temperatures by employing in-situ WAXD, SAXS, USAXS, along with ex-situ SEM and DSC methods. Furthermore, the impact of entanglement degree on the evolution of crystal structures was explored through the change of molecular weight. 2D-USAXS results reveal the longer stripe scattering signals than previous studies, indicating a more pronounced ordered arrangement of shish crystals. Simultaneously, we discovered that only when molecular chains with an appropriate degree of entanglement were induced to disentangle by stretching with the presence of small-molecule solvents can the high orientation of crystals be facilitated, thereby promoting the evolution of crystal structure. Reserved shish crystals can induce crystal orientation during stretching and facilitate structural evolution. Building upon earlier investigations, this study innovatively through the dual-factor (the molecular weight and stretching temperature) control of the suitable entanglement degree and disentanglement conditions, allowing for reasonable control of the growth and evolution of shish-kebab crystals in low-entangled systems.