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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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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...

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 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.

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.

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.

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.

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.

The reduced graphene oxide (rGO) modified natural rubber composite (NR) filled with high contents of silica was prepared by a wet compounding and latex mixing process using a novel interface modifier cystamine dihydrochloride (CDHC) with coagulation ability. CDHC acts as a coagulation agent through electrostatic interaction with rGO, SiO2, and latex rubber particles during the latex-based preparation process, while in the obtained silica/graphene/natural rubber composites, CDHC acts as an interface modifier. Compared with the composites prepared by the conventional mechanical mixing method, the dispersion of both rGO and SiO2 in the composites made by a wet compounding and latex mixing process is improved. As a result, the obtained silica/graphene/natural rubber composite prepared by this new method has good comprehensive properties. A Dynamic Mechanical Test suggests that the tan &delta, values of the composites at 60 oC decrease, indicating a low rolling resistance with increasing the graphene content at a low strain, but it increases at a higher strain. This unique feature for this material provides an advantage in the rubber tire application.

Elastomer-based porous structures realized by selective laser sintering (SLS) are emerging as a new class of attractive multifunctional materials. Herein, a thermoplastic polyurethane (TPU) powder for SLS was modified by 1 wt.% multi-walled carbon nanotube (MWCNTs) or a mixture of MWCNTs and graphene (GE) nanoparticles (70/30 wt/wt) in order to investigate on both the synergistic effect provided by the two conductive nanostructured carbonaceous fillers and the correlation between formulation, morphology, and final properties of SLS printed porous structures. In detail, porous structures with a porosity ranging from 20% to 60% were designed using Diamond (D) and Gyroid (G) unit cells. Results showed that the carbonaceous fillers improve the thermal stability of the elastomeric matrix. Furthermore, the TPU/1 wt.% MWCNTs-GE-based porous structures exhibit excellent electrical conductivity and mechanical strength. In particular, all porous structures exhibit a robust negative piezoresistive behavior, as demonstrated from the gauge factor (GF) values that reach values of about &minus, 13 at 8% strain. Furthermore, the G20 porous structures (20% of porosity) exhibit microwave absorption coefficients ranging from 0.70 to 0.91 in the 12&ndash, 18 GHz region and close to 1 at THz frequencies (300 GHz&ndash, 1 THz). Results show that the simultaneous presence of MWCNTs and GE brings a significant enhancement of specific functional properties of the porous structures, which are proposed as potential actuators with relevant electro-magnetic interference (EMI) shielding properties.

Selective laser sintering (SLS) is one of the mainstream 3D printing technologies. A major challenge for SLS technology is the lack of novel polymer powder materials with improved Z-direction strength. Herein, a dynamic polymer was utilized to solve the challenge of SLS. To verify this concept, novel cross-linked poly(chlorophenol-urethane) (PCP-PU) and poly(bromophenol-urethane) (PBP-PU) containing dynamic halogenated bisphenol carbamate bond were examined. The obtained dynamic polyurethane exhibited excellent mechanical strength and self-healing efficiency, in addition to SLS processing ability. A small molecule model study confirmed the dynamic reversible characteristics of the chlorinated bisphenol carbamate, which dissociates into isocyanate and hydroxyl at 120 °C and reforms at 80 °C, as confirmed by NMR and FT-IR. SLS 3D printing using the self-made healable PBP-PU powders was successfully realized. The interface interaction between the adjacent SLS layers can be significantly improved via dynamic chemical bond linking instead of traditional physical entanglement, which leads to an improved Z-direction mechanical strength. The SLS processed PBP-PU sample exhibits an X-axis tensile strengths of ∼23 MPa and an elongation at break of ∼600 %. The Z-axis tensile strength is ∼88 % of X-axis’s, much higher than that of control TPU sample (∼56 %).

Combining self‐healing functions with damage diagnosing, which can achieve timely healing autonomously, is expected to improve the reliability and reduce life cycle cost of materials. Here, a flexible conductive composite composed of a dynamically crosslinked polyurethane bearing Diels–Alder bonds (PUDA) and carbon nanotubes (CNTs), which possess both crack diagnosing and self‐healing functions, is reported. The introduced dynamic Diels–Alder bonds endow the materials self‐healing function and the powder‐based preparation route based on the specially designed CNTs‐coated PUDA micropowders leads to the formation of segregated CNTs network, which makes the composite possess excellent mechanical properties and high conductivity. Because of the sufficient electrothermal and photothermal effect of CNTs, the composites can be healed rapidly and repeatedly by electricity or near‐infrared light based on the retro‐Diels–Alder reaction. An obvious color difference in the infrared thermograph resulting from the resistance difference between damaged and undamaged area can be observed when applying the voltage, which can be used for crack diagnosing. Using the same electrical circuit, the crack in the PUDA/CNTs composite can be noninvasively detected first and then be autonomously healed. The composites also exhibit a strain‐sensing function with good sensitivity and high reliability, thus will have potential applications in electronic strain sensors.

The extensively used latex mixing approach to prepare graphene can improve the graphene dispersion but meets some challenges in the preparation of high content carbon black filled rubber system like a rubber tire. Owing to the high melt viscosity of the rubber/graphene masterbatch, the dispersion of carbon black is not perfect during twin-roll mixing and some aggregates will be formed. Here we proposed a wet compounding process, combined with ultrasonically assisted latex mixing, named as the WCL method to prepare reduced graphene oxide/carbon black/natural rubber (rGO/CB/NR) composites. The morphological observations confirmed that both graphene and carbon black can be evenly dispersed in the rubber composites. The incorporation of rGO also improves the hardness, thermal conductivity and anti-aging properties of the composites. The rGO/CB/NR composites prepared by the WCL method possess better mechanical properties compared to conventional latex mixing. The entanglement-bound rubber tube model was utilised to understand the reinforcing mechanism.

The in-situ bulk polycondensation process in combination with a ball milling dispersion process was used to prepare the water blown multiwall carbon nanotubes (CNT)/polyurethane (PU) composite foam. The mechanical properties, piezoresistive properties, strain sensitivity, stress and resistance relaxation behaviors of the composite foams were investigated. The results show that the CNT/PU composite foam has a better compression strength than the unfilled polyurethane foams and a negative pressure coefficient behavior under uniaxial compression. The resistance response of CNT/PU nanocomposites foam under cyclic compressive loading was quite stable. The nanocomposite foam containing a weight fraction of carbon nanotubes close to the percolation threshold presents the largest strain sensitivity for the resistance. The characteristic of resistance relaxation of CNT/PU composite foam is different from the stress relaxation due to the different relaxation mechanism. During compressive stress relaxation, the CNT/PU foam composites have excellent resistance recoverability while poor stress recoverability.

Composite materials with 2D carbon (graphene and/or single wall carbon nanotubes) are very promising due to their extraordinary electrical and mechanical properties. Graphene and natural rubber composites, which may be used for the gaskets or sealants, were prepared by ultrasonically assisted latex-mixing exfoliation and in-situ reduction process, with two vulcanization approaches: roll-mixing and hot-pressing. Also the resin-based composites, filled with micro-particles of Ag and graphene or carbon nanotubes, have been studied. The standards for the compositional characterization of these materials still are not established. In addition to the mostly used techniques, such as Raman spectroscopy and electron microscopy, also Auger electron spectroscopy can be employed for the identification of graphene. In this study, the shape of C KVV peak, excited by electron beam and X-ray photons, has been investigated in different composite materials containing graphene and carbon nanotubes. A spectroscopic method for 2D carbon recognition, based on the D x parameter which is determined from C KVV signal excited by X-ray photons, was proposed and verified. Even a small content of graphene in different types of composites was sufficient for this recognition due to the dominating presence of graphene on the surface of composites.

Superhydrophobic poly(vinyl alcohol) (PVA)/cellulose nanofibril (CNF) aerogels with a unidirectionally aligned microtubular porous structure were prepared using a unidirectional freeze-drying process, followed by the thermal chemical vapor deposition of methyltrichlorosilane. The silanized aerogels were characterized using various techniques including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and contact angle measurements. The structure of the aerogels fully filled with polydimethylsiloxane (PDMS) was confirmed by SEM and optical microscopy. The mechanical properties of the resulting PDMS/aerogel composites were examined using both compressive and tensile tests. The compressive and tensile Young's moduli of the fully filled PDMS/aerogel composites were more than 2-fold and 15-fold higher than those of pure PDMS. This study provides a novel alternative approach for preparing high performance polymer nanocomposites with a bicontinuous structure.

Natural rubber containing graphene and carbon nanotubes (CNTs) composites were prepared by ultrasonically- assisted latex mixing. Natural rubber filled by both graphene and CNTs show significant enhanced tensile strength, while graphene exhibits a better reinforcing effect than CNTs. Strain-induced crystallization in natural rubber composites during stretching was determined by synchrotron wide-angle X-ray diffraction. With the addition of CNTs or graphene, the crys- tallization for natural rubber occurs at a lower strain compared to unfilled natural rubber, and the strain amplification effects were observed. The incorporation of graphene results in a faster strain-induced crystallization rate and a higher crystallinity compared to CNTs. The entanglement-bound rubber tube model was used to analyze the chain network structure and deter- mine the network parameters of composites. The results show that the addition of graphene or CNTs has an influence on the molecular network structure and improves the contribution of entanglement to the conformational constraint, while graphene has a more marked effect than CNTs.

High-intensity focused ultrasound (HIFU) was developed as a spatial selective annealing method to control the crystallization behavior and performance of polymer using amorphous polyethylene terephthalate (PET) as an example for demonstration. The spatial crystallization and morphological details of HIFU induced crystallization areas at the lamellar level and spherulite scale were studied by Micro-Focus hard X-ray diffraction, small angle X-ray scattering and optical microscopy. According to the distribution of crystallinity of PET, we can indirectly detect the history of thermal distribution of the ultrasonic focal point, which is hard to obtain by other methods. The crystallinity and the area of the crystalline region of PET sample increased with ultrasound power or irradiation time. Different from common crystalline structure of polymer materials, HIFU induced crystallinity of PET has a significant gradient distribution. The gradient crystal structure leads to a better mechanical performances, which can realize the good balance between toughness and strength. Ultrasound annealing, as a complement and development of the traditional annealing technology, has the characteristics of high efficient and spatial selectivity, showing great application prospect in post processing field.

The spatial distribution of graphene oxide (GO) nanoplatelets in a bromobutyl rubber (BBR) matrix has been tailored by exploiting the rubber latex mixing process to confine nanoparticles among latex microspheres, thus obtaining a segregated arrangement. The gas transport properties and the dielectric behavior of these nanocomposites displaying a 'segregated' morphology have been compared, for different filler contents, to those of BBR/GO nanocomposites in which the nanoparticles are uniformly dispersed within the rubber matrix. Relevant qualitative and quantitative differences emerge from the comparison of the properties of the two families of GO-based samples. It has been found that the segregated morphology enables a significant enhancement of the barrier properties of pristine rubber already at low levels of nanofiller loading. In addition, an exceptionally low value of the electrical percolation threshold has been detected, which is more than one order of magnitude lower than in the case of uniform filler dispersion. These effects are a direct consequence of the assembly and confinement of nanoparticles among the rubber latex microspheres. (C) 2016 Elsevier Ltd. All rights reserved.

A unique property of photothermal effect-based shape-memory polymers (SMPs) is demonstrated using a chemically cross-linked poly(ethylene oxide) (PEO) loaded with a small amount (0.5 wt %) of gold nanoparticles (AuNPs). We show that controlled surface plasmon resonance absorption of AuNPs allows for the formation of a temperature gradient in the polymer of temporary shape, which results in anisotropic polymer chain relaxation and strain energy release. This photoinduced temperature gradient effect enables the use of a laser to create a multitude of deformations and to control sophisticated motion executing mechanical work that are otherwise inaccessible with SMPs.

The concept of using ultrasound to trigger shape memory assisted healing of covalently cross-linked dynamic polymers is demonstrated. The well-designed dynamically crosslinked poly(e-caprolactone)-based polyurethane bearing Diels–Alder bonds not only possesses high mechanical strength and toughness, but also exhibits shape memory assisted crack-closure and healing upon exposure to high-intensity focused ultrasound owing to breaking and reformation of dynamic bonds. The use of focused ultrasound allows the healing process to be activated remotely and to be controlled locally by depositing the acoustic energy only in the damaged region without detriment to the undamaged parts of the material. The healable polyurethane materials have potential applications such as long-term load-bearing engineering components and anti-fatigue medical devices.

A general method for preparing mechanically strong hydrogels that can undergo light-triggered healing was demonstrated. By loading a small amount of gold nanoparticles (AuNPs, 0.05 wt%) in hydrogels prepared with stearyl acrylate (SA), N,N-dimethylacrylamide (DMA) and N,N′-methylenebisacrylamide (MBA), whose strength is endowed by chemical crosslinking coexisting with crystallized hydrophobic SA side chains acting as the physical crosslinks, exposing a cut-through damage to a laser of wavelength at the surface plasmon resonance of AuNPs and subsequently turning off the light, gives rise to efficient healing of the hydrogel as a result of the reversible melting–crystallization phase transition of the hydrophobically associated SA chains. A hydrogel of this kind exhibits an unprecedented tensile strength, after repairing, of greater than 2 MPa. It also displays a light-controllable shape memory effect.

High intensity focused ultrasound (HIFU)-triggered shape memory has distinct features due to the unique heating mechanism based on polymer chain shearing and friction activated by ultrasonic energy. In this study we chose crosslinked poly(methyl methacrylate-co-butyl acrylate) P(MMA-BA) as a model polymer and studied in detail the HIFU induced thermal effect and shape recovery characteristics. It was found that HIFU heating for polymers is quick and spatially localized, and can be controlled by the ultrasound power, which allows for a spatiotemporally controllable shape memory process. The effects of various parameters including sample thickness, copolymer composition and crosslinker content on the HIFU-induced thermal effect and shape recovery were investigated. Under HIFU irradiation, there exists an optimum sample thickness for a maximum thermal effect and thus better shape recovery, which is different from conventional heating. Moreover, both the copolymer composition and the crosslinker content have a profound effect on the HIFU-induced temperature rise and thus the shape recovery. These effects can be related to changes in the viscoelastic parameter loss tangent (tan δ) of the copolymer around the glass transition temperature Tg that is the transition temperature for the shape recovery process.

Silicone rubber membrane with ordered micropores in the surface was prepared by means of the solvent evaporation-induced phase separation. A ternary solution including liquid silicone rubber precursor, liquid paraffin, and hexane was cast to form a film with a two-phase structure after the hexane was evaporated. The micropores were generated by removing liquid paraffin phase in the cured silicone rubber film. The effects of the liquid paraffin concentration, casting temperature, initial casting solution thickness, air circulation, and addition of surfactant Span-80 on the pore structure in the membrane surface were investigated. The average pore size increases with increasing liquid paraffin concentration or the initial casting solution thickness. The formation of pore structure in the membrane surface is related to the phase separation and thus the phase separation process of the casting solution surface was in situ observed using the digital microscope. The formation mechanism of pore is attributed to a nucleation, growth, and coalescence process of liquid paraffin phase in the membrane surface.

In this paper the synergistic effects of both 3-amminopropryltriethoxy silane (APTES) functionalization and silica enrichment of carbon nanotubes on thermal and thermal-mechanical properties of epoxy based composite materials were investigated. Pristine multiwalled carbon nanotubes were oxidized, functionalized with APTES and then modified with silica nanoparticles preformed through the Stober process. The FTIR, XPS and TGA analysis confirmed the occurrence of the silane functionalization and surface silica enrichment. TEM analysis showed the presence of a “bunches” morphology where silica nanoparticles aggregated around both the CNTs wall and their ends. Thermo-mechanical, thermal and flammability properties of nanocomposite containing 1 wt% of different fillers were determined and results compared to neat epoxy resin. Results showed that both the elastic and rubbery modulus increase with the addition of filler. In particular, in the rubbery region, the storage modulus of composites with silanized and silica enriched carbon nanotubes were about 240% and 285% higher than modulus of neat epoxy system. In the glassy region, a modest increment of 25% for the storage modulus was recorded. The glass transition temperature increased of about 20 °C with silica enriched carbon nanotubes alongside with a significant enhancement of the damping behavior.

Natural rubber (NR) containing graphene (GE) and graphene oxide (GO) were prepared by latex mixing. The in situ chemically reduction process in the latex was used to realize the conversion of GO to GE. A noticeable enhancement in tensile strength was achieved for both GO and GE filled NR systems, but GE has a better reinforcing effect than GO. The strain-induced crystallization was evaluated by synchrotron wide-angle X-ray diffraction. Increased crystallinity and special strain amplification effects were observed with the addition of GE. The incorporation of GE produces a faster strain-induced crystallization rate and a higher crystallinity compared to GO. The entanglement-bound tube model was used to characterize the chain network structure of composites. It was found that the contribution of entanglement to the conformational constraint increases and the network molecular parameters changes with the addition of GE and GO, while GE has a more evident effect than GO. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Bis-(triethoxysilylpropyl)-tetrasulfane functionalised carbon nanotubes (t-CNTs) were used as compatibiliser along with liquid isoprene rubber (LIR) in the natural rubber (NR)/polybutadiene rubber (BR) blend. Their reinforcing and compatibilising effects were evaluated by mechanical, fatigue crack growth resistance properties and blend homogeneity. Scanning electron microscope and transmission electron microscope showed enhanced interfacial adhesion between the binary rubber phases and improved dispersion of the minor phase in the rubber blend respectively with the co-existence of LIR and carbon nanotubes. The tensile strength of the carbon black (CB) filled NR/BR blend reached its optimum when 3 phr CB was replaced with an equal amount of t-CNTs in the presence of 7 phr LIR, while the fatigue crack growth resistance property achieved its maximum in the presence of 3 phr LIR. This interesting co-compatibilisation behaviour of t-CNTs and LIR suggests that t-CNTs have a better effect than CB with the assist...

Self-assembling of reduced graphene oxide (RGO) and graphene oxide (GO) platelets, as a tailored interconnected network within natural rubber and butyl rubber matrices, is proposed as a mean for obtaining nanocomposites with significantly enhanced functional properties as compared to unloaded rubber, i.e. gas barrier properties and electric conductivity, even at very low filler contents. Interestingly, the prescribed spatial arrangement of the nanoparticles ('segregated arrangement') results to be much more effective in improving properties than homogeneous dispersion ('not segregated' arrangement) of platelets, even at low loadings. The 'segregated' structure originates from the confinement of platelets within the interstices of the coagulated latex particles, which act as a template for the network formation. The platelets are assembled on the latex particles giving rise to spheres with a core-shell structure, with a partial or complete covering depending on graphene amount. Conversely, the 'not-segregated' structure is obtained by destroying this interconnected network by further processing the nanocomposite masterbatch via twin-roll mixing, thus determining a uniform orientation of exfoliated platelets.

It is discovered that poly(vinyl alcohol) (PVA) hydrogel prepared using the freezing/thawing method can self-repair at room temperature without the need for any stimulus or healing agent. The autonomous self-healing process can be fast for mechanically strong PVA hydrogel yielding a high fracture stress. Investigation on the effect of the hydrogel preparation conditions points out that hydrogen bonding between PVA chains across the interface of the cut surfaces is at the origin of the phenomenon. The key for an effective self-healing is to have an appropriate balance between high concentration of free hydroxyl groups on PVA chains on the cut surfaces prior to contact and sufficient PVA chain mobility in the hydrogel.