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In the quest for sustainable and renewable energy sources, researchers and engineers have explored innovative technologies to harvest energy from various environmental sources. Dielectric elastomer generators (DEGs) with high energy harvesting performance have been proven to be promising energy collectors, but achieving a high dielectric constant (ε’) and low electrical conductivity (EC) under high electric fields of dielectric elastomer (DE) simultaneously is a struggle, which poses significant challenges. In this study, high-content carboxyl group-grafted liquid polybutadiene (HCPB) is synthesized and then adopted as an organic dielectric filler to blend and cocross-link with a butadiene rubber (BR) matrix to prepare DE composites with high energy harvesting performance. The introduction of carboxyl groups enhances polarization while trapping free Al3+in the matrix, which revolutionarily achieves a significant increase in ε’ under extremely low EC. Ultimately, the contradiction between increased ε’ and decreased ECunder high electric fields is reconciled, resulting in a 30 HCPB/BR composite with high energy density (w= 91.9 mJ/cm3) and fine power conversion efficiency (PCE= 24.1%). This advancement paves the way for the development of HCPB/BR composite-based DEGs with enhanced ε’ and energy harvesting performance.

In this study, a hydrogenated nitrile rubber (HNBR)/tetrafluoroethylene, ethylene, and hexafluoropropylene terpolymer (EFEP) thermoplastic vulcanizate (TPV) is prepared by decreasing the cohesive energy density of HNBR, improving the compatibilization of two phases via dioctyl phthalate, and optimizing the cross-linking characteristics and the dynamic vulcanization process. The as-produced HNBR/EFEP TPV exhibits a fine dispersion of the HNBR phase within the EFEP matrix, resulting in good mechanical and rheological properties, high elasticity, excellent recyclability, high resistance to heat and oil, and good gas barrier properties. The morphological evolution of the HNBR/EFEP TPV indicates that the development of the microstructure is controlled by the in situ cross-linking and clustering of HNBR particles, with the subsequent breakup of the rubber particle aggregates. The enhancement of the compatibility of HNBR/EFEP and the effect of the shearing force led to a reduction in the size of HNBR particle agglomerates and an enhancement in the quantity of single HNBR particles during dynamic vulcanization.

•Some representative design ideas and methods for preparing DEA driven soft robots are described.•The configuration and performance requirements of DEA for various bioinspired robots are introduced.•Perspectives of research on developing new DEA materials and improving DEA performances are proposed.

As the most promising soft actuator, dielectric elastomer actuator (DEA) possesses high actuated strain and fast response, and thus it finds applications in artificial muscle and soft robot etc. However, the low output force of DEA limits its potential application. The multi-layer stacked DEA is regarded as an effective approach to enhance the output force. Nevertheless, multi-layer stacked DEA fabricated by wet stacking suffers from non-uniformity between layers, while dry stacking suffers from weak interfacial adhesion between layers. Herein, a method for preparation of multi-layer stacked DEA by co-crosslinking of conductive rubber electrode with DE substrate was developed. Titanium dioxide (TiO2)/Polymethylvinylsiloxane (PMVS) composites with simultaneously high dielectric constant, low modulus, high breakdown strength and low dielectric loss were prepared and used as DE substrate, while superconducting carbon black (CB)/Polydimethylsiloxane (PDMS) composites were prepared and used as the vulcanized rubber electrode. By co-crosslinking of electrode with DE substrate, the resultant multi-layer DEA exhibits not only strong adhesion between layers, but also a good stability, combining the advantages of dry stacking and wet stacking. Meanwhile, TiO2/PMVS composite DEA presents a large actuated strain of 50.3% and a high output force of 0.31 N. By stacking three layers of TiO2/PMVS films with electrode, the three-layer stacked DEA can obtain a high output force of 0.88 N and high energy output of 7.14 mJ, 2.84 times and 1.5 times of single layer DEA, respectively. This method provides a new idea for developing multi-layer stacked DEA with higher energy output and output force of DEA.

Thermoplastic vulcanizates (TPVs) are among the most concerned polymer materials because they exhibit a combination of good elasticity and easy processibility and recyclability. Herein, a β-nucleating agent (β-NA) was introduced into ethylene propylene diene monomer (EPDM)/polypropylene (PP) TPVs through a simple and effective postprocessing method to induce the formation of β-PP crystals for preparing high-performance TPV products. High content of β-PP crystals is achieved in TPV, but the total crystallinity of the PP matrix remains constant. Unexpectedly, both mechanical strength and elasticity of TPV with β-PP crystals (β-TPV) are significantly higher than those of TPV with α-PP crystals (α-TPV). The change in the structure of both α-TPV and β-TPV during real-time deformation and the deformation mechanism was carefully studied by combining Synchrotron two-dimensional wide-angle X-ray diffraction (2D-WAXD) and atomic force microscopy nanomechanical mapping (AFM-NM) techniques. The mechanism for the simultaneous improvement of mechanical strength and elasticity of TPV is revealed.

The shape memory thermoplastic polyurethane (TPU) generally exhibits a phase-separated structure, in which the hard segments form the hard domains via hydrogen bonds, and plays an important role in shape recovery. However, the physical interaction in the hard domains is always weak, resulting in a permanent deformation and thus decreasing the shape-recovery ability of TPU significantly. In this research, a new type of diol chain extender containing anthracene groups was synthesized, and the photoresponsive anthracene groups were incorporated into the hard segment of TPU. The stability in hard domains and recoverability could be tailored by different UV irradiation times via the photodimerization of anthracene groups, and the shape-recovery ratio and the shape-fixing ratio were still both above 93%, even when the strain reached 270%. More importantly, the shape-free reconfiguration is achieved through the dimerization of anthracene groups under UV irradiation, which achieved free construction of three-dimensional (3D) shapes without templates. Thus, the spontaneous shape change from two-dimensional (2D) to 3D was realized, in combination with melting transition, and the dedimerization of anthracene ensured the recyclability of polyurethane at T= 150 °C. This simple and facile strategy could be used to fabricate the recyclable and photoplasticity shape memory TPU with a high shape-fixing/recovery ratio at large deformation, and it would have a wider range of potential application in stents.

Mapping and phase identification of the structure and mechanical property evolution of self-reinforced rubbers during deformation are difficult but important to reveal the self-reinforcement mechanism and fabricate advanced rubber products. Here, using the atomic force microscopy (AFM) nanomechanical mapping technique, and combined with Gaussian fitting of the modulus distribution profiles and recolored AFM modulus-mapping images, the structural evolution and mechanical response of deformed isoprene rubber (IR) has been identified quantitatively and visually. The results indicated that the entire rubber molecular segments were oriented during stretching, and the orientation was not uniform. The highly oriented shish-kebab structure along the stretching direction was directly observed in the crystalline-associated phase, which was responsible for the significant self-reinforcement. In addition, the crystallinity estimated by AFM observation was similar to the wide-angle X-ray diffraction (WAXD) results. Based on the AFM and WAXD results, a schematic model was proposed to illustrate the structural evolution and self-reinforcement mechanism of IR.

Medical fixing is one of the very important applications of the shape-memory polymer material, and the two important properties of the medical fixing material are that it perfectly fits the body during the fixing and easily detaches after being used. As the fixing and detachment are triggered by two independent stimuli in two opposite directions, it is necessary to develop multidirectional triple-shape-memory polymers. In this research, a series of polymer materials composed of trans-polyisoprene (TPI) and paraffin were prepared by melt blending and compression molding, and then the TPI was cross-linked by vulcanization. As a result of the large difference in the melting temperature and crystallization temperature between TPI and paraffin, the obtained polymer materials exhibit a triple-shape-memory behavior. According to the analysis of crystal behavior, microscopic morphology, and mechanical properties of the materials with different paraffin contents and TPI cross-linking density by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and dynamic mechanical thermal analysis, the shape-memory behavior of the obtained materials was tunable by the cross-linking density of TPI and the crystallization degree of TPI or paraffin. Compared with the traditional triple-shape-memory material, our samples are prepared in a more facile way and can recover at human body temperature (37 °C). Moreover, our TPI/paraffin material can realize more flexible multidirectional recovery, as well as can be reprogramed and used multiple times. To the best of our knowledge, there are few polymer materials reported, which can realize multidirectional recovery. These unique multidirectional and reprogramable properties will enable the application of this polymer material, especially in the medical fixing materials.

Based on the adhesive mechanism of mussels, we present a facile strategy to prepare nanocomposite polydopamine–poly(N-acryloyl glycinamide)–graphene oxide (PDA–PNAGA–GO) hydrogels with lots of catechol groups in the matrix of hydrogel. The microfibril structure formed by PDA chains enables the hydrogels high stretchability (∼1500%) and toughness (6990 J/m2); the multiple hydrogen bonding interactions and π–π interactions among the PNAGA network and PDA chains also enable a hydrogel perfect self-healing performance. Moreover, GO in the hydrogel can absorb the near-infrared irradiation, resulting in the temperature difference between the surface and bottom area and then a bending deformation (with 40% of actuation degree) of the hydrogel. Besides, the GO can also make the hydrogels electrically conductive, and the self-healing efficiency (∼87% for the first healing) could also be calculated according to the retention rate of conductivity of hydrogel after being healed at 90 °C. The unique properties will enable the PDA–PNAGA–GO hydrogels to be widely used in the field of tissue engineering and soft actuators.

A highly stretchable conductor was fabricated through dip-coating a new liquid metal (LM) electric ink on a polydopamine (PDA)-modified three-dimensional (3D) polyurethane sponge (PUS) followed by mechanical sintering. The LM was first sonicated to nanodroplets to reduce the consumption of LM and then modified by 3-mercaptopropionic acid (LMNPS-MPA) to improve the interfacial adhesion between LM and PUS. The denser and even distribution of LMNPS-MPA self-assembling on PDA-treated PUS (PUS-PDA) was successfully prepared via hydrogen bonding interactions. Mechanical sintering of 3D PUS-PDA coated by a two-dimensional (2D) LM layer was then conducted to obtain a continuous conductive network. Comparing with those of the reported 3D conductors, the resulting PUS-PDA-LM composite conductor shows both high electrical conductivity (478 S cm–1) under a low LM consumption of 10 vol% and excellent conductivity stability with the relative resistance change, ΔR/R0, of 2% at 50% strain under stretching deformation. The as-prepared PUS-PDA-LM composites were then successfully applied as flexible and stretchable light-emitting diode (LED) arrays with excellent conductivity and conductivity stability at different deformations. We believe that the 3D stretchable PUS-PDA-LM conductor has many potential applications in flexible sensors, flexible circuits, rollable displays, etc.

Tougheners are crucial for polylactic acid (PLA) because of its inherent brittleness. Among the many available tougheners, biobased and/or biodegradable tougheners are the primary choice. However, increasing PLA toughness typically leads to a trade-off with reduced rigidity or modulus. In this study, biobased and biodegradable thermoplastic vulcanizates (BBTPVs), made from PLA and a polyester elastomer (BBPE), are developed for toughening of PLA. The PLA phase in BBTPV ensures high compatibility with the PLA matrix, while the BBPE rubber phase, with its adjustable cross-linking degree and particle size, allows for controlled stress dissipation. Further, fully biobased and biodegradable PLA composites exhibiting excellent performances are prepared. The elongation at break and notched impact strength of the PLA–BBTPV composite increase by 31 and 12 times, respectively, compared with pure PLA, while its tensile strength remains high (44.5 MPa). This study offers a new approach for preparing fully biobased and biodegradable PLA with high rigidity and flexibility.

Dielectric elastomer generator (DEG), which consists of a dielectric elastomer (DE) film sandwiched between two flexible electrodes (FEs), has the advantages of lightweight, high energy density, and high energy conversion efficiency, providing a simple and feasible solution for harvesting energy from human motion or nature. As crucial constituents of DEG, FEs are expected to possess excellent conductivity and compliance. Nevertheless, there is currently no quantitative characterization method for FE compliance. In addition, the impact mechanism of FE compliance on the energy harvesting performance and fatigue life of the DEG remains unclear. In this study, the dynamic mechanical property (DMP) was used to assess the compliance of FEs, and the quantitative characterization method of FE compliance was proposed. A series of silicone rubber electrodes (SREs) with different DMPs and compliance were designed and prepared, and the impact mechanism of FE compliance on the energy harvesting stability and fatigue life of the DEG was investigated. The results indicate that the key to achieving excellent FE compliance lies in reducing the difference in the magnitude of the complex modulus and phase angle between the FEs and DE, which can significantly reduce interfacial friction and extend the fatigue life of DEG. Benefiting from the enhanced FE compliance, the fatigue life and full-life energy density of the DEG device increase by 20.3 times and 26.4 times, respectively, compared with those of the commonly used carbon-based electrodes.

The dynamic density functional theory has been applied to investigate diffusion dynamics in polymer nanocomposites under shear conditions. According to the time-dependent density relaxations of the test particle and polymer chains, the particle diffusion mode and polymer flow pattern have been quantitatively determined and examined by the reported experimental and computational data. It is shown that a suitable coupling of particle size and particle–polymer interaction can produce the maximum diffusion resistance. More importantly, shear stress can induce the microscopic structure transition in polymer nanocomposites from homogeneous dispersion to microphase separation or ordered layer arrangement. The influence extent of particle size, particle volume fraction, and particle–polymer interaction on the transition has been identified to find the optimum condition to minimize the damage to the overall structure.

We developed a new technique to in situ exfoliate graphite into graphene nanosheets and simultaneously prepare graphene nanosheets/elastomer composites based on the Diels–Alder (DA) reaction under strong shearing force transferred by the hydrogenated nitrile butadiene rubber (HNBR) during melt mixing. To realize the DA reaction, expanded graphite (EG) was used as a diene and maleic anhydride (MA) was chosen as the dienophile. The results show the efficient functionalization and exfoliation of EG into MA-functionalized graphene nanosheets (MAG), the good dispersion of MAG, and the formation of the MAG network structure in MAG/HNBR composites at low content of MAG (∼1 wt %). These result in the significant increase in stress at certain strain and the electrical conductivity of MAG/HNBR composites over that of neat HNBR and EG/HNBR composites with 1 wt % MAG. Unlike the method used in solution, this method could be applied in industry for large-scale preparation of graphene nanosheets and their elastomer composites.

Photothermal-induced self-healable and shape memory materials have drawn much attention due to the rapidly growing technical applications and environmental requirements. As epoxy natural rubber (ENR) is a kind of bio-based elastomer with good mechanical properties, weather resistance, and air impermeability, it is of great significance to incorporate ENR with recyclable, photothermal-induced self-healable and shape memory properties. In this study, we report a simple method to cross-link ENR with dodecanedioic acids (DAs) through esterification reaction, and during the cross-linking process, a little aniline trimer (ACAT, a kind of oligoaniline) was added at the same time. Then, the ENR-DA-ACAT vitrimers that were covalently cross-linked with recyclable, self-healable, and multiple responsive properties were obtained, which also possessed various functions. As a result of the transesterification reactions at elevated temperatures, the ENR-based vitrimers possess the ability to be reprocessed and self-healed, and the mechanical properties could be maintained even after three consecutive breaking/mold pressing cycles. Besides, the vitrimer is also responsive to near-infrared (NIR) light and pH with the introduction of ACAT, and we also find that ACAT can be used as a catalyst to accelerate the transesterification reaction. Moreover, it is demonstrated that the ENR-DA-ACAT vitrimer could also be used to construct the reconfigurable shape memory polymer; the shape fixing ratio and shape recovery ratio are both above 95% in the reconfiguration process, and the multistage shape memory performance can also be achieved by NIR irradiation, which will potentially lead to a wide application for ENR in the field of actuators.

Vitrimer is a new class of polymeric materials which can be reprocessed to any shape while being permanently cross-linked. We designed and synthesized a catalyst-free network with poly(dimethylsiloxane)etherimide (PDMS-NH2), terephthalaldehyde (TA), and tri(2-aminoethyl)amine (TREA) through the condensation reaction between amino groups and aldehyde groups. As a result of the exchange reaction of the dynamic imine bond obtained, this PDMS network exhibits the nature of vitrimer-like material, which is examined by solubility and stress-relaxation experiments, and the relaxation time is as short as 64 s at 130 °C. In addition, the vitrimer-like PDMS is malleable and capable of self-healing, and the mechanical properties can be maintained even after three consecutive breaking/mold pressing cycles. Especially, besides heating, this vitrimer-like PDMS can also be recycled and reshaped at ambient temperature due to the exchange reaction of dynamic imine bond when immersed in water, which will potentially lead to green processing of the elastomers.

The interfacial interaction between nanofillers and elastomer plays an important role in properties of elastomer nanocomposites. Up to now, most methods focus on studying the interphase of elastomer nanocomposites. The filler-elastomer interaction forces have not been directly and quantitatively characterized yet. In this study, the interaction forces at nano-Newton scale between elastomer matrix and silica (SiO2) were directly and quantitatively characterized by using peak force quantitative nanomechanical mapping (PF-QNM) mode of atomic force microscopy (AFM). Three kinds of nitrile butadiene rubber (NBR) molecules with different molecular polarity were first grafted on the AFM tip by using click chemistry. The SiO2(or modified SiO2) were pressed into flat films and worked as substrate. The interaction forces between these NBR layer grafted on AFM tip and SiO2(or modified SiO2) substrate were directly and quantitatively obtained. The results show that as the acrylonitrile content of NBR increasing from 26wt% to 41wt%, the average interaction force of NBR/SiO2increases from 4.5 ± 1.0nN to 7.7 ± 1.1nN and that of NBR/m-SiO2increases from 6.2 ± 1.2nN to 12.9 ± 1.0nN. This study provides guidance in direct and quantitative characterization of filler-elastomer interactions at nano-Newton resolution.

Adaptive mechanical behaviors in nature have inspired the development of synthetic adaptive composites, with those responsive to water particularly relevant for biomedical applications. Polymer nanocomposites containing cellulose nanocrystals (CNCs) are prime examples of water-responsive mechanically adaptive materials. Although CNCs are biobased, the matrixes of these composites are exclusively petroleum-based synthetic elastomers, in sharp contrast to their biological counterparts. In this work, we attempted to probe the possibility of using bioderived rubber(s) as the matrix to fabricate CNC-nanocomposite with water-responsive adaptive mechanical behaviors. Specifically, natural rubber (NR) and epoxidized natural rubber (ENR) were used as the composite matrixes. Our results show that the water-responsive sensitivity and reversibility of ENR composites is much more drastic than that of NR composites. This is attributed to the strong CNC–polymer interaction (hydrogen bonding) for ENR, which leads to better filler dispersion and the formation of an extra CNC–polymer network in addition to the CNC–CNC filler network present in the NR composite. The synergistic effect of the dual networks plays a key role in tuning the mechanical properties and water-responsive sensitivity for various potential biomedical applications. Our study further provides guidance to make use of renewable resources to produce high value added water-responsive nanocomposites.

Dielectric elastomer transducers (DETs), with a dielectric elastomer (DE) film sandwiched between two compliant electrodes, are highly sought after in the fields of soft robotics, energy harvesting, and human–machine interaction. To achieve a high-performance DET, it is essential to develop electrodes with high conductivity, strain-insensitive resistance, and adaptability. Herein, we design an electrode (Supra-LMNs) based on multiple dynamic bond cross-linked supramolecular networks (Ns) and liquid metal (LM), which realizes high conductivity (up to 16,000 S cm–1), negligible resistance changes at high strain (1.3-fold increase at 1000% strain), instantaneous self-healability at ambient temperature, and rapid recycling. The conductive pathway can be activated through simple friction by transmitting stress through the silver nanowires (AgNWs) and cross-linking sites of LM particles. This method is especially attractive for printing circuits on flexible substrates, especially DE films. Utilized as dielectric elastomer generator (DEG) electrodes, it reduces the charge loss by 3 orders of magnitude and achieves high generating energy density and energy conversion efficiency on a low-resistance load. Additionally, serving as sensor (DES) and actuator (DEA) electrodes, it enables a highly sensitive sensing capability and complex interaction.

Highly immiscible blend materials with distinctive and excellent properties play a key role in meeting the application needs, especially in extreme environments, and reactive nanoparticles are used to increase the interface adhesion and optimize the morphology of highly immiscible blending. However, these reactive nanoparticles tend to aggregate and even agglomerate during reactive blending, which significantly deteriorates their compatibilization efficiency. Herein, reactive Janus particles with the epoxy group and various siloxane molecular long chain grafting ratios (E-JP-PDMS) were synthesized using SiO2@PDVB Janus particles (JP) and used as compatibilizers for polyamide and methyl vinyl silicone elastomer (PA/MVQ) blends, which were highly immiscible. The effects of the structure of E-JP-PDMS Janus nanoparticles on their location at the interfaces between the PA and MVQ as well as their compatibilization efficiency for the PA/MVQ blends were investigated. The location and dispersion of E-JP-PDMS at the interfaces were improved by increasing the PDMS content in E-JP-PDMS. The average diameter of the MVQ domains of the PA/MVQ (70/30, w/w) was 79.5 μm and was reduced to 5.3 μm in the presence of 3.0 wt % of the E-JP-PDMS with 65 wt % PDMS. As a comparison, it was 45.1 μm in the presence of 3.0 wt % of a commercial compatibilizer (ethylene-butylacylate-maleic anhydride copolymer, denoted as EBAMAH), which provides a guideline for the design and preparation of efficient compatibilizers for highly immiscible polymer blends.

Dielectric elastomer generator (DEG) can harvest electrical energy from various movement in nature such as human walking and ocean waves. To achieve high energy harvesting performance of DEG, dielectric elastomer (DE) composite with strong interfacial interaction, and thus high electrical breakdown strength (Eb) and long fatigue life (NFL) at high strain is a key. In this study, nano-silica (SiO2)/polymethylvinylsiloxane (PMVS) DE composite with strong interfacial interaction for DEG with extremely high energy density (w), high power conversion efficiency (PCE) and long NFLwas prepared by designing and synthesizing a new polar macromolecule coupling agent (MCA), ester group grafted liquid butadiene rubber using a photoinitiated thiol-ene click reaction. Compared with the common small molecule coupling agent (SCA) modified SiO2(SCA@SiO2)/PMVS composite, the new MCA modified SiO2(MCA@SiO2)/PMVS composite shows much stronger interfacial interaction owing to the largely increased co-crosslinking junction and chain entanglement, resulting in the significantly improved elongation at break and Ebat high strain (400%). As a result, MCA@SiO2/PMVS DEG exhibits an up-to-date highest w(92.2 mJ/cm3) and PCE(35.8%) among the previously reported DEG using unprestretched DE film, and its NFLreaches 141000 times, 3.9 times that of SCA@SiO2/PMVS DEG (36000 times). Thus, MCA@SiO2/PMVS DEG shows the highest full-life generating energy density (9710 J/cm3), 4.8 times and 2427 times that of SCA@SiO2/PMVS DEG and commercial VHB DEG, respectively.

In this study, we obtained dielectric elastomer composites with controllable dielectric and actuated properties by using a biomimetic method. We used dopamine (DA) to simultaneously coat the graphene oxide (GO) and partially reduce GO by self-polymerization of DA on GO. The poly(dopamine) (PDA) coated GO (GO-PDA) was assembled around rubber latex particles by hydrogen bonding interaction between carboxyl groups of carboxylated nitrile rubber (XNBR) and imino groups or phenolic hydroxyl groups of GO-PDA during latex compounding, forming a segregated GO-PDA network at a low percolation threshold. The results showed that the introduction of PDA on GO prevented the restack of GO in the matrix. The dielectric and actuated properties of the composites depend on the thickness of PDA shell. The dielectric loss and the elastic modulus decrease, and the breakdown strength increases with increasing the thickness of PDA shell. The maximum actuated strain increases from 1.7% for GO/XNBR composite to 4.4% for GO-PDA/XNBR composites with the PDA thickness of about 5.4 nm. The actuated strain at a low electric field (2 kV/mm) obviously increases from 0.2% for pure XNBR to 2.3% for GO-PDA/XNBR composite with the PDA thickness of 1.1 nm, much higher than that of other DEs reported in previous studies. Thus, we successfully obtained dielectric composites with low dielectric loss and improved breakdown strength and actuated strain at a low electric field, facilitating the wide application of dielectric elastomers.

Dielectric elastomer generator (DEG), consisting of highly deformable dielectric elastomer (DE) film sandwiched between compliant electrodes, can convert mechanical energy into electrical energy. The widely used carbon grease (CG) electrode has short service life. The conductive rubber electrode is the most promising electrode, but its properties still need to be improved to obtain DEG with high energy density and long life. In this study, thin electrode film of superconducting carbon black (CB)/Polydimethylsiloxane (PDMS) composite with smooth surface, uniform thickness and good dispersion of CB in PDMS matrix was prepared by using solution blending combined with ultrasonication followed by freeze drying and mask scraping technique. The strong interfacial bonding between the electrode and DE substrate was obtained by optimizing CB content and mask scraping technique and by using PDMS in both electrode and DE substrate. High elongation at break, good compliance, high electrical conductivity (EC) and high stability of EC were successfully obtained. Compared with DEG using CG electrode, the energy loss at the same conditions of DEG using the electrodes with 6 wt% CB is reduced by 40.3%, and the harvested energy density (up to 20.5 mJ/cm3) increases by 32%. More importantly, CB/PDMS electrode can withstand 60,000 cycles of stretching under 200% strain, much higher than that reported in previous studies.

Abstract

Controlling the interface interaction of polymer/filler is essential for the fabrication of high-performance polymer composites. In this work, a core–shell structured hybrid (SiO2–GO) was prepared and introduced into an epoxy polymer matrix as a new filler. The incorporation of the hybrid optimized the modulus, strength and fracture toughness of the composites simultaneously. The ultrathin GO shells coated on silica surfaces were regarded as the main reason for the enhancement. Located at the silica-epoxy interface, GO served as an unconventional coupling agent of the silica filler, which effectively enhanced the interfacial interaction of the epoxy/SiO2–GO composites, and thus greatly improved the mechanical properties of the epoxy resin. We believe this new and effective approach that using GO as a novel fillers surface modifier may open a novel interface design strategy for developing high performance composites.

Fiber-reinforced rubber composites (FRRC) are widely used as load-carrying and anti-pressure products. Resorcinol–formaldehyde–latex (RFL) dipping is widely used to improve interfacial adhesion between fiber and rubber in industry. Unfortunately, high volatility and toxicity of RFL do great harm to humans and the environment during the open dipping process. In this work, a phloroglucinol–terephthalaldehyde–latex (PTL) dipping system based on a low-toxic and low-volatile resin was developed to achieve equivalent interfacial adhesion instead of RFL ones. The reaction mechanism, chemical structure, and wettability changes on the Nylon-66 (PA66) fiber surface were characterized. The effect of the phloroglucinol/terephthalaldehyde (P/T) ratio on the dip pick-up, morphology of the fiber surface, and interfacial structure of FRRC was investigated to expound the interfacial adhesion mechanism. At the optimum P/T ratio (1/2.2), a dipping layer with uniform and suitable dip pick-up is achieved on the fiber surface, which ensures the formation of an appropriate graded interfacial layer with enough crosslinking density and modulus, under the synergistic effect of co-vulcanization with rubber, and accordingly strengthens interfacial adhesion. The dipped fiber possesses excellent interfacial adhesion, dynamic fatigue life, and storage stability at the RFL level. This new dipping system is environmentally friendly and easy to scale up without making any change in the process and equipment.

In this study, water-responsive elastomer nanocomposites were designed and prepared by simultaneously introducing cellulose nanocrystals (CNCs) and fibrillar silicate (FS) into epoxidized natural rubber (ENR) via latex compounding followed by in-situ drying and filming. The simultaneous presence of CNCs and FS reduces the dense packing of both FS and CNCs because the initial dispersion of FS and CNCs in the latex is homogeneous and mutually separated, and the interaction between FS and CNCs is weaker than that between CNCs. More importantly, the longer FS forms network framework, and some of the shorter CNCs are assembled with FS through hydrogen bonding interaction, forming the much stronger network in CNC/FS/ENR composites. As a result, CNCs and FS show a synergistic effect on the water-responsive sensitivity. Among various ENR composites with the same volume fraction of fillers, 2CNC/4FS/ENR composite exhibits the strongest network, and its storage modulus and reversible water responsive sensitivity are approximately 11.5 times and 3 times that of 6CNC/ENR composite, respectively.

Isobutylene–isoprene rubber (IIR)/polyamides 12 (PA12) blends are well known for their high gas barrier property and thus find applications in refrigeration hoses, tire inner liners, and so on. Nevertheless, the design and preparation of a good compatibilizer for the IIR/PA12 blend is required because of the poor compatibility between PA12 and the IIR phases. In this study, an efficient reactive compatibilizer, glycidyl methacrylate (GMA)-grafted IIR (IIR-g-GMA) copolymer, and GMA/styrene (St)-grafted IIR (IIR-g-St-GMA) copolymer were produced through the free-radical melt grafting reaction, which were initiated by dicumyl peroxide (DCP). Compared with IIR-g-GMA, IIR-g-St-GMA shows a significantly higher grafting degree because the fast generated, more stable St-grafted IIR macroradicals can act as a “bridge” to connect GMA molecules on IIR macroradicals. The results indicate that reactive compatibilization occurs by the introduction of the copolymer, and the extent of the interfacial reaction and compatibilization effect increases with increasing the copolymer content and the grafting degree of GMA. Nanomechanical mapping images of atomic force microscopy show that the average interfacial thickness of the blend largely increases from approximately 55 to 120 nm after compatibilization with 30 phr IIR-g-St-GMA. Meanwhile, the size of the IIR dispersed phase domains largely decreases from 3 to 5 μm to approximately 0.7 μm after compatibilization with this copolymer. The compatibilization mechanism of the copolymers on IIR/PA12 blends is discussed.

In this study, ester group grafted polymethylvinylsiloxane (PMVS-COCH3) with low elastic modulus (Y) and strong polarizability was synthesized and introduced into thermoplastic polyurethane (TPU) with good mechanical properties, high dielectric constant (εr), and easy recyclability to prepare high performance dielectric elastomer (DE). PMVS-COCH3with high grafting degree and low molecular weight was synthesized via the thiol–ene addition reaction and then was solution blended with TPU at low PMVS-COCH3/TPU blending ratios. The as-prepared blends still exhibit good mechanical properties and relatively high electrical breakdown strength because the low content of insulated PMVS-COCH3phase is dispersed in continuous TPU phase. Both simulation and experimental results indicate that the ester groups on PMVS-COCH3can form hydrogen bonds with TPU, leading to the disruption of C═O/N–H hydrogen bonding between TPU chains and thus enhancing dipole polarizability. Meanwhile, the PMVS-COCH3dispersed phase acts as a soft polar filler in the TPU matrix, resulting in interfacial polarization and lower Y. Both the introduction of interfacial polarizability and the improvement of dipole polarizability largely increase the εrof the blend. The actuated strain under the same electric field of the blends over that of pristine TPU is largely improved. At the blending ratio of 3/7, the actuated strain reaches 6.9% without any prestrains, which is the highest actuated strain among various previously reported TPU-based DEs.

A novel method of constructing nanostructures on the surface of aramid fiber (AF) was demonstrated in this article. Through the π–π* interaction between the aramid nanofiber (ANF) and graphene (G), the G/ANF dispersion stably existed in water. In an alkaline solution of tannic acid (TA) and polyethyleneimine (PEI), a TA/PEI (TP) layer was deposited on the surface of AF to introduce functional groups. Then, the modified AF was impregnated with the G/ANF dispersion to construct surface nanostructures to enhance the interfacial adhesion between the fiber and rubber. The results showed that the H pull-out force of the AF and rubber after impregnating with G, ANF, and G/ANF was increased by 15.3, 21.5, and 84.7%, respectively, compared with the untreated AF. The Raman spectroscopy and SEM results show that there is a π–π* interaction between G and ANF, and the ANFs are firmly attached to the surface of G. The hybrid G/ANF nanofiller can form 3D nanostructures on the surface of AF to improve the mechanical interlocking and stress transfer between the fiber and the rubber matrix, thereby achieving excellent interfacial adhesion while maintaining the excellent mechanical properties of AF.

Dielectric Elastomer Generator (DEG) has been used to harvest energy from reciprocating mechanical motion due to its variable capacitance under tension, and thus it has attracted widespread attention in the last decade. In this study, a cone DEG based on VHB elastomer was developed and its energy harvesting performance was optimized by combining equibiaxial prestretching to cone stretching mode and then tailoring the variables such as the equibiaxial prestretch ratio, input bias voltage and cone displacement. The coupling relationship among these variables and their combined influences on generated energy, energy density and conversion efficiency were systematically studied for the first time. The results indicate that prestretching plays an important role in achieving the target energy harvesting performance at shorter displacement and lower bias voltage, which means lighter weight and portability of the device. More importantly, an up-to-date highest energy density of 130 mJ/g or a maximum electromechanical conversion efficiency of 40% could be obtained by optimizing the variables. In addition, the concept of “displacement threshold” in DEG was firstly proposed and discussed based on leakage and viscoelastic. This work provides ideas for future applications of DEG on portable power and array power generators with high energy harvesting performance.