Porous Polymeric Materials Research Articles

Fast Synthesis of Olefin-Linked Covalent Organic Frameworks via Supercritically Solvothermal Polymerization.

Covalent organic frameworks (COFs) are newly emerging yet rapidly developed porous crystalline polymeric materials, which feature topological designability, structural diversity, and porosity tunability. However, most of the reported COFs hitherto are prepared by a solvothermal method, which needs a long reaction time, especially for the olefin-linked COFs, which hinders their practical applications. Herein, we report the fast growth of olefin-linked COFs synthesized by the supercritical solvothermal method under supercritical carbon dioxide conditions. Via optimization of the reaction conditions, olefin-linked COFs are prepared within 6 h, which is period much shorter than that of the traditional solvothermal method. The as-obtained COFs feature two distinct morphologies, namely, spherical and rod-like. Interestingly, the rod-like crystal shows polarized light extinction and rebrightening phenomena, indicating the high crystallinity. After being doped with I2, the obtained I2@COFTMT-PA shows a Hall mobility of 1.94 cm2 V-1 S-1, indicating its potential applications in optoelectronics. This work expands the application of the supercritically solvothermal method to the fast growth of olefin-linked COFs and solves a long-standing challenge in chemical science, which opens up opportunities for basic research as well as practical applications of olefin-linked COFs and other polymeric materials.

Porous polymeric materials prepared via pickering emulsion templating targeted as a bronsted acid catalyst in room-temperature biodiesel production

The present work is about preparing a set of magnetic macroporous polymers using the Pickering high internal phase w/o emulsions (HIPEs) templating method. The octyl-modified core-shell magnetic nanoparticles (Fe3O4@SiO2-Octyl) were used as a solid stabilizer and Span 80 surfactant to stabilize the HIPEs. The effect of Fe3O4@SiO2-Octyl content, Span 80 content, and molar ratio of styrene/divinylbenzene (St/DVB) on physical properties, morphology, pore size, and void size of the macroporous polyHIPEs was precisely evaluated. The optimized polyHIPE prepared by 2 wt% of Fe3O4@SiO2-Octyl nanoparticles, 9 wt% of Span 80, and St/DVB molar ratio of 8 with the porosity of 86±1.1 % and an average pore size of 4.1 µm was selected as catalyst support to functionalize with sulfonic acid groups. The resulting catalyst (polyHIPE–SO3H) showed excellent performance in reacting long-chain free fatty acids (FFA) with methanol to give fatty acid monoalkyl esters (FAMEs) at room temperature. In this way, the polyHIPE–SO3H was found to be very active and reusable in the mentioned process, giving high yields (∼92–98 %) of various biodiesel compounds under very mild reaction conditions and recycling in the next subsequent runs without significant loss of activity.

3D Covalent Organic Framework Membranes for Molecular Separations.

Membrane separation has become an indispensable separation technology in social production, playing an important role in drug production, water purification, etc. The key core of membranes lies in achieving efficient and precise sieving between substances. As a result, a typical trade-off arises: highly permeable membranes usually sacrifice selectivity and vice versa. To address this dilemma, long-term research has focused on comprehensive understanding and modelling of synthetic membranes at various scales. A significant advancement in this arena is the advent of three-dimensional covalent organic framework (3D COF) membranes, a novel category of long-range ordered porous organic polymer materials. Characterized by an abundance of interconnected channels, diverse pore wall properties, tunable structures, and robust thermal and chemical resilience, 3D COF membranes offer a promising approach for efficient substance separation. This review undertakes a meticulous investigation of the synthesis and physicochemical properties of 3D COF membranes, accentuating the underlying design principles, fabrication methods, and application attempts. A comprehensive assessment of their research trajectory and current standing in the field of membrane processes is provided. The review culminates in a forward-looking outlook, summarizing future research directions and highlighting the substantial potential of this innovative work to shape the future of efficient membrane separation processes.

Complex pattern formation governed by a Cahn–Hilliard–Swift–Hohenberg system: Analysis and numerical simulations

This paper investigates a Cahn–Hilliard–Swift–Hohenberg system, focusing on a three-species chemical mixture subject to physical constraints on volume fractions. The resulting system leads to complex patterns involving a separation into phases as typical of the Cahn–Hilliard equation and small scale stripes and dots as seen in the Swift–Hohenberg equation. We introduce singular potentials of logarithmic type to enhance the model’s accuracy in adhering to essential physical constraints. The paper establishes the existence and uniqueness of weak solutions within this extended framework. The insights gained contribute to a deeper understanding of phase separation in complex systems, with potential applications in materials science and related fields. We introduce a stable finite element approximation based on an obstacle formulation. Subsequent numerical simulations demonstrate that the model allows for complex structures as seen in pigment patterns of animals and in porous polymeric materials.

Design and assembly of conductive covalent organic frameworks for proton exchange membrane application

To develop proton exchange membranes (PEMs) with robust structure stability and remarkable proton conductivity and explore their application in PEMs fuel cells have significant implications for realizing reduced carbon emission and environmental pollution. Covalent organic frameworks (COFs), as crystalline porous polymer material composed of organic monomers and connected by covalent bond, possess specific framework, inherent porosity, adjustable functional group and eminent thermal/chemical structure stability. Therefore, COFs display prominent superiorities in constructing rigid ordered proton transfer channels and improving fuel cell performance long‐term durability. In this review, the proton conduction properties of extrinsic proton‐conductive COFs (incorporating carriers into the pore), intrinsic proton‐conductive COFs (introducing conductive groups on the backbone) and combined extrinsic/intrinsic proton‐conductive COFs in the form of pressed pellets are discussed in detail. Meanwhile, proton‐conductive COFs related PEMs, including COFs‐related polymer‐based composite membranes, COFs‐based composite membranes and self‐supporting COFs membranes are also systematically summarized. In addition, the existing challenges are analyzed and future outlooks are addressed.

Tuning (Photo)Electronic Properties of an Electron Deficient Porous Polymer via n-Doping with Tetrathiafulvalene.

Charge-transfer complex formation within the pores of porous polymers is an efficient way to tune their electronical properties. Introduction of electron accepting guests to the electron donating hosts to conduct their p-doping is intensively studied in this context. However, the vice versa scenario, n-doping by treating the electron deficient (i.e., n-type) porous polymers with electron donating dopants, is rare. In this work, synthesis of an n-type phenazine based conjugated microporous polymer and its exposure to strong electron donating tetrathiafulvalene (TTF) dopants are presented. The fundamental physical characterizations (e.g., elemental analysis, gas sorption) showed that the vacuum impregnation technique is a good approach to load the guest molecules inside the pores. Moreover, the formation of charge-transfer complexes between the phenazine building blocks of the polymeric network and TTF dopants are confirmed via spectral techniques such Fourier transform infra-red, UV-vis, steady-state/time-resolved photoluminescence, and transient absorbance spectroscopies. Effect of the doping to the electronical properties is monitored by employing photoelectrochemical measurements, which showed lower charge-transfer resistivity and nearly doubled photocurrents after the doping. The study is, therefore, an important advancement for the applicability of (n-type) porous polymeric materials in the field of photo(electro)catalysis and organic electronics.

Porous BINAP-based polyaromatic polymers for the continuous base-free Ru-catalysed decomposition of aqueous formic acid

In this work, a Suzuki cross-coupling procedure towards highly porous BINAP-based polymeric Ru-catalyst materials with tunable specific surface areas (SSAs) were synthesized and their stability towards reducing conditions was investigated. After the removal of Pd impurities by an oxidative treatment with H2O2/HCl, P=O reduction and metal loading, the resulting catalysts were employed for the base-free ruthenium-catalyzed decomposition of aqueous formic acid to CO2 and H2 with TOFs of up to 134000 h−1 and TONs up to 920000.

Gamma‐ray‐induced modification of poly(ethylene terephthalate) and polypropylene solid materials with halogen‐containing olefins for X‐ray CT image contrast enhancement

AbstractIt is known that X‐ray CT of organic polymer materials usually provides low‐contrast images because of the low X‐ray absorption of these materials. In this paper, we describe a new method to enhance the contrast of X‐ray CT images of organic polymer materials. We demonstrate that gamma‐ray irradiation of poly (ethylene terephthalate) (PET) fibers in dichloromethane containing 2‐bromoethyl methacrylate, 2‐chloroethyl methacrylate, or 4‐bromostyrene results in the grafting of halogen‐containing oligomeric chains onto the PET fibers. Focused ion beam scanning electron microscopy (FIB‐SEM) and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) analyses revealed a homogeneous distribution of bromine atoms within the 2‐bromoethyl methacrylate‐modified PET fibers, not only on the surface. This uniform incorporation translated to a significant improvement in X‐ray CT image contrast compared with pristine fibers. Similar treatment of polypropylene pellets also enhanced the contrast of their X‐ray CT images. This is a new simple and effective method to enhance the X‐ray CT image contrast and potentially applicable to various polymer materials including polymer composites and porous polymer materials, readily allowing the observation of their 3D microstructures finely.

Monolithic conjugated microporous polymers with antibacterial activity for air filtration

The air pollution caused by particulate matters (PMs) poses a severe threat to the human health. In particular, the fine particles with diameter smaller than 2.5 μm (PM2.5) can be carriers of various bacteria and viruses, accelerating spread of epidemic. In this work, we synthesized two robust and flexible conjugated microporous polymer (CMP) aerogels for PMs removal, via one-step coupling polymerization of arylethynylenes and aryl halides with different molecular configuration. The resulting CMP aerogels comprise of hollow nanotubes with 3D porous network and high surface areas up to 660 m2/g. The efficiency of CMP aerogels for PM2.5 and PM10 was 99.5 ± 0.3 % and 99.8 ± 0.1 % with a long-term durability. In combination with their physicochemical stability and inherent surface hydrophobicity, a high efficiency for PM2.5 filtration more than 99.6 ± 0.1 % also can be obtained at a high humidity at room temperature both for the two CMP aerogels. In addition, benefiting from the rich alkynyl groups in skeletons, post-modification of the resulting CMP aerogels with thiol-yne chemistry followed by silver ion uptake gives rise to antibacterial materials with outstanding activity for gram-positive strains far superior to other porous organic polymer materials. This work provides a new avenue to fabricate bifunctional CMPs derived porous aerogels for air filtration with high performance and antibacterial activity, and is expected to expand the application of CMPs in environmental purification.

Fluorine Incorporation for Enhanced Gas Separation Performance in Porous Organic Polymers: Investigating Reaction Pathways and Pore Structure Control.

The precise control of pore structures in porous organic polymer (POP) materials is of paramount importance in addressing a wide range of challenges associated with gas separation processes. In this study, we present a novel approach to optimize the gas separation performance of POPs through the introduction of fluorine groups and figure out an important factor of reaction decision that whether the AlCl3-catalyzed polymerization is Scholl reaction or Friedel-Crafts alkylation. In the chloroform system, the steric hindrance of function groups could make direct coupling between the benzene rings difficult, which would lead to part solvent knitting (Friedel-Crafts alkylation) instead. The fluorinated polymers show enhanced surface area and pore size characteristics. Notably, the fluorinated polymers exhibited significantly improved adsorption and separation performance for SF6, as evidenced by an ideal adsorbed solution theory selectivity (SF6/N2, v: v = 50:50, 273 K) increase of 75.0, 668.8, and 502.8% compared to the nonfluorinated POPs. These findings highlight the potential of fluorination as a strategy for tailoring the properties of POP materials for advanced gas separation applications.

Integrated Framework to Model Microstructure Evolution and Decipher the Microstructure-Property Relationship in Polymeric Porous Materials.

Unraveling the microstructure-property relationship is crucial for improving material performance and advancing the design of next-generation structural and functional materials. However, this is inherently challenging because it requires both the comprehensive quantification of microstructural features and the accurate assessment of corresponding properties. To meet these requirements, we developed an efficient and comprehensive integrated modeling framework, using polymeric porous materials as a representative model system. Our framework generates microstructures using a physics-based phase-field model, characterizes them using various average and localized microstructural features, and evaluates microstructure-aware properties, such as effective diffusivity, using an efficient Fourier-based perturbation numerical scheme. Additionally, the framework incorporates machine learning methods to decipher the intricate microstructure-property relationships. Our findings indicate that the connectivity of phase channels is the most critical microstructural descriptor for determining effective diffusivity, followed by the domain shape represented by curvature distribution, while the domain size has a minor impact. This comprehensive approach offers a novel framework for assessing microstructure-property relationships in polymer-based porous materials, paving the way for the development of advanced materials for diverse applications.

Flexible porous coordination polymer with multiple configurations for guest recognition and switchable CO2 sorption properties

Abstract Realizing multiple metastable configurations in a single porous coordination polymer has long been pursued to achieve switchable functionality. In this study, we reported multiple configurations in one porous coordination polymer material via the design of the adjustable intraframework π–π stacking moieties. We demonstrated that the porous coordination polymer can accommodate three different open pore phases depending on the type of solvent. Furthermore, this porous coordination polymer exhibits three distinct closed pore phases depending on the activation approaches, demonstrating different CO2 sorption properties.

Degradable biporous polymeric networks based on 2-methylene-1,3-dioxepane: Towards hierarchically structured materials meant for biomedical applications

For the first time, the preparation of doubly porous “poly(ε-caprolactone)-like” networks through free-radical ring-opening copolymerization of 2-methylene-1,3-dioxepane with divinyl adipate was achieved via a double porogen templating approach. This versatile strategy allowed for the formation of macropores of around 150 μm generated by removal of sieved and sintered NaCl particles in water, while smaller pores in the 1–10 μm range were created by phase separation during the copolymerization process through a syneresis mechanism in the presence of a porogenic solvent. The chemical nature of the as-obtained scaffolds was evidenced by Raman spectroscopy. The two distinct porosity levels could be examined by scanning electron microscopy and mercury intrusion porosimetry. The nature of the porogenic solvent as well as its volume proportion and the amount of crosslinking agent in the polymerization feed allowed for finely tuning the porous features of the micropores. The crucial role of the double porosity of such biporous scaffolds on their water uptake and mechanical properties under compression was assessed by comparing them with their monoporous analogues, while their degradability was investigated in different alkaline aqueous media. The double porosity enabled a synergistic effect regarding the water uptake of the resulting scaffolds when compared to their monoporous counterparts. Doubly porous polymeric materials with appropriate mechanical properties were obtained, possessing high compressibility and shape memory behavior upon consecutive compression cycles. Finally, these materials display degradation rates that could be controlled depending on medium pH.

Dynamic fabrication of porous polymeric coating for efficient passive daytime radiative cooling using in-situ pore-formation strategy

Porous polymeric material has emerged as promising choice for making passive daytime radiative cooling (PDRC) emitter. However, it is still an unmet challenge to establish a flexible method to achieve dynamic pore-formation for the purpose of studying the relationships between the porous structure and the resultant cooling performance. The current study reports a novel strategy to construct asymmetric multi-layered porous structure in situ within the matrix of pre-formed polystyrene coating. The modified procedure of inverse emulsion - breath figure method is adopted, and solvent-nonsolvent exchanging process is also involved during the pore-formation process, leading to the formation of hierarchical porous structure with rather high porosity. Geometrical features of the generated pores are effectively regulated by simple adjustment of the experimental parameters of the water ratio of the emulsion and the humidity. The relationship between the pore structure and optical & cooling properties has been established based on experimental facts. By tuning of optimal conditions, the in-situ pore-formation can endow the polymeric coating with high solar reflectance (∼85 %) and infrared emittance (∼98.4 %), resulting in passive temperature drop of 12 °C and cooling power of 91 W/m2. This study provides experimental information to get some insight into the designing principle of porous polymeric PDRC materials, and formulates unique strategy of in-situ functionalization via structural transformation upon polymeric objects or devices.

Tailoring the covalent organic frameworks based polymer materials for solar-driven atmospheric water harvesting

Atmospheric water harvesting through reticular materials is an innovation that has the potential to change the world. Here, this study offers a technique for creating a solar-powered hygroscopic polymer material for atmospheric water harvesting with the reticular materials. The results show that the porous hygroscopic polymer materials can achieve high performance with high vapor capture (up to ac. 28.8–49.7 mg/g at 28–38 %RH and 25 ℃), rapid photothermal conversion efficiency (up to 32.2 ℃ within 15 min under 1000 W/m−2 light at 25 ℃), a low desorption temperature (lower than 40 ℃), and an effective water release rate. Besides, the material also has excellent water-retention properties, which can effectively store desorbed liquid water in polymer networks for use by vegetation during water demand periods. The strategy opens new avenues for atmospheric water-harvesting materials, which will hopefully solve the global crisis of freshwater shortages.

Contribution of the radiative transfer mechanism to the total thermal conductivity of anisotropic porous materials

In order to understand the performance of polymeric porous materials as heat insulators, the contribution of the radiative transfer mechanism in porous materials with high ratios of anisotropy is studied. Porous materials based on extruded polystyrene (XPS) with relative density in the range of 0.03−0.05 and with a range of anisotropy ratios of 0.6−1.4 have been selected for this research. The study begins with a characterization of the selected materials in terms of porous structure and thermal conductivity as a function of temperature. Then, the radiative contribution for each of the three main directions of the materials is obtained by three independent methodologies: Fourier Transform Infrared (FTIR) spectroscopy, derivation from the total conductivity using theoretical models, and theoretical calculation from the model proposed by Glicksman. The results show similar trends for all methods and confirm clear differences between each direction, showing a significant reduction of the radiative contribution and, thus, the total conductivity, if the material is oriented geometrically towards the direction in which the pore size is the smallest. Indeed, reductions of 17−20% in the total conductivity can be achieved at temperatures ranging from 10−40°C if the material is reoriented as stated.

CTAB modified metakaolin-based geopolymer microspheres for the selective adsorption and recovery of TcO4−/ReO4−

With the increase of radioactive wastewater, it is a major challenge to efficient removal of TcO4− from radioactive wastewater. So far, cationic metal organic frameworks (MOFs), cationic covalent organic frameworks (COFs), cationic polymeric networks (CPNs) and porous organic polymer materials (POPs) can remove TcO4− efficiently, but the cumbersome preparation process and high cost limit their practical applications. Herein, an efficient and low-cost CTAB-modified metakaolin-based geopolymer microspheres (CTAB@MGMs) with excellent adsorption properties for ReO4− is simply and rapidly synthesized by dispersion-pelletizing-solidification and vacuum infusion methods. CTAB@MGMs has fast adsorption kinetics (equilibrium in 10 min), a wide pH application range (2–10) and high selectivity in competing ions (PO43−, SO42−, NO3−, Cl−) and real waters (tap water, surface water, seawater). Importantly, complete desorption of the adsorbed sample can be realized by ethanol and MGMs can be recycled without performance decay. Meanwhile, ethanol recycling was achieved by spin-evaporation of desorption solution and a novel compound CTA-ReO4 was generated. We have analyzed and reported the crystal structure of CTA-ReO4 (CCDC Numbers: 2282273) for the first time and revealed the mechanism that ReO4− is removed by electrostatic and coordination synergism with quaternary ammonium salts after ion exchange. CTAB@MGMs is a low-cost, novel and reusable adsorbent with potential use for the removal of TcO4− from radioactive wastewater.

Analyzing the effects of polymeric dielectric materials on micro capacitive pressure sensors: A model incorporating displacement-dependent porosity

Recently, the extensive utilization of porous polymeric materials to amplify the sensitivity of capacitive devices is noticeable. The absence of an effective mathematical model for studying these devices has spurred the development of a comprehensive mathematical model in the current work. This model is formulated to analyze the static and dynamic behavior of systems incorporating a porous polymer dielectric material within the gap between flexible and fixed microplates. The derived nonlinear governing equations encompass the effects of electrostatic force, von-Karman nonlinear strains, and displacement-dependent porosity. Employing spatial decomposition, the resulting nonlinear algebraic equations and ordinary differential equations are leveraged to study the static and transient dynamic behavior, as well as the frequency response of the sensor using a learning approach. Two scenarios are investigated to assess the impact of various geometrical and physical parameters on sensor sensitivity one with a polymeric material and another without, each with distinct parameter values. The results reveal that the inclusion of a polymeric dielectric material increases electrostatic force but concurrently elevates the equivalent stiffness of the structure. The effectiveness of using a polymeric dielectric material is contingent upon the specific geometrical and physical properties of the sensor. Moreover, the obtained results in simplified cases are compared to existing numerical and experimental data, demonstrating a high degree of agreement. This work significantly contributes to advancing the understanding of sensors incorporating porous polymer dielectric materials and underscores their potential for enhanced sensitivity across diverse applications.

Sub-ambient radiative cooling with thermally insulating polyethylene terephthalate aerogels recycled from plastic waste

We demonstrate that the aerogels produced from the polyethylene terephthalate (PET) fibers, recycled from plastic bottle wastes, can function both as a radiative cooler and a thermal insulator. An object under and in contact with the recycled PET aerogel is thermally insulated from the surroundings and, at the same time, cooled below ambient temperature via radiative cooling. These dual capabilities are tested under the warm sky of Singapore with more than 420 W/m2 downwelling. With a 0.48 cm thick recycled PET aerogel, a heat transfer coefficient of 1.67 W/m2·K is measured when the object underneath is cooled by 2 °C from ambient temperature. Even under a 4.5 cm thick recycled PET aerogel, completely opaque to the thermal emission and having a heat transfer coefficient less than 1 W/m2·K, a sub-ambient radiative cooling is observed. Our measured heat transfer coefficient is lower than that of other porous polymer materials or aerogels reported to date as a radiative cooling substrate. Our results demonstrate that the recycled PET aerogels are a multi-functional material, integrating radiative cooling and thermal insulation in a single substrate. Produced by processing waste materials, the recycled PET aerogels hold promise to be a highly scalable and sustainable thermal management solution, with a positive impact on the environment.

Phase-separated porous nanocomposite with ultralow percolation threshold for wireless bioelectronics.

Realizing the full potential of stretchable bioelectronics in wearables, biomedical implants and soft robotics necessitates conductive elastic composites that are intrinsically soft, highly conductive and strain resilient. However, existing composites usually compromise electrical durability and performance due to disrupted conductive paths under strain and rely heavily on a high content of conductive filler. Here we present an in situ phase-separation method that facilitates microscale silver nanowire assembly and creates self-organized percolation networks on pore surfaces. The resultant nanocomposites are highly conductive, strain insensitive and fatigue tolerant, while minimizing filler usage. Their resilience is rooted in multiscale porous polymer matrices that dissipate stress and rigid conductive fillers adapting to strain-induced geometry changes. Notably, the presence of porous microstructures reduces the percolation threshold (Vc = 0.00062) by 48-fold and suppresses electrical degradation even under strains exceeding 600%. Theoretical calculations yield results that are quantitatively consistent with experimental findings. By pairing these nanocomposites with near-field communication technologies, we have demonstrated stretchable wireless power and data transmission solutions that are ideal for both skin-interfaced and implanted bioelectronics. The systems enable battery-free wireless powering and sensing of a range of sweat biomarkers-with less than 10% performance variation even at 50% strain. Ultimately, our strategy offers expansive material options for diverse applications.