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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.

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.

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.

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.

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.

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

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.

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.

Although shape-memory polymers (SMPs) can alter their shapes upon stimulation of environmental signals, complex shape transformations are usually realized by using advanced processing technologies (four-dimensional printing) and complicated polymer structure design or localized activation. Herein, we demonstrate that stepwise controlled complex shape transformations can be obtained from a single flat piece of SMP upon uniform heating. The shape-memory blends prepared by solution casting of poly(ethylene oxide) and poly(acrylic acid) (PAA) exhibit excellent mechanical and room-temperature shape-memory behaviors, with fracture strain beyond 800% and both shape memory and shape recovery ratio higher than 90%. After plastic deformation by stretching under ambient conditions, the material is surface-patterned to induce the formation of an Fe3+-coordinated PAA network with gradually altered cross-linking density along the thickness direction at desired areas. Upon subsequent heating for shape recovery, strain r...

Rapid absorption of wound exudate and prevention of wound infection are prerequisites for wound dressing to accelerate wound healing. In this study, a novel kind of promising wound dressing is developed by incorporating polyhexamethylene guanidine (PHMG)-modified graphene oxide (mGO) into the poly(vinyl alcohol)/chitosan (PVA/CS) matrix, conferring the dressing the required mechanical properties, higher water vapor transmission rate (WVTR), less swelling time, improved antibacterial activity, and more cell proliferation compared to the PVA/CS film crosslinked by genipin. In vivo experiments indicate that the PVA/CS/mGO composite film can accelerate wound healing via enhancement of the re-epithelialization. PVA/CS/mGO composite film with 0.5 wt% mGO sheets displays the best wound healing properties, as manifested by the 50% higher antibacterial rate compared to GO and the wound healing rate of the mouse using this dressing is about 41% faster than the control group and 31% faster than the pure PVA/CS dressing. The underlying mechanism of the accelerated wound healing properties may be a result of the improved antibacterial ability to eradicate pathogenic bacteria on the wound area and maintain an appropriate moist aseptic wound healing environment to accelerate re-epithelialization. These findings suggest that this novel composite PVA/CS/mGO film may have promising applications in wound dressing.

A pH- and ultrasound dual-responsive drug release pattern was successfully achieved using mesoporous silica nanoparticles (MSNs) coated with polydopamine (PDA). In this paper, the PDA shell on the MSN surface was obtained through oxidative self-polymerization under the alkaline condition. The morphology and structure of this composite nanoparticle were fully characterized by a series of analyses, such as infrared (IR), transmission electron microscopy, and thermogravimetric analysis. Doxorubicin hydrochloride (DOX)-loaded composite nanoparticles were used to study the performances of responsive drug storage/release behavior, and this kind of hybrid material displayed an apparent pH response in DOX releasing under the acidic condition. Beyond that, upon high-intensity focused ultrasound exposure, loaded DOX in composite nanoparticles was successfully triggered to release from pores because of the ultrasonic cavitation effect, and the DOX-releasing pattern could be optimized into a unique pulsatile fashion by switching the on/off status. From the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, it was observed that our blank nanoparticles showed no toxicity to HeLa cells, but DOX-loaded nanoparticles could inhibit the growth of tumor cells. Furthermore, these composite nanoparticles displayed an effective near-IR photothermal conversion capability with a relatively high conversion efficiency (∼37%). These as-desired drug delivery carriers might have a great potential for future cancer treatment that combine the chemotherapy and photothermal therapy.

Flexible natural rubber/magnetic iron oxide (Fe3O4)@reduced graphene oxide (NRMG) composites with segregated structure were prepared by a self-assembly method in latex. Various characterization techniques were employed to verify the successful preparation of Fe3O4@rGO and the formation of segregated structure within the bulk composites. Compared with natural rubber/reduced graphene oxide (NRG) composites, the presence of Fe3O4 enhances the electromagnetic interference shielding effectiveness (EMI SE) of NRMG composites. The EMI SE value of NRMG composite with 10 phr (part per hundred parts of rubber) rGO is 1.4 times higher than that of NRG composite with the same rGO content in the frequency range of 8.2–12.4 GHz. The specific EMI SE of NRMG composite reaches 26.4 dB mm−1, outperforming the ever-reported polymer/Fe3O4@rGO composites with low rGO content. Excitingly, the EMI SE of NRMG composite decreases only 3.5% even after 2000 bending-release cycles, demonstrating potential applications in flexible shielding materials.

A new kind of fast near-infrared (NIR) light-responsive shape-memory polymer composites was prepared by introducing polydopamine particles (PDAPs) into commercial shape-memory polyurethane (SMPU). The toughness and strength of the polydopamine-particle-filled polyurethane composites (SMPU-PDAPs) were significantly enhanced with the addition of PDAPs due to the strong interface interaction between PDAPs and polyurethane segments. Owing to the outstanding photothermal effect of PDAPs, the composites exhibit a rapid light-responsive shape-memory process in 60 s with a PDAPs content of 0.01 wt%. Due to the excellent dispersion and convenient preparation method, PDAPs have great potential to be used as high-efficiency and environmentally friendly fillers to obtain novel photoactive functional polymer composites.

A series of chemically treated graphene oxide (GO) samples, destined for the preparation of several composite materials, was studied by X-ray photoelectron spectroscopy (XPS). From their comparison, the 3-mercaptopropyl trimethoxysilane was identified as the most effective reducing agent among the used procedures. The influence of ultrahigh vacuum annealing up to 600°C on the chemical composition and carbon electronic configuration in reduced GO samples was further investigated by XPS and Auger electron spectroscopy. All the samples before and after thermal treatments were analyzed in situ by XPS and Auger electron spectroscopy, paying a particular attention to the shape of C KVV spectra described by the values of D parameter. The changes of chemical composition and carbon configuration reflected in the D parameter revealed the full reduction of GO to graphene after annealing in ultrahigh vacuum at 600°C. The successful reduction of GO to graphene was also confirmed by Raman spectroscopy. Obtained bulk samples of graphene aggregates remained stable in air, testifying the irreversibility of this reduction.

A new kind of ultrafast near-infrared light responsive shape memory assisted self-healing polymer composite was prepared by introducing polydopamine particles (PDAPs) into polyurethane containing Diels–Alder bonds. The mechanical properties of the polyurethane composites are significantly enhanced with the addition of PDAPs due to the strong interface interaction between PDAPs and polyurethane segments. Owing to the outstanding photothermal effect of PDAPs and excellent dynamic properties of Diels–Alder bonds, the composites possess rapid light responsive shape memory and self-healing properties. The shape memory ability of the materials also plays an important role in improving the self-healing efficiency. Due to the excellent dispersion and easy preparation method, PDAPs have great potential to be used as high-efficiency and environmentally friendly fillers to obtain novel photoactive functional polymer composites.

Herein, we show for the first time drop-casting zwitterionic polymer colloidal particles onto different surfaces to obtain zwitterionic coatings with highly protein-repelling properties and dual self-healing capabilities. Upon nano/micro mechanical scratches, the coatings self-heal in a NaCl solution which is accompanied by the recovery of the anti-biofouling characteristics. Also under severe macro damage conditions, water will induce the zwitterionic groups buried inside the particles to transfer to the coating surface, and as such regenerate the surface-wetting properties and repair the anti-biofouling properties.

Endowing thermoset polymer materials with self-healing and recyclable properties by incorporating dynamic bonds into the polymer networks is of vital realistic significance. However, such materials are still limited because of the difficult synthetic process and expensive dynamic monomers or environment-unfriendly catalysts. Herein, catalyst-free and colorless transparent healable and recyclable poly(oxime-urethane) elastomers based on dynamic oxime–carbamate bonds were developed with scaling-up capability using low-cost and commercially available compounds. These materials display remarkable comprehensive properties and relatively low relaxation activation energy (∼29.7 kcal mol−1) which results in excellent healable and recyclable performance. The poly(oxime-urethane) with a crosslink density ν of ∼0.2 mmol cm−3 possesses a tensile strength of ∼13.5 MPa, a breaking strain of ∼812%, toughness up to ∼40 MJ m−3, an excellent elastic recovery of ∼90% and an average optical transmittance of ∼86% in the visible range. This material can be completely healed at 110 °C in 0.5 h. In situ structural characterizations revealed that the dynamic properties originate from the reversibility of oxime–carbamate bonds and hydrogen bonds.

Graphene aerogels featuring ordered and controllable architectures represent promising candidates for use in water purification. In this context, a unique method for directing the self-assembly of graphene oxide (GO) nanoplatelets in a sodium hydrogen sulfite (NaHSO 3 ) aqueous suspension is proposed, which leads to the formation of annular GO assemblies and ultimately turns into graphene millimeter-vortex ring (GMVR) aerogel after chemical reduction and freeze-drying process. In comparison to other spherical or cylindrical adsorbents, GMVR exhibits superior adsorption efficiency for the removal of contaminants, such as dyes and other organic solvents from wastewater. Particularly, the maximum adsorption capacity of GMVR for methylene blue was 1004 mg g −1 , which is much higher than that of conventional graphene-based materials. The remarkable absorbability of GMVR materials is closely related to their increased surface area as well as the shortened diffusion pathway. Such approach of preparing GMVR composites provides potential route for the future development of excellent adsorbents.

Electromagnetic interference (EMI) shielding foams featuring light weight and ultralow thermal conductivity have received attention in a diverse range of applications, but their limited service life makes them very challenging in realistic use. As such, prolonging their service life has aroused significant scientific and technical interest. Herein, we report a facile method to prepare a carbon nanotube/acrylic copolymer (CNT/AC) foam by using isobutane as a blowing agent. This strategy is effective in constructing a 3D porous architecture composed of a segregated CNT network impregnated with an AC polymer through a hot pressing foaming process. This unique structure endows the composite with superior EMI specific shielding effectiveness (for foams with 0.62 vol% CNTs: 1243.3 dB·cm2·g−1) and an extremely low percolation threshold and thermal conductivity (0.008 W·m−1·K−1). More intriguingly, the inherent long-chain entanglements give the foam a self-healing feature. Specifically, with the incorporation of 0.80 vol% CNTs, the healing effectiveness of the EMI shielding performance is greater than 79% in the frequency range from 8.2 GHz to 12.4 GHz. Overall, the resulting CNT/AC foam possesses numerous advantages such as light weight, thermal insulation and EMI shielding self-healing performance, suggesting great potential application value in aviation areas.

Polydimethylsiloxane (PDMS) elastomer is one of most investigated and pioneering 3D printing materials. However, the powder-based 3D printing remains a big challenge due to the thermoset intrinsic character of PDMS. Here we realized the powder-based selective laser sintering (SLS) 3D printing of PDMS elastomer based on one kind of novel self-designed PDMS covalent adaptable networks (CANs) containing hindered pyrazole urea dynamic bonds. The dynamic chemical mechanism of the hindered pyrazole urea bonds is confirmed by small molecule models experiments, density functional theory calculation, and also stress relaxation analysis. The electron-donating large steric hindrance substituent in the pyrazole ring was found to effectively promote the dynamic character of pyrazole urea bond. The PDMS CANs show excellent self-healing and reprocessing properties. Furthermore, kilo-scale PDMS powders were prepared by cryogenic grinding and the powder morphology was optimized for SLS 3D printing. A PDMS insole with complex structure designed based on the personalized foot pressure distribution data was printed, and the foot orthotic and self-healing functions for the insole were demonstrated.

The effect of both thermal annealing and plasticization of the polymeric matrix by low molecular weight compounds on the electrical conductivity of the polystyrene based carbon nanotubes (CNTs) composites were investigated. It was found that the electrical conductivity of the samples filled with 3 wt% of CNTs increased by nearly 2 orders of magnitude after thermal annealing for 10 h at 150 °C, and it further increased with increasing plasticizer content. The effect of the hierarchical CNT morphology on the electrical conductivity of composites was elucidated by in-situ Raman and Synchrotron Radiation Small Angle X-ray Scattering investigations. The synergistic effect between thermal treatment and matrix plasticization contributes to efficiently eliminate the residual stress at the interface between polymeric matrix and carbon nanotubes. This leads to the formation of a more effective CNTs network featured by more dense bundles, exhibiting a larger number of contacts between the CNTs which contributes to significantly enhance the electrical conductivity of composites.

A mechanically controlled atom transfer radical polymerization (mechanoATRP) was successfully carried out in an ultrasound bath with low ppm of copper catalyst. The polymerization of methyl acrylate in the presence of CuBr2/tris(2-pyridylmethyl)amine catalyst using ultrasound as an external stimulus was temporally controlled by switching on–off ultrasound agitation. The first order kinetics was observed during ultrasonication. The experimental molecular weights agreed well with the theoretical values and displayed narrow molecular weight distribution. The effects of various types of piezoelectric BaTiO3 nanoparticles, loadings of nanoparticles, and targeted degrees of polymerization were studied.

A facile one-step electrospraying technology was utilized to produce a novel kind of hollow polyurethane (PU) microspheres with controlled size and tunable surface morphology by adjusting the experiment parameters such as solvent, flow rate, applied voltage, and solution concentration. A porous-hollow structure can be obtained by increasing flow rate or solution concentration, or decreasing applied voltage. The decrease of flow rate or solution concentration, or the increase of applied voltage leads to hollow structures with a non-porous surface. The formation of porous-hollow morphology involves the PU polymer chains deposition during the solvent evaporation process and a phase separation phenomenon induced by the anti-solvent behavior in the water bath. The results demonstrate that the electrospraying method is a novel and facile method for preparing hollow polymer microspheres with tunable surface structures, and the obtained PU microspheres offer diversified applications ranging from adsorbents to drug delivery systems.

Inspired by the jellyfish breathing, we developed a novel strategy to construct an ultrasound-responsive fluorescent polymer assemblies. Upon exposed to ultrasound, the assemblies underwent a significant drop in fluorescence intensity (>80%), solution transmittance and particle size. Re-addition of zinc salt can restore the fluorescence and size of the assemblies.

Platinum-decorated graphene aerogel microspheres were fabricated through a combined electrospraying, freeze-casting, and solvothermal process. Platinum nanoparticles with a narrow size distribution are evenly anchored on the graphene aerogel microspheres without agglomeration benefitting from the distinct center-diverging microchannel structure of the graphene aerogel microspheres, which results in the as-prepared catalysts presenting excellent electrocatalytic performance including high electrocatalytic activity and high poison tolerance toward methanol electro-oxidation, showing great potential for direct methanol fuel cell anode catalysts. In particular, the platinum-decorated graphene aerogel microspheres exhibit an extremely high mass activity of 1098.9 mA mg–1 toward methanol oxidation as well as excellent antipoisoning ability, which are dramatically enhanced compared with Pt particles dispersed on graphene oxide and commercial carbon black supports.

Mesoporous silica nanoparticles (MSN) covered by polymer coatings, cross-linked by weak coordination bonds were expected to present a reversible responsiveness under on-off ultrasound stimuli. Herein, we prepared a sodium alginate (SA) modified MSN with carboxyl-calcium (COO−-Ca2+) coordination bonds in the modified layer, which could block the mesopores of MSN and effectively prevent the cargo from pre-releasing before stimulation. The coordination bonds would be destroyed under the stimulation of low intensity ultrasound (20 kHz) or high intensity focused ultrasound (HIFU, 1.1 MHz), leading to a rapid and significant cargo release, and then they could be reformed when ultrasound was turned off, resulting in an instant cargo release stopping. The reversible cleavage and reformation of this coordination bonds under on-off ultrasound stimulus were confirmed by the gel-sol transition behaviors of the SA-CaCl2 gels. An excellent real-time control of rhodamine B (RhB) release performance was obtained under the ultrasound stimuli. Obviously, the cargo release ratio could reach to nearly 40% when HIFU (80 W) was turned on for 5 min, and remained basically constant when ultrasound was turned off, which would finally reach to nearly 100% within 30 min under this on-off pulsatile status. These hybrid MSN based nanoparticles with excellent reversible ultrasound on-off responsiveness were of great interest in on-demand drug delivery applications in the future.

Electrically conductive and flexible thermoplastic polyurethane/graphene (TPU/GE) porous structures were successfully fabricated by selective laser sintering (SLS) technique starting from graphene (GE)-wrapped thermoplastic polyurethane (TPU) powders. Several 3D mathematically defined architectures, with porosities from 20% to 80%, were designed by using triply periodic minimal surfaces (TMPS) equations corresponding to Schwarz (S), Diamond (D), and Gyroid (G) unit cells. The resulting three-dimensional porous structures exhibit an effective conductive network due to the segregation of graphene nanoplatelets previously assembled onto the TPU powder surface. GE nanoplatelets improve the thermal stability of the TPU matrix, also increasing its glass transition temperature. Moreover, the porous structures realized by S geometry display higher elastic modulus values in comparison to D and G-based structures. Upon cyclic compression tests, all porous structures exhibit a robust negative piezoresistive behavior, regardless of their porosity and geometry, with outstanding strain sensitivity. Gauge factor (GF) values of 12.4 at 8% strain are achieved for S structures at 40 and 60% porosity, and GF values up to 60 are obtained for deformation extents lower than 5%. Thermal conductivity of the TPU/GE structures significantly decreases with increasing porosity, while the effect of the structure architecture is less relevant. The TPU/GE porous structures herein reported hold great potential as flexible, highly sensitive, and stable strain sensors in wearable or implantable devices, as well as dielectric elastomer actuators.

We present the polarization-dependent highly absorptive in Ka-band composition of conventional polyurethane foam filled with in situ synthesized aerogel coated by reduced graphene oxide (rGO). The rGO-based aerogel was in situ prepared into the open-cell polyurethane foam (PUF) skeleton through a bidirectional freeze-drying process. The aerogel is composed of the flat lamellas stacks, possessing the anisotropic structure and unique electromagnetic properties. Further improvement of the electromagnetic shielding ability was possible by the rGO coating introduction as a coupling layer between PUF and rGO-based aerogel. This enhances the overall conductivity of the resulting composites: 1.41 + 3.33i S/m vs. 0.9 + 2.45i S/m for PUF loaded with in situ synthesized aerogel without rGO coating.With this mechanically robust plane easy to process coating one could achieve &minus, 20 dB by power with the record light structure (0.0462 g/cm2). That could compete in view of the weight per cm2 even with graphene-based absorbers comprising either dielectric matching elements or back metal reflectors, or both.

Adsorption is used extensively to deal with increasingly serious water pollution. In this paper, beta-cyclodextrin-graphene oxide aerogel microspheres (CD-GAM) with 3D porous structure was prepared by electrospraying combining with freeze-casting and sequently mild self-assembly. Owing to the integration of graphene oxide (GO) and beta-cyclodextrin (β-CD), the CD-GAMs exhibit excellent broad-spectrum adsorption capabilities for dyes and organic micropollutants, including anionic dyes of methylene blue (439 mg/g) and Rhodamine B (388 mg/g), cationic dyes of acid red 87 (234 mg/g) and methyl orange (167 mg/g), organic micropollutants aromatic model compound of carcinogen 2,4-dichlorophenol (17 mg/g), pharmaceuticals of propranolol hydrochloride (49 mg/g), contraceptive ethynyl estradiol (19 mg/g) and plastic components bisphenol A (38 mg/g). The adsorption capacity of CD-GAM for most pollutants reach equilibrium within 10 min. In addition, the CD-GAM maintained stable regenerative adsorption capacity more than 80 % in five cycles. The broad-spectrum adsorbent CD-GAM is an ideal choice for removing complex and diverse pollutants from wastewater.

Elastomeric conductive composites (ECCs) based on carbonaceous fillers are very attractive and play a significant role in the field of smart sensors due to their excellent flexibility, high and wide-spectrum sensitivity as well as fast response to external stimuli. In this study, a lightweight and multi-sensing composite based on reduced graphene oxide/natural rubber (rGO/NR), is fabricated by a facile and cost-effective approach that combines the rGO assembling on rubber latex particles by graphene oxide in-situ reduction and mild drying of the resulting hydrogels. The resulting composites exhibit a reliable porous structure whereas the rGO is spatially distributed in a three-dimensional segregated morphology that percolates the samples. The composites are characterized by a low percolation threshold (

The reinforcing and synergistic effect of a 1D filler (cellulose nanocrystals) and of a 2D filler (reduced graphene oxide) in a high amorphous vinyl alcohol (HAVOH) polymer has been investigated. Nanocomposite films have been obtained by dissolving in water the HAVOH polymer and suitable fillers, thus leading to the formation of a very promising material for eco-friendly food packaging applications. In addition, the effect of (3-Mercaptopropyl) trimethoxysilane as crosslinking agents for the vinylalchol-based polymer has been studied. FTIR and XPS results clearly show that the presence of mercapto silane has a twofold effect. Mercapto groups have the capability to reduce chemically the graphene oxide (GO) filler to reduced graphene oxide (rGO) during the preparation of the HAVOH-based composites and to crosslink the HAVOH structure. Tensile tests show that the effect of siloxane crosslinking leads to an embrittlement of the HAVOH matrix, which is avoided when rGO e cellulose nanocrystals (CNC) are dispersed in the composites. The permeability results show that all the composites exhibit better barrier properties than pristine HAVOH. Particularly, the highest water permeability reduction of about 45% is observed for the sample containing 1% wt/wt GO and 1% wt/wt CNC. This significant drop in permeability is likely related to three concurrent effects, a) the crosslinking of HAVOH matrix, b) the binding of water molecules due to CNC presence and c) the more hydrophobic behaviour associated to a high amount of rGO.

Superhydrophobic and crosslinked poly(vinyl alcohol) (PVA)/cellulose nanofibril (CNF) aerogel microspheres were prepared via a combination of the water-in-oil (W/O) emulsification process with the freeze-drying process, followed by thermal chemical vapor deposition of methyltrichlorosilane. The oil phase and the cooling agent were judiciously selected to ensure that the frozen ice microspheres can be easily separated from the emulsion system. The silanized microspheres were highly porous with a bulk density ranging from 4.66 to 16.54mg/cm(3). The effects of the solution pH, stirring rate, and emulsifier concentration on the morphology and microstructure of the aerogel microspheres were studied. The highly porous structure of the ultralight aerogel microspheres demonstrated an ultrahigh crude oil absorption capacity (up to 116 times its own weight). This study provides a novel approach for the large-scale preparation of polymeric aerogel microspheres with well-controlled particle sizes that can be used for various applications including oil and chemical spill/leak clean-up.