Search

Polyvinyl alcohol is the most commercially water-soluble biodegradable polymer, and it is in use for a wide range of applications. It shows good compatibility with most inorganic/organic fillers, and enhanced composites may be prepared without the need to introduce coupling agents and interfacial modifiers. The patented high amorphous polyvinyl alcohol (HAVOH), commercialized with the trade name G-Polymer, can be easily dispersed in water and melt processed. HAVOH is particularly suitable for extrusion and can be used as a matrix to disperse nanocomposites with different properties. In this work, the optimization of the synthesis and characterization of HAVOH/reduced graphene oxide (rGO) nanocomposite obtained by the solution blending process of HAVOH and Graphene Oxide (GO) water solutions and ‘in situ’ reduction of GO is studied. The produced nanocomposite presents a low percolation threshold (~1.7 wt%) and high electrical conductivity (up to 11 S/m) due to the uniform dispersion in the polymer matrix as a result of the solution blending process and the good reduction level of GO. In consideration of HAVOH processability, the conductivity obtained by using rGO as filler, and the low percolation threshold, the nanocomposite presented here is a good candidate for the 3D printing of a conductive structure.

Lightweight porous materials have attracted burgeoning interest in recent research on highly effective electromagnetic interference (EMI) shielding materials owing to their tunable density and low thermal conductivity. In this paper, acrylic copolymer (AC)/silver nanowire (AgNW) foams with segregated networks were synthesized by high-speed mechanical mixing followed by a hot-pressing method. As the AgNW volume content was increased from 0.12 vol% to 0.31 vol%, the electrical conductivity of the foams was increased from 0.89 S m−1 to 142.99 S m−1, which is attributed to the presence of a gradually perfect segregated AgNW network. A porous structure surrounded by AgNWs, as well as excellent electrical conductivity, endows the resultant foams with an outstanding EMI shielding effectiveness (SE) that reaches as high as 63 dB and an excellent specific SE (defined by the SE to density ratio) of 180 dB cm3 g−1 in the X-band (8.2 GHz ~ 12.4 GHz). Moreover, the obtained AC/AgNW foams exhibit low and tuneable thermal conductivity, which can be varied from 0.022 W m−1 K−1 to 0.147 W m−1 K−1 by controlling the foam density (0.07 g cm−3–0.35 g cm−3). Lightweight AC/AgNW foams with high EMI SE and low thermal conductivity can be potentially applied in the field of aerospace and wearable smart material.

A new procedure for ultrasonication-induced atom transfer radical polymerization (sono-ATRP) in aqueous media was developed. Polymerizations of oligo(ethylene oxide) methyl ether methacrylate (OEOMA) and 2-hydroxyethyl acrylate (HEA) in water were successfully carried out in the presence of ppm amounts of CuBr2 catalyst and tris(2-pyridylmethyl)amine ligand when exposed to ultrasonication (40 kHz, 110 W) at room temperature. Aqueous sono-ATRP enabled polymerization of water-soluble monomers with excellent control over the molecular weight, dispersity, and high retention of chain-end functionality. Temporal control over the polymer chain growth was demonstrated by switching the ultrasound on/off due to the regeneration of activators by hydroxyl radicals formed by ultrasonication. The synthesis of a well-defined block copolymer and DNA–polymer biohybrid was also successful using this process.

Hybrid MXene/reduced graphene oxide aerogel microspheres (MXene/rGOAMs),where MXenes are two-dimensional (2D) transition metal carbides, with abundant macro/meso/micro multi-scale pores and self-supporting structure, are prepared by electrospraying followed by freeze-drying and then thermal annealing. A center-diverging structure with well-aligned microchannels is formed within each microsphere, which can be maintained after thermal reduction. Such highly ordered 3D hybrid mesoporous network has been tested for the hydrogen evolution reaction (HER) because it may prevent the stacking of the 2D layers, thus enhancing the mass transfer. Actually, in the case of Ti3C2Tx/rGOAMs, obtained with an optimized MXene:GO mass ratio and after a thermal treatment at 400 °C, a better HER performance with respect to the bulk Ti3C2Tx aerogel or the MXene/GO composite is observed (η10=-336 mV), suggesting an accelerated mass transfer through different inter-sheets when the 3D mesoporous microsphere networks are created. The Ti3C2Tx/rGOAMs also exhibit enhanced HER activity compared to rGOAMs, suggesting that the MXene plays a key role due to the presence of titanium atoms with a low valence state.

It is of great significance for electromagnetic interference (EMI) shielding materials to fulfill long-lasting service requirements. Here, waterborne polyurethane (WPU) was coated on the surface of a silver nanowire (AgNW) network with sputter-deposited nickel nanoparticles (NiNPs) by dip-coating technology to improve their durability. After five dip-coating cycles, a WPU layer nearly coated the whole surface of the hybrid papers, and only a fraction of the metal filler is bare. The resultant hybrid papers exhibit an electrical conductivity of ∼3500 S m−1, remnant magnetization of 0.03 emu g−1, saturation magnetization of 0.10 emu g−1, and coercivity of 256 Oe. On the one hand, the presence of the WPU coating does not affect the shielding effectiveness (SE) of the hybrid papers; on the other hand, the WPU coating enhances the ability to resist tape peeling. Moreover, the resultant hybrid papers still maintain the original SE value (∼80 dB), even after exposure to air for 5 months owing to the isolation effect of the WPU coating, implying long-lasting durability. The results confirm that the obtained hybrid papers can meet the requirements of practical applications.

As an extraordinarily lightweight and porous functional nanomaterial family, aerogels have attracted considerable interest in academia and industry in recent decades. Despite the application scopes, the modest mechanical durability of aerogels makes their processing and operation challenging, in particular, for situations demanding intricate physical structures. "Bottom-up" additive manufacturing technology has the potential to address this drawback. Indeed, since the first report of 3D printed aerogels in 2015, a new interdisciplinary research area combining aerogel and printing technology has emerged to push the boundaries of structure and performance, further broadening their application scope. This review summarizes the state-of-the-art of printed aerogels and presents a comprehensive view of their developments in the past 5 years, and highlights the key near- and mid-term challenges.

A formidable scientific challenge for the development of self-healing polymers is how to rationally design molecular architectures that could integrate both highly efficient healing functions and excellent mechanical performances. Here, we present a novel rigid and tough but more healable polymer network enabled by self-catalytic cooperative multiple dynamic moieties (CMDMs) containing metal–ligand coordinations, multiple hydrogen bonds and reversible urea bonds. The strength and toughness of the materials are improved significantly via strong supramolecular interactions of CMDMs, resulting in a modulus, tensile strength and toughness up to 797.4 MPa, 73.6 MPa and 218.2 MJ m−3, respectively. The metal–ligand coordinations of CMDMs facilitate the dynamic exchange reactions between the urea bonds of CMDMs through a self-catalytic mechanism, providing the material with a much higher healing efficiency of 90% compared with 48% for the control sample without metal–ligand coordinations. CMDMs provide a novel paradigm for designing robust healable materials by integrating dynamic covalent bonds and supramolecular interactions into one single moiety.

Self-healing and recycling of fiber reinforced polymer (FRP) composites are of great significance towards pursuing a sustainable and circular economy, but remain a huge challenge due to the infusible and insoluble properties of thermoset polymers. The newly developed dynamic covalent polymers provide a great opportunity to resolve this issue for FRPs. Here we developed a novel type of dynamic covalently cross-linked polyacylsemicarbazide exhibiting a high modulus and self-healing/recycling capability due to the reversible properties of the dynamic acylsemicarbazide (ASC) moieties. Introducing different ASC moieties composed of different dihydrazides into the polymer can dramatically tune the mechanical, self-healing and reprocessing properties. An optimized polyacylsemicarbazide with a Young's modulus of ∼2.84 GPa, a stress at break of ∼100 MPa and a glass transition temperature of ∼123 °C exhibits a self-healing efficiency of ∼94.4% and great reprocessing properties. Furthermore, using this newly developed PASC material as the matrix resin, the carbon fiber reinforced polymer composite was successfully prepared through solution impregnation and thermal pressing. The composite exhibits an interlaminar shear strength of 40 MPa and a healing efficiency of 76.2%. The great dynamic reversible properties of ASC moieties enables the recycling of the carbon fiber and matrix resin, respectively, from the composites by a solvolysis method.

Achieving macro-damage repair of self-healing polymer materials is highly interesting and rarely reported. Realizing the dynamic characteristics of conventional chemical bonds will generate high-density dynamic covalent bonds in polymer materials, which should be favorable for the macro-damage repairing process as their dissociation can lead to more extensive depolymerization and also more complete disruption of the network. Herein, we accidently found that classical covalent urea bonds formed by primary amine and isocyanate possessed excellent dynamic characteristics in the absence of a catalyst. Density functional theory calculation suggests that the decomposition of a small molecule urea model does not easily occur due to the high energy barrier, while the experimental FTIR study of linear polyurea confirms the occurrence of urea bond decomposition at above 110 °C due to the entropy gain of the flexible polymer chains during heating. We demonstrated a kind of dynamic crosslinked polyurea–polydimethylsiloxane elastomer, in which polydopamine nanoparticles were introduced to produce rapid photo-thermal transition properties. The obtained composite elastomers exhibit a rapid solid–liquid transition under NIR exposure due to high-density dynamic urea bonds present in the polymer network and their fast dissociation rate, and thus possess excellent macro-damage repairing and shear-free reprocessing properties.

The realization of covalent adaptable networks with excellent mechanical and dynamic properties remains a major challenge. Herein, the acylsemicarbazide (ASC) moieties with dynamic reversibility and multiple hydrogen bonding were disclosed and used to prepare transparent, high modulus, and malleable polymer networks. It was found that the ASC moiety can reversibly generate isocyanate and hydrazide at elevated temperatures, that is, exhibiting dynamic reversibility. ASC can also produce the disordered multiple hydrogen bonds that contribute to superior mechanical strength for dynamic polymers. The hydrogen bonding in ASC moieties can diminish the energy barrier for the cleavage of dynamic covalent bonds, and the dissociation of ASC moieties further promotes the disruption of hydrogen bonds, showing the synergistic dynamic effects. ASC moieties provide a valuable molecular engineering opportunity toward high-performance dynamic polymer materials. The polymer containing ASC moieties possesses excellent optical transparency, superb mechanical performance (Young's modulus up to 1.7 GPa), together with malleable and healing properties.

The transition toward renewable energy sources requires low-cost, efficient, and durable electrocatalysts for green H

Liquid crystal elastomers (LCEs), a class of soft materials capable of a large and reversible change in the shape under the trigger of external stimuli, can be fabricated into diverse architectures with complicated deformation modes through four-dimensional (4D) printing. However, the printable LCE ink is only in the form of monomeric precursors and the deformation mode is limited to contraction/extension deformation. Herein, we report a novel approach to break through these limitations. We achieved 4D printing of a single-component liquid crystal polymer ink in its isotropy state through direct ink writing (DIW) technology. The drawing force imposed by the movement of nozzle in the extruded printing process was able to align the mesogen units along the specific printing path. An orientation gradient perpendicular to the printing direction was obtained due to the existence of a temperature gradient between the two sides of printed samples and could be further fixed by post-photo-cross-linking treatment through the dimerizable groups in the LCE, realizing a new actuation mode in the field of extrusion-based printing of LCE actuators. The printed film was able to change reversibly from a strip to a tightly hollow cylinder and could reversibly lift up an object with roughly 600 times its own weight. The orientation gradient can be patterned through liquid-assistant printing or programmed structure design to integrate both bending and contraction actuation modes on the same printed sample, leading to complex deformation and two-dimensional (2D) planar porous structure to three-dimensional (3D) porous cylinder transition. This study opens up a new prospect to directly print a wide variety of LCE actuators with versatile actuation modes.

Stimuli-responsive structurally dynamic polymers are capable of mimicking the biological systems to adapt themselves to the surrounding environmental changes and subsequently exhibiting a wide range of responses ranging from self-healing to complex shape-morphing. Dynamic self-healing polymers (SHPs), shape-memory polymers (SMPs), and liquid crystal elastomers (LCEs), which are three representative examples of stimuli-responsive structurally dynamic polymers, have been attracting broad and growing interest in recent years because of their potential applications in the fields of electronic skin, sensors, soft robots, artificial muscles, and so on. Recent advances and challenges in the developments toward dynamic SHPs, SMPs, and LCEs are reviewed, focusing on the chemistry strategies and the dynamic reaction mechanisms that enhance the performances of the materials including self-healing, reprocessing, and reprogramming. The different dynamic chemistries and their mechanisms on the enhanced functions of the materials are compared and discussed, where three summary tables are presented: A library of dynamic bonds and the resulting characteristics of the materials. Finally, a critical outline of the unresolved issues and future perspectives on the emerging developments is provided.

Conductive silicone elastomer carbon nanotubes (CNTs) composites possess potential applications in a variety of fields, including electronic skin, wearable electronics, and human motion detection. ...

A flexible, wearable electronic device composed of magnetic iron oxide (Fe3O4)/reduced graphene oxide/natural rubber (MGNR) composites with a segregated network was prepared by electrostatic self-assembly, latex mixing, and in situ reduction. The segregated network offers the composites higher electrical conductivity and more reliable sensing properties. Moreover, the addi-tion of Fe3O4 provides the composites with better electromagnetic interference shielding effectiveness (EMI SE). The EMI shielding property of MGNR composites is more stable under tensile deformation and long-term cycling conditions and has a higher sensitivity to stretch strain compared with the same structure made from reduced graphene oxide/natural rubber (GNR) composites. The EMI SE value of MGNR composites reduces by no more than 2.9% under different tensile permanent deformation, cyclic stretching, and cyclic bending conditions, while that of GNR composites reduces by approximately 16% in the worst case. Additionally, the MGNR composites have a better sensing performance and can maintain stable signals, even in the case of cyclic stretching with a very small strain (0.05%). Furthermore, they can steadily monitor the changes in resistance signals in various human motions such as finger bending, wrist bending, speaking, smiling, and blinking, indicating that the MGNR composites can be used in future wearable electronic flexibility devices.

Despite recent progress in graphene-based aerogels, challenges such as low mechanical strength and adsorption efficiency are still remaining. Here the reduced graphene oxide (rGO)/chitosan (CS) composite aerogel microspheres (rGCAMs) with center-diverging microchannel structures were developed by electrospraying and freeze-drying method. The optimized rGCAMs exhibit a high Young's modulus of 197 kPa and can support ~75,000 times its own weight, due to the cross-linking of CS by glutaraldehyde. Meanwhile, the rGCAMs can maintain high adsorption capacity for 15 cyclic tests due to its excellent mechanical strength. The oil adsorption kinetics and isotherms of rGCAMs follow the pseudo-second-order kinetic equation and the Langmuir model, respectively. The whole adsorption process is influenced by the oil diffusion in the liquid matrix and also in the intra-particle of aerogel microspheres. Moreover, rGCAMs can also be used to separate both surfactant-stabilized water-in-oil and oil-in-water emulsions through demulsification. The high-strength, recyclable and separation-efficient rGCAMs can be a potential candidate for oily wastewater treatment.

The simultaneous reduction and functionalization of graphene oxide (GO) was achieved through a chemical grafting reaction with cystamine dihydrochloride (CDHC), a novel functional agent with dynamic disulfide bond. CDHC-reduced GO (CGO) can be uniformly and stably dispersed in the aqueous phase. Furthermore, CGO reinforced styrene-butadiene rubber (SBR) composites with highly filled silica content were prepared by a latex mixing and coagulation process. TEM confirmed both CGO and silica can be uniformly dispersed in the rubber matrix. The dynamic disulfide bonds of the grafted CDHC in the CGO can participate in the subsequent vulcanization of SBR rubber through disulfide exchange reactions, thereby forming a tight interaction between GO and rubber. Compared with normally reduced GO system, the mechanical and thermal properties of CGO-containing rubber nanocomposites were significantly improved. The results show that CGO is effective to reinforce rubber composites, which has the potential to be used for tire rubber materials.

Chitosan (CS) aerogels were prepared by freeze-drying as potential adsorbents for water purification, and the effect of the strategy of crosslinking was investigated by varying the amount of crosslinker (glutaraldehyde) and the sequence of steps for the preparation of the aerogel. Two procedures were compared, in which the crosslinking step was carried out before or after the freeze-drying of the starting CS solution. When crosslinking was postponed after the freeze-drying step, the adsorption capacity towards an anionic dye, such as indigo carmine, considerably increased (up to +45%), reaching values as high as 534.4 ± 30.5 mg g−1. The same crosslinking strategy ensured a comparable improvement also in nanocomposite aerogels containing graphene oxide (GO), which was added to enhance the mechanical strength and provide adsorption capacity towards cationic dyes. Besides possessing good mechanical strength (compressive modulus higher than 1 MPa), the CS/GO aerogels were able to bind also cationic pollutants such as methylene blue. The maximum uptake capacity increased from 4.3 ± 1.6 to 168.6 ± 9.6 mg of cationic dye adsorbed per gram of adsorbent with respect to pristine CS aerogels.

Menglong Liu,1 Tengfei Liu,1 Xiaorong Zhang,1 Zhiwen Jian,2 Hesheng Xia,2 Jiacai Yang,1 Xiaohong Hu,1 Malcolm Xing,1,3 Gaoxing Luo,1 Jun Wu1,41Institute of Burn Research, State Key Laboratory of Trauma, Burn and Combined Injury, Southwest Hospital, Third Military Medical University (Army Medical University), Chongqing 400038, People’s Republic of China; 2State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu, 610065, People’s Republic of China; 3Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB R3T 2N2, Canada; 4Department of Burns, the First Affiliated Hospital, SunYat-Sen University, Guangzhou 510080, People’s Republic of ChinaBackground: Designing a wound dressing that effectively prevents multi-drug-resistant bacterial infection and promotes angiogenesis and re-epithelialization is of great significance for wound management.Methods and results: In this study, a biocompatible composite membrane comprising biomimetic polydopamine-modified eggshell membrane nano/microfibres coated with KR-12 antimicrobial peptide and hyaluronic acid (HA) was developed in an eco-friendly manner. The physicochemical properties of the composite membrane were thoroughly characterized, and the results showed that the surface hydrophilicity and water absorption ability of the composite membrane were improved after the successive conjugation of the HA and the KR-12 peptide. Furthermore, the in vitrobiological results revealed that the composite membrane had excellent antibacterial activity against Gram-positive Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative Escherichia coli, and it could prevent MRSA biofilm formation on its surface. Additionally, it promoted the proliferation of keratinocytes and human umbilical vein endothelial cells and increased the secretion of VEGF. Finally, an in vivo animal study indicated that the composite membrane could promote wound healing via accelerating angiogenesis and re-epithelialization, which were demonstrated by the enhanced expression of angiogenetic markers (CD31 and VEGF) and keratinocyte proliferation marker (PCNA), respectively.Conclusion: These results indicated that the composite membrane is a potential candidate of wound dressingsKeywords: antimicrobial peptides, hyaluronic acid, fibrous eggshell membrane, antibacterial activity, angiogenesis, re-epithelialization

In the last decade, a great deal of research has been devoted to the design and development of graphene-based polymer nanocomposites characterized by a prescribed arrangement of the graphene-based nanosheets into spatially segregated 3D architectures. The formation of a continuous filler network obtained by confining the nanosheets into a constrained volume of the polymeric matrix is particularly attractive from a technological point of view. The preparation of segregated 3D graphene-based architectures facilitates the proper tailoring of the overall performance of the resulting polymer nanocomposites, providing significant improvements in terms of structural (i.e., mechanical properties) and functional (electrical properties, sensing ability, and adsorption/absorption capacity) features. This review focuses on polymer-based nanocomposites in two categories, namely bulk and porous (foam and aerogels) systems. These all share the common distinctive feature that relies on the peculiar arrangement of the graphene-based nanosheets in the form of a segregated yet continuous 3D assembly. For each class of materials, the main preparation strategies are presented and the resulting structure-property correlations are highlighted and discussed, together with the technological implications, and possible future directions.

Highly sensitive conductive polymer composites for piezoresistive sensing are developed by a design of the formulation variables of extrusion-based manufacturing (filler type/amount, polymer amount) and annealing (a), considering thermoplastic polyurethane (TPU) and/or olefin block copolymer (OBC) as polymer matrix and carbon black (CB) as conductive filler. With ternary composites - based on a CB type with stronger filler-matrix interactions and an appropriate OBC/TPU blend mass ratio (40/60 with CB amount of 5–10 m%; 50/50 with CB amount of 10 m%), the challenging region of both high sensitivity and static strain (maximal gauge factors (GFmax) > 50 and emax > 100%) can be realized: GFmax > 104 and emax = 20–240%. OBC binary composites with a high CB2 amount (e.g. 15 m%) are however needed for ultrahigh static strains (emax > 600%). Well-designed ternary composites (e.g. OBC40-CB/TPU60-7-a and OBC30-CB/TPU70-7-a) possess a large dynamic resistance change, negligible hysteresis and high stability and display strain sensor application potential. Highly CB2 loaded binary (≥12 m%) and ternary composites (10 m%) exhibit a more obvious strain-dependent dynamic hysteretic behavior, as they switch from a dual peak to single peak pattern toward the sensing strain limit, which is interesting for self-diagnose.

Atom transfer radical polymerization (ATRP) has been previously mediated by ultrasound using a low concentration of copper complex in water (sono-ATRP) or by addition of piezoelectric materials in organic solvents (mechano-ATRP). However, these procedures proceeded slowly and yielded polymers contaminated by new chains initiated by hydroxyl radicals or by residual piezoelectrics. Unexpectedly, in the presence of sodium carbonate, rapid sono-ATRP of methyl acrylate in DMSO was achieved (80% conversion in

Anisotropic aerogel-foam composites were developed by embedding a reduced graphene oxide (rGO)/chitosan aerogel directly into an open-cell polyurethane foam through an in situ bidirectional freeze-drying process. The resulting aerogel-foam composites possess both excellent compression-resilience performance and stable piezo-resistive properties due, respectively, to the excellent mechanical properties of polyurethane foams and to the presence of a chitosan-based aerogel loaded with rGO. The latter, indeed, provides outstanding electrical properties due to its conductive and parallel flat lamellar structure. It has been proven that both mechanical and piezo-resistive properties are stable even after 1000 loading/unloading cycles and a reduction of the electrical resistance of about 86% is observed upon the application of a 60% strain. The high sensitivity, long cycling life, and reliable performance over a wide strain range make this unique anisotropic aerogel-foam composite a highly promising candidate for the production of wearable sensors and healthcare monitoring devices.

Self-healing polymer materials have drawn rapidly increasing interest over the last decade, and have been studied and used in an ever-increasing range of applications. Herein, we successfully make the covalent urea bond – a pinnacle of stability due to strong resonance effects – dynamic in nature through mediation of zinc salts. The dynamic covalent character of urea in the presence of zinc ions is confirmed through dissociation reaction experiments and quantum chemical calculations of small-molecule model urea compounds. In line with our experiments, the modelling results suggest that the presence of zinc ions speeds up the reaction of urea dissociation by two orders of magnitude via the formation of O-bound Zn complexes. Based on such dynamic covalent urea bonds, we then develop a novel class of self-healing polymer materials with excellent healing efficiencies. Different kinds of self-healing and reprocessable polyurea materials were prepared, with polymer properties that can be easily tuned by varying the degree of crosslinking and the molecular weight of the siloxane precursor. Since different kinds of self-healing polyurea materials could easily be prepared due to the commercial availability of a very wide range of amine and isocyanate monomers, this introduction of self-healing properties is expected to have significant potential in a range of applications, such as coatings, paints, and 3D printing. In addition, this introduces polyureas and other urea-containing polymers as a class of highly stable, yet easily reprocessable plastics, which is highly relevant given the globally desired more sustainable use of plastics.

Significant advances have been made in the development of self-healing synthetic polymer materials in recent years. This review article discusses the recent progress in preparation, characterization and properties of different kinds of intrinsic self-healing elastomers based on reversible covalent bonds and dynamic supramolecular chemistry. Healing conditions, mechanical property recovery and healing efficiency are the main discussion topics. Potential applications, challenges and future prospects in self-healing elastomer fields are also discussed in the last part of this review.

High-intensity Focused Ultrasound (HIFU) was used to stimulate the embedded copper sulfate (CuSO4) particles to release from the crosslinked poly (methyl methacrylate-co-butyl acrylate) copolymer solid matrix. In order to better understand the ultrasound release mechanism for drug/polymer delivery systems, the synchrotron radiation X-ray computed microtomography (SR-CT) was used to non-destructively investigate the structure of drug/polymer delivery systems after different HIFU treatment time. For the first time, we clearly demonstrate that ultrasonic waves can overcome the constraints of the polymer chain and drive the filler to move from the strong region to the weak region in the solid polymer matrix, thus resulting in a change in distribution of the filler in solid polymers. This result also demonstrates that SR-CT is a powerful technique which can be used to quantitatively study the 3D structure of fillers/polymers composite as it can take a broader and overall view than the conventional localized two-dimensional analysis method such as SEM, TEM.

Superhydrophobic, flexible, and ultrahigh-performance electromagnetic interference (EMI) shielding papers are of paramount importance to safety and long-term service under external mechanical deformations or other harsh service environments because they fulfill the growing demand for multipurpose materials. Herein, we fabricated multifunctional papers by incorporating sputter-deposited nickel nanoparticles (NiNPs) and a fluorine-containing coating onto cellulose filter papers coated with silver nanowires (AgNWs). AgNW networks with sputter-deposited NiNPs provide outstanding magnetic properties, electrical conductivity, and EMI shielding performance. At an AgNW content of 0.109 vol % and a NiNP content of 0.013 mg/cm2, the resultant papers exhibit a superior EMI shielding effectiveness (SE) of 88.4 dB. Additionally, the fluorine-containing coating endows the resultant papers with a high contact angle of 149.7°. Remarkably, the obtained papers still maintain a high EMI SE even after 1500 bending cycles or immersion in water, salt, or strong alkaline solutions for 2 h, indicating their outstanding mechanical robustness and chemical durability. This work opens a new window for designing and implementing ultrahigh-performance EMI shielding materials.

Self-healing coatings that are able to self-repair after being damaged represent an effective solution to provide a reliable and long-lasting protection of the underlying substrate. In this work, we developed self-healing waterborne polyurethane (PU) coatings through the introduction of Diels-Alder bonds in the polymer backbone. Although heat is typically used as trigger, here we exploited photothermal converters to allow also NIR light-induced self-healing. To this aim, we synthesized (3-aminopropyl)-triethoxysilane-modified graphene oxide nanosheets that were subsequently coated by nanometric polydopamine particles, which serve for imparting to the coating the NIR-responsive self-healing feature. Fourier transform infrared and X-ray photoelectron spectroscopy confirmed the successful synthesis of PDA-coated reduced graphene oxide nanoparticles, which were thus exploited to prepare nanocomposite PU coatings on bronze substrates on which they exhibited good adhesion. Once scratched, fast and effective self-healing was ensured upon irradiation with NIR light for only 30 s. In addition, electrochemical impedance spectroscopy analyses proved that the nanocomposite coatings exhibited improved barrier properties which resulted in an enhanced protection of the underlying metal from corrosion.

Organic coatings are extensively investigated as possible solution to prevent or at least retard the occurring of corrosion processes on metal surfaces. Their actual breakthrough is still hampered by the risk of barrier properties loss because of local failure of the coating integrity. To address this issue, self-healing coatings, which are intrinsically able to recover from damages upon exposure to external stimuli, are currently gaining increasing attention. Herein, waterborne polyurethanes (PU) are synthesized, and a Diels-Alder adduct is added into the polymeric backbone to endow the material with self-healing functionality. The effect of different diisocyanate in PU synthesis is explored, namely isophorone diisocyanate, 4,4 '-dicyclohexylmethane diisocyanate (HMDI), and hexamethylene diisocyanate. The obtained results highlight the key role of the interactions among soft and hard segments in ultimately defining the coating performances. Actually, the combination of Fourier transform infrared spectroscopy, atomic force microscopy and X-ray diffration analysis reveals that the HMDI-based PU have showed the best balance in terms of H-bonding strength among hard segments and crystallinity degree in the soft ones. This allows to reach a good compromise in terms of mechanical resistance, anticorrosion properties, and self-healing ability.

The electromagnetic properties of structures with spatially periodic distributed graded refractive index were investigated in the terahertz frequency range. The band structure and electromagnetic response of material with harmonically distributed refractive index were calculated and analyzed. The analytical expressions for frequencies of the first and second bandgap are derived. 3D printed gyroid based architectures were proven to be harmonically graded refractive index structures with designed bandgaps in THz frequency ranges. The transmission coefficient of thermoplastic polyurethane-based samples were experimentally measured in the frequency range 100–500 GHz and compared with theoretical results. Due to losses in the real world produced samples, the predicted response is significantly dumped in the terahertz range and only traces of band gaps are experimentally observed. This funding paves the way toward a new generation of 3D printed THz components for gradient-index optics applications.

Improving the adsorption capacity of the adsorbent and realizing rapid separation are quite important for water treatment. Herein, one kind of novel Ni/Co-contained reduced graphene oxide aerogel microspheres (rGOAMs-M) with high surface area and magnetic response are synthesized by a novel process comprised of electrospraying, droplets spherification, crosslinking immobilizing of metal, lyophilization and thermal reduction. The aqueous dispersion mixture of graphene oxide and sodium alginate is electrosprayed under high electric voltages to produce droplets, which are collected in a nickel/cobalt acetate tetrahydrate solution and then crosslinked between alginate and metal ions. The obtained rGOAMs-M have the cabbage-like inner structures, and possess the organic solvent/oil adsorption capacities of 107–270 g.g−1 and also extraordinary oil/water emulsion separation ability. The rGOAMs-M also can be rapidly assembled and separated from the medium under a magnetic field.

Multifunctional polymer composites with anisotropic properties are attracting interests as they fulfil the growing demand of multitasking materials. In this work, anisotropic polymer composites are fabricated by combining the layer-by-layer (LBL) filtration method with the alternative assembling of carbon nanotubes (CNTs) and hexagonal boron nitride flakes (hBN) on natural rubber latex particles (NR). The layered composites exhibit anisotropic thermal and electrical conductivities, which are tailored through the layer formulations. The best composite consists of four layers of NR modified with 8 phr (parts per Hundred Rubber) CNTs (~7.4 wt%) and four alternated layers with 12 phr hBN (~10.7 wt%). The composites exhibit an electromagnetic interference (EMI) shielding effectiveness of 22.41+-0.14 dB mm-1 at 10.3 GHz and a thermal conductivity equal to 0.25 W/(mK). Furthermore, when the layered composite is used as an electrical thermal heater the surface reaches a stable temperature of ~103 C in approx. 2 min, with an input bias of 2.5 V., 13 pages, 5 figures

Aiming at the development of a controlled redox responsive polymeric micelle system, a series of redox-sensitive ABA triblock degradable copolymers with different amounts of disulfide bonds were synthesized. These multi-disulfide-containing amphiphilic copolymers are able to self-assemble in aqueous solution to form spherical micelles with a hydrophobic polyurethane block forming the hydrophobic core. The presence of dynamic and labile disulfide bonds in the copolymer makes the copolymer and its micelle have responsivity to stimuli such as redox agents and ultrasound. The micellar properties and release kinetics of encapsulated guest molecules in response to stimuli were investigated using hydrophobic pyrene as a fluorescent probe and DTT as a redox agent. The redox-responsive behavior could be adjusted by changing the amount of disulfide bonds within the copolymer backbone. A relatively fast release behavior was observed for micelles formed by the copolymers in which every repeat unit of the hydrophobic block contains a disulfide bond. Furthermore, the release rate could be greatly enhanced and adjusted remotely under HIFU irradiation in the presence of DTT. The HIFU/redox combined stimulus for the specially designed copolymer micelles containing disulfide bonds provides a novel modality for drug delivery systems.

A three-dimensional graphene (GE) segregated network structure is of significance for improving the conductivity of composites. However, constructing such a GE network structure in composites still remains a challenge. Here, we demonstrate a facile process, that is, liquid-phase redispersion and self-assembly (LRS) to prepare polymer nanocomposites with graphene segregated networks. High shear liquid-phase mixing accompanied by the diffusion of dissolved polymer chains into the interstices and voids of the loose graphene powders can lead to redispersion of GE in polymer solution. Once the stirring is stopped, the self-assembly and segregation of redispersed GE occurs in a poor solvent driven by π-π interaction. After solvent evaporation, the GE assembly structures are retained as networks in the GE/polymer composite prepared by hot pressing. The graphene/(isobutylene-isoprene rubber) nanocomposite (GE/IIR) was investigated as a demonstration for the advantages of the LSR method. The morphologies of GE assemblies in the liquid phase and GE networks in the solid composite were observed. Due to the existence of the homogeneously distributed graphene segregated networks, the tensile strength and elongation at break for GE/IIR nanocomposites increase by ∼410 and ∼126%, respectively, and the electrical conductivity reaches ∼100 S m-1 at a GE content of 3.76 vol %. The LRS method was also successfully tried for systems with different polymer matrixes and different solvents, suggesting the robustness of the proposed method. The prepared flexible GE/IIR nanocomposites with GE networks are sensitive to tiny strain and can be applied in wearable sensors for the detection of human physiological signals.

An amphiphilic metallo-supramolecular poly(propylene glycol)-block-poly(ethylene glycol) block copolymer containing a bis(2,2':6',2″-terpyridine) ruthenium (II) complex as a supramolecular connection between the two constituting blocks was used to prepare stable aqueous micelles which displayed a high intensity focused ultrasound (HIFU) triggered release behavior. By adjusting the HIFU time and intensity, the novel modality of HIFU triggered release allows for fine-tuning of the release kinetics of the encapsulants from the micelles in a remote and controlled way. Nuclear magnetic resonance spectroscopy, ultraviolet spectroscopy, and matrix-assisted laser desorption/ionization-time of flight mass spectrometry confirmed that the degradation of the micelles was due to the cleavage of the ether bond connected to the pyridine ring. This well controlled HIFU-copolymer micelle drug delivery system has considerable potential in targeted therapy.

MXene/polymer composites have been used as electromagnetic interference (EMI) shielding materials due to metallic conductivity of MXene recently. Considering the biodegradability, nontoxic effects and renewable nature of biomass polymer, chitosan (CS)/MXene films with an EMI shielding function were prepared by vacuum assisted filtration. The well-aligned Ti3C2Tx layers endow CS/MXene films with excellent electrical conductivity, which is association with air humidity, and EMI shielding property. The 37-micron-thick CS/MXene film at a T3C2Tx content of 75 % exhibits a high EMI shielding effectiveness of ∼ 34.7 ± 0.2 dB due to the excellent electrical conductivity of CS/MXene films (∼ 1402 ± 70 S m-1) and multiple internal reflections of Ti3C2Tx flakes. Moreover, the specific shielding effectiveness of 13-micron-thick CS/MXene film at a T3C2Tx content of 50 % reaches to 15153.9 ± 153 dB cm-1, outperforming the reported biomass-based EMI shielding composites in the X-band frequency. Due to these advantages, the film shows potential applications in the next-generation EMI shielding materials.

Self-healing antifouling materials have gained rapidly increasing interest over the past decade and have been studied and used in a rapidly increasing range of applications. Recent developments and challenges in self-healing antifouling materials are summarized in four sections: first, the different mechanisms for both antifouling and self-healing are briefly discussed. Second, three main categories of self-healing antifouling materials based on surface replenishing and dynamic covalent and noncovalent interactions are discussed, with a focus on the preparation, characterization, and central characteristics of different self-healing antifouling materials. Third, different types of potential applications of self-healing antifouling materials are summarized, such as injectable hydrogels and oil/water separations. Finally, a summary of future development of the field is provided, and a number of critical limitations that are still outstanding are highlighted.

Selective laser sintering (SLS) is a powder-based additive manufacture technology that uses energy provided by the laser to melt and fuse the powders and then stack layer by layer to form a printed part based on 3D model data. The powder quality significantly affects the performance of SLS sintered parts and thus the powder design and preparation is the core technology for SLS. This chapter introduces the powder sintering fundamental for SLS, as well as the intrinsic and extrinsic properties of polymer powders and their effects on the properties of sintered parts. The research on the electric conductive composite powders for SLS was mainly reviewed. The effect of powder preparation methods, fillers and polymers type on the formation of conductive segregation networks was discussed.

In many fused filament fabrication (FFF) processes, commercial printers are used, but rarely are printer settings transferred from one commercial printer to the other to give similar final tensile part performance. Here, we report such translation going from the Felix 3.0 to Prusa i3 MK3 printer by adjusting the flow rate and overlap of strands, utilizing an in-house developed blend of polylactic acid (PLA) and poly(butylene adipate-co-terephthalate) (PBAT). We perform a sensitivity analysis for the Prusa printer, covering variations in nozzle temperature, nozzle diameter, layer thickness, and printing speed (Tnozzle, dnozzle, LT, and vprint), aiming at minimizing anisotropy and improving interlayer bonding. Higher mass, larger width, and thickness are obtained with larger dnozzle, lower vprint, higher LT, and higher Tnozzle. A higher vprint results in less tensile strain at break, but it remains at a high strain value for samples printed with dnozzle equal to 0.5 mm. vprint has no significant effect on the tensile modulus and tensile and impact strength of the samples. If LT is fixed, an increased dnozzle is beneficial for the tensile strength, ductility, and impact strength of the printed sample due to better bonding from a wider raster structure, while an increased LT leads to deterioration of mechanical properties. If the ratio dnozzle/LT is greater than 2, a good tensile performance is obtained. An improved Tnozzle leads to a sufficient flow of material, contributing to the performance of the printed device. The considerations brought forward result in a deeper understanding of the FFF process and offer guidance about parameter selection. The optimal dnozzle/vprint/LT/Tnozzle combination is 0.5 mm/120 mm s&minus, 1/0.15 mm/230 &deg, C.