Macromolecular Materials and Engineering最新文献

The tunability of the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAM) to lower or higher temperatures, as well as the ease of modulation of the LCST phase transition kinetics broadens the scope of application of PNIPAM-based materials in biomedical fields. This work reports a facile approach to formulate a smart, injectable cellulose nanofibril (CNF)/PNIPAM hybrid gel. Hofmeister salts are used to induce ion-mediated gelation of the nanofibrils and PNIPAM chains, resulting in an interpenetrating network (IPN) structure. From rheological measurements, the hybrid material displays excellent structural integrity at room temperature and tunable thermo-stiffening around body temperature. De-swelling kinetics can be modulated by varying the nature and concentration of the Hofmeister ion used. The successful realization of the IPN hybrid gel structure is dependent on the molecular weight of PNIPAM used. Moreover, the hybrid gels show good thermo-reversibility during thermal cycling, as well as excellent injectability and remarkable self-healing post-injection, owing to shear-thinning and thixotropic characters. Since rheology is a crucial technique in the analysis of soft matter and flow behavior is fundamental for the design and synthesis of application-specific viscoelastic materials, the work reported herein provides a rheological basis for careful design and synthesis of smart gels.

Front Cover: High power, sunlight-simulated UV light induces radical polymerizations of (meth)acrylate-based monomers. During this process, mono-radicals can be generated through the H-abstraction mechanism, while bi-radicals can arise from photodissociation or oxygen initiation mechanisms. The generated free radicals facilitate self-initiation and self-crosslinking, rendering this technology efficient for synthesizing polymer networks without the need for added initiators or crosslinkers. This is reported by Wenqing Yan and co-workers in article 2399456.

Electrospun nanofiber membranes (ENMs) have emerged as a cutting-edge solution for membrane distillation (MD), recognized for their highly porous and interconnected architecture. This distinctive structure enables them to offer minimal mass transfer resistance, making them exceptionally suited for high-efficiency membrane-based separation processes. However, the very porosity that defines their strength also renders them vulnerable to fouling, scaling, and wetting during operation, which in turn compromises their performance. Current research efforts are geared toward overcoming these obstacles by refining the surface design and characteristics of ENMs. This review delves into the latest advancements in surface-enhanced electrospun nanofiber membranes tailored for MD applications. It discusses the existing gaps in research and provides forward-looking insights into the future of ENMs, spotlighting the development of membranes with precisely tunable surface attributes for optimized performance.

Polyethylene terephthalate glycol (PETG) is a novel amorphous shape memory polymer with excellent printability for 4D printing. In this article, ethylene-vinyl acetate (EVA) is used as a biocompatible and non-toxic copolymer to improve plasticity and shape memory performance of PETG. PETG-EVA blends are prepared and 3D printed using a melt mixing method and an upgraded fused deposition modeling (FDM) with a pneumatic feeding system. The results of the thermal analysis show that the blends exhibit two tan-delta peaks, each related to their components, and morphology images confirm that they are biphasic and immiscible with good compatibility. The morphology of both EVA10 and EVA30 matrix droplets is observed, with the droplets being larger for EVA30. The use of a pneumatic feeding system, along with the ability to control the output melt flow, results in the best printing ability for EVA30, with minimal microholes between the grids and interlayer cracks. The tensile strength of PETG-EVA blends ranged from 25.38 to 20.14 MPa, with the highest tensile strength achieved for EVA30. The shape memory performance of all three blends is similar; with shape recovery exceeding 90% in 20 s. Blends with higher EVA content exhibited faster shape recovery within the first 10 s.

Flexible microwave absorber (MAR), vital in advanced applications such as wearable electronics and precision devices, are highly valued for their lightweight, exceptional electromagnetic waves (EWs), and ease of fabrication. However, optimizing the electromagnetic parameters of microwave absorption materials (MAMs) to enhance absorption ability and expand effective absorption broadband (EAB, reflection loss (RL) <−10 dB) is a considerable challenge. Herein, a permittivity-attenuation evaluation diagram (PAED) is constructed using parameter scanning based on the Materials Genome Initiative to determine the ideal electromagnetic parameters and thickness, optimize absorption efficiency, and obtain highly efficient absorbers. Guided by the PAED, a multilayer MAR consisting of a “matching-absorption-reflection layer” and a dielectric loss gradient aligned with the direction of EWs propagation is developed. This design significantly enhances the EWs penetration and ensures effective absorption, attributed to the well-matched impedance and attenuation characteristics. As anticipated, the microwave absorption of the absorber (density = 0.063 g cm⁻³) is optimized, with an RL of −34 dB at d = 4 mm and an EAB covering the entire X-band (8.2–12.4 GHz). This study presents a novel approach for establishing a material database for MAMs and developing high-performance absorbers characterized by thinness, lightness, broad operational frequency range, and robust absorption capacity.

Reversible adhesives are crucial for a circular economy of composites as they play a key role for rework, repair, and recycling of adhesively bonded components. Herein, electrically debondable adhesives are prepared by introducing ionic liquids in dynamic thiol–epoxy networks. The function of the ionic liquid in the networks is threefold as it accelerates the curing reaction between thiol and epoxy monomers, facilitates electrical debonding, and catalyzes thermoactivated transesterification reactions, required for rebonding at elevated temperature. A library of 1,3-dibutylimidazolium-based ionic liquids with varying anions is synthetized and it is found that 1,3-dibutyl-1H-imidazol-3-ium dicyanamide (DiButIm─N(CN)₂) is superior in accelerating bond-exchange reactions between hydroxy and ester moieties at elevated temperature. Thus, a thiol–epoxy resin containing 20 wt% of DiButIm─N(CN)₂ is used to impregnate glass fiber mats yielding adhesive connections for aluminum substrates with 10.2 MPa pull-off strength. The adhesive connections are successfully debonded at the metal–adhesive interface by applying 120 V. The samples are then rebonded via the thermoactivated change in the networks’ viscoelastic properties and ≈80% (8.1 MPa) of their original bond strength can be regained. By providing a simple strategy to synthetize reversible adhesives, this approach paves a way toward improved recyclability and repairability of adhesively bonded structures.

New nanocomposites based on biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) are processed via extrusion, using low content of calcined hydrotalcite (CHT) and cloisite 20A (C20A) as additives (3 wt%). The aim of this work is to characterize the thermal and viscoelastic response of the structures induced by the presence of the additives. Field-emission scanning electron microscopy and laser profilometry are utilized to analyze the effect of the additives on the surface finish of extrusion filaments, detecting a smoother surface induced by additives. A lower degradation temperature is observed via thermogravimetry for composite containing CHT (PHBV+3%CHT), while such a phenomenon is not present in composite with C20A (PHBV+3%C20A). An increase in crystallinity due to the nucleating effect of additives is measured via differential scanning calorimetry. The intercalation of the biopolymer in the layered structure of the additives is observed via X-ray diffraction, reflecting the effective interaction in the composite matrix. The viscoelastic behavior of the samples is evaluated by means of rheology and dynamic-mechanical analysis, showing a non-Newtonian behavior and an enhancement of the vitreous state response. All results converge to the conclusion that the incorporation of the additives induces the formation of long-term structures that present variable sensitivity to temperature and frequency.

When it comes to sustainable and efficient energy solutions, organic semiconductors can play an important role in thermoelectric applications, since they are non-toxic, cheap, made of abundant chemical species, and show intrinsically low thermal conductivities. Their electrical conductivity can be optimized via doping. Yet, thermal conduction should be as low as possible and, to this end, the atomic scale mechanisms behind heat transport –e.g. the correlation between morphology and thermal conductivity or the role of doping– should be understood in detail. Fully atomistic molecular dynamics calculations of the lattice thermal conductivity of doped poly(3,4-ethylenedioxythiophene) (PEDOT) highly ordered, quasi-crystalline nanofibers are presented here. It is found that the conductivity along the backbone direction is not necessarily the highest, but it depends on the length of the PEDOT chains, thus the degree of anisotropy depends on the the aspect ratio of the nanofiber. Indeed, transport along the lamellar direction can be of the same order or higher than that of the backbone if their lengths are comparable. These results challenge the usual expectation that thermal conduction along the backbone largely exceeds those along the lamellar and π − π direction and have the important consequence that the anisotropy could be leveraged in thermal management applications.

The predominant use of synthetic materials, such as fiberglass and polymeric foams, for thermal and acoustic insulation in the construction sector contributes to the recalcitrant waste accumulation in the environment and is not economically sustainable in the long term. This is because they are developed with linear economy standards, they are neither reusable nor recyclable, and, at their end of lifecycle, they are not compostable, with a great amount of them finishing in landfills. This work is focused on the development of natural, self-growing mycelium-biocomposites as sustainable alternatives to these conventional synthetic materials. Specifically, fungal mycelium derived from the nonpathogenic fungal strain Pleurotus ostreatus is fed by coffee silverskin flakes, a lignocellulosic agrowaste from roasted coffee seeds, forming 3D biocomposites. The physicochemical properties of the obtained composite are thoroughly investigated, with a final focus on their thermal and acoustic insulation properties. As proved, the natural agrowaste-mycelium composites possess high porosity and thus low density, good thermal properties, and satisfactory sound absorption capability. Such properties combined with the minimal energetic requirements for their growth and their fully compostable end-of-life nature make them valuable alternatives for thermal and acoustic insulation in building construction, among other applications, promoting environmental and economic sustainability.