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Herein, graphene oxide (GO)-encapsulated silica (SiO2) hybrids (GO@SiO2) were prepared via electrostatic self-assembly of the 3-aminopropyltriethoxysilane (APS)-modified SiO2and GO. The as-prepared GO@SiO2was introduced into polydimethylsiloxane (PDMS) elastomer to simultaneously increase the dielectric constant (k) and mechanical properties of PDMS. Then, the in situ thermal reduction of GO@SiO2/PDMS composites was conducted at 180°C for 2 h to increase the interfacial polarizability of GO@SiO2. As a result, the values ofkat 1000 Hz are largely improved from 3.2 for PDMS to 13.3 for the reduced GO@SiO2(RGO@SiO2)/PDMS elastomer. Meanwhile, the dielectric loss of the composites remains low (<0.2 at 1000 Hz). More importantly, the actuated strain at low electric field (5 kV/mm) obviously increases from 0.3% for pure PDMS to 2.59% for the composites with 60 phr of RGO@SiO2, an eightfold increase in the actuated strain. In addition, both the tensile strength and elastic modulus are obviously improved by adding 60 phr of RGO@SiO2, indicating a good reinforcing effect of RGO@SiO2on PDMS. Our goal is to develop a simple and effective way to improve the actuated performance and mechanical strength of the PDMS dielectric elastomer for its wider application. [ABSTRACT FROM AUTHOR]

To meet the growing demand of environmental protection and resource saving, it is imperative to explore bio-based elastomers as next-generation dielectric elastomers (DEs). In this study, we used a bio-based gelatin/glycerin (GG) elastomer as the DE matrix because GG exhibits high dielectric constant ( ɛ r ). Cellulose nanocrystals (CNCs), extracted from natural cellulose fibers, were used to improve the mechanical strength of GG elastomer. The results showed that CNCs with a large number of hydroxyl groups disrupted the hydrogen bonds between gelatin molecules and formed new stronger hydrogen bonds with gelatin molecules. A good interfacial adhesion between CNCs and GG was formed, and thus a good dispersion of CNCs in GG matrix was obtained, leading to the improved mechanical strength of GG. More interestingly, the ɛ r of GG elastomer was obviously increased by adding 5 wt% of CNCs, ascribed to the increase in the polarizability of gelatin chains caused by the disruption of hydrogen bonds of gelatin. As a result, a 230% increase in the actuated strain at low electric field of GG was obtained by adding 5 wt% of CNCs. Since CNCs, gelatin and glycerol are all bio-based, this study offers a new method to prepare high performance DE for its application in biological and medical fields. [ABSTRACT FROM AUTHOR]

In the present study, carboxylated nitrile rubber (XNBR) with high dielectric constant (ε r) and low elastic modulus (Y) was introduced into thermoplastic polyurethane (TPU) with good mechanical properties to prepare macroscopic homogeneous high performance dielectric elastomer (DE) blends. The results show that the XNBR macromolecules can disrupt the N-H/C=O hydrogen bonds of TPU, leading to the increase in dipole polarizability of TPU matrix. On the other hand, the formation of hydrogen bonds between XNBR and TPU increases the interfacial interaction and thus the interfacial polarizability of XNBR/TPU blends. The improvement of both the dipole polarizability and the interfacial polarizability result in the significant improvement of ε r of TPU with increasing the content of XNBR. Meanwhile, the Y of TPU is decreased due to the disruption of hydrogen bonds of TPU and the softening effect of XNBR. The simultaneous increase in ε r and decrease in Y of TPU results in the large increase in electromechanical sensitivity (β) and actuated strain at low electric field of XNBR/TPU blends. Interestingly, the ε r at 103 Hz, the β and the actuated strain at certain electrical field of the blend with XNBR/TPU blending ratio of 80/20 is even higher than that of pure XNBR, which is attributed to the co-continuous structure of this blend as well as the synergetic effect of the increase in dipole polarizability of both TPU and XNBR and the increase in interfacial polarizability. Comparing with our previous study on TPU DE blend by adding low molecular weight plasticizer, XNBR/TPU macromolecular DE blend show better overall performance such as higher mechanical strength, higher breakdown strength and better stability, thus are more likely to be applied in biological and medical fields, where a low electric field is required. Image 1 • Macroscopic homogeneous high performance XNBR/TPU DE blends were prepared. • XNBR disrupts the hydrogen bonds of TPU, increasing the dipole polarizability of TPU. • The formation of XNBR/TPU Hydrogen bonds increases the interfacial polarizability. • The elastic modulus of TPU is decreased by blending with XNBR. • The ε r and actuated strain of XNBR/TPU 80/20 blend is higher than that of pure XNBR. [ABSTRACT FROM AUTHOR]

• A dielectric self-healing elastomer modified by TiO 2 /urea particles was prepared. • The urea on TiO 2 particles can form hydrogen bond with molecular chains. • Synthesized elastomer self-heals mechanical property after 24 h at room temperature. • The TiO 2 /urea particles effectively improve dielectric and actuated performance. • The actuator made of synthesized elastomer can operate again after first breakdown. We designed and prepared a new dielectric self-healing elastomer (TuSE) by introducing the core-shell structured TiO 2 /urea particles into self-healing supramolecular elastomer (SE) assembled by hydrogen bonds. The urea on the outer shell of TiO 2 particles forms hydrogen bonds with the amide groups in the molecular chains, so the TuSE materials exhibit higher self-healing efficiency than SE. The TuSE with 1% TiO 2 /urea particles (TuSE-1%) recovers its mechanical properties within 24 h at room temperature without any external stimulus. Moreover, the TiO 2 /urea particles effectively improve the dielectric constant (ε′) and actuated properties of the supramolecular elastomer. The TuSE-1% exhibits a much higher dielectric constant (ε′ = 16.1 at 1 kHz) and much lower elastic modulus (Y = 0.14 MPa) than those of SE (ε′ = 10.8 and Y = 3.78), resulting in a large increase in electromechanical sensitivity from 2.9 MPa−1 for pure SE to 115 MPa−1 for TuSE-1%. The dielectric elastomer actuator made of TuSE-1% shows a lateral actuation strain of 7.53% at 8.5 V μm−1, 20 times higher than that of pure SE (0.37% at 9 V μm−1). Additionally, TuSE-1% fully recovers its dielectric properties within 24 h, and the actuator can operate again after first breakdown. [ABSTRACT FROM AUTHOR]

Dielectric elastomer (DE) composites have attracted much attention owing to their potential applications such as flexible electronics, energy storage, artificial muscles and sensors. The underlying mechanism to improve the electromechanical performance of DE is believed to be the interfacial polarization between fillers and matrix. Thus, understanding the interfacial polarization mechanism is a key to design and produce high performance DE composites. Despite of extensive works on studying the effect of fillers on interfacial polarization, the role of molecular polarity of matrix is still lacking. Thus, in this study, we prepared three kinds of carbon nanotubes (CNTs)/hydrogenated nitrile butadiene rubber (HNBR) DE composites with different molecular polarity of HNBR as the matrices and a special kind of aligned CNTs as the high dielectric constant (ε′) fillers to study the role of molecular polarity of HNBR on interfacial polarization and dielectric properties of the composites. These composites exhibit the similar dispersion and filler network of CNTs in matrices, which is a precondition of this study. Interestingly, at the same content of CNTs (higher than the percolation threshold), the ε′ of these composites largely increases with the enhancement of the molecular polarity of HNBR, whereas the ε′ of these pure HNBR matrices is very close. An equivalent circuit was then established to quantitatively analyze the interfacial polarization mechanism, and it fits well with the experiment data. This study demonstrates for the first time that the higher molecular polarity of matrix leads to the stronger interfacial polarization and thus results in higher ε′ of the composites. [ABSTRACT FROM AUTHOR]

Thermally reduced graphene oxide (TRG)/thermoplastic polyurethanes (TPU) dielectric elastomer with high dielectric constant ( k ), low dielectric loss and greatly improved actuated strain at low electric field was prepared by solution blending followed by in situ thermal reduction. The results showed that a good dispersion and alignment of TRG in the TPU matrix was obtained. The k at 10 3 Hz was sharply increased from 7 for pure TPU to 1875 for the composite with 2 vol. % of TRG because of the partial restoration of graphite structure and the great increase in dipole polarizability of TPU caused by the disruption of hydrogen bonds of TPU chains. The dielectric loss at 10 3 Hz of the composite with 2 vol. % of TRG remained low (0.43). Despite of the increase in elastic modulus with the increase in the content of TRG, the great increase in k lead to the great increase in electromechanical sensitivity ( β ). As a result, a 106 times increase in β at 10 3 Hz and 17 times increase in actuated strain at low electric field (250 V/mm) were achieved by adding 2.0 vol% of TRG. This study provides a simple and effective method for the improvement of actuated strain at low electric fields through partial reduction of graphene oxide and the disruption of hydrogen bonds in TPU, facilitating the applications of dielectric elastomers in the biological and medical fields, where a low electric field is required. [ABSTRACT FROM AUTHOR]

Abstract: Thermally expanded graphene nanoplates (TGNPs) were introduced into polydimethylsiloxane (PDMS) matrix by using solution mixing method to obtain TGNPs/PDMS dielectric composites with high dielectric constant (k), low dielectric loss and large actuated strain. The results indicated that the k at 103 Hz was obviously increased from 3.1 for pure PDMS to 18.3 and 89.5 for the composite with 1.6wt% and 2.0wt% TGNPs, respectively. Meanwhile, the volume resistivity of all the composites was larger than 109 Ωcm, indicating a low direct current conductance. As a result, the dielectric loss at 103 Hz retained a low value for all the composites. In addition, a significant increase in actuated strain was obtained from 1.4% for pure PDMS to 3.6% with the addition of 2.0wt% TGNPs under a low electric field (15V/μm). The mechanism for the largely improved dielectric properties was carefully discussed based on the uniform dispersion of TGNPs in PDMS matrix, the gradual formation of many parallel or serial micro-capacitor structures (low direct current conductance) with the content of TGNPs increasing, and the remained oxygenic groups coated on TGNPs after high temperature thermal exfoliation. Our work provided a simple, low-cost and effective method to prepare high performance dielectric elastomer (DE), facilitating the wide application of DE composites, especially in the biological and medical fields such as biosensors, artificial muscles, and prosthetics. [Copyright &y& Elsevier]

The application of silicone rubber as dielectric elastomer sensor is limited by its poor strain sensing performance because of low dielectric constant (ε′). In this study, we designed and fabricated a fluorosilicone dielectric composite with high ε′ and capacitive strain sensing performance by designing polar-nonpolar multiblock fluorosilicone copolymer and introducing poly(dopamine)-modified nanotubes (CNT-PDA). Firstly, a polar (bis(3-aminopropyl)-terminated poly(3,3,3-trifluoropropyl) methylsiloxane (H 2 N-PFMS-NH 2)) and a nonpolar (bis(3-aminopropyl)-terminated poly(dimethylsiloxane) (H 2 N-PDMS-NH 2)) silicone oligomers were synthesized by anionic ring opening polymerization. Then, a series of PFMS/PDMS multiblock copolymer were synthesized through a one-pot polycondensation reaction between isocyanate groups from methylene-bis(4-cyclohexylisocyanate) and amino groups from the as prepared H 2 N-PFMS-NH 2 and H 2 N-PDMS-NH 2. The hydrogen bonds between urea groups act as physical crosslinking points on the multiblock copolymer. The H 2 N-PFMS-NH 2 chains with polar CF 3 groups contribute to high dipole polarizability and thus a high ε'. A strong interfacial adhesion between CNT-PDA and the multiblock copolymer was obtained by hydrogen bonding between the urea groups of the multiblock copolymer and CNT-PDA, resulting in strong interfacial polarizability. The as-prepared composite exhibits a ε′ of about 86.7 at 103 Hz and a capacitance change (ΔC) of about 0.91 nF at 200% strain at only 0.3 vol% of CNT-PDA, which was increased by 23.8 and 8.1 times, respectively, compared with the CNT-PDA/commercial nonpolar reference SiR composites. The largely improved ε′ and capacitive strain sensing properties are mainly attributed to the synergistic polarization effect, which was discussed based on impedance analysis and calculating the contribution of each composition on ε' and ΔC. [Display omitted] • A new polar-nonpolar multiblock fluorosilicone was designed and prepared. • A strong interfacial polarizability between CNT-PDA and DE was obtained. • CNT-PDA/fluorosilicone composites can be used as DES. • Both dielectric constant and sensitivity of DES were largely improved. • The relationship between structure and sensitivity was revealed. [ABSTRACT FROM AUTHOR]

• The interfacial cross-linking bonding between E-TiO 2 and PMVS-COOH was formed. • Both dipole and interfacial polarization lead to the large increase in ε′. • The mechanical strength was largely improved due to good interfacial interaction. • The actuated strain at low electrical field was largely improved. Silicone rubber (SiR) is one of the most promising dielectric elastomer (DE) materials for DE actuator, but it is still limited by low properties such as mechanical strength, dielectric constant and actuated strain at low electric fields. In this study, we report the design and preparation of SiR DE composite with simultaneously improved tensile strength, dielectric constant and actuated strain at low electric fields by introducing both polar functional group and multifunctional filler. Firstly, carboxyl groups were grafted onto polymethylvinylsiloxane (PMVS) by using a radical-mediated thiol-ene click reaction to improve the dipole polarizability. Meanwhile, epoxy group-functionalized TiO 2 (E-TiO 2) particles as multifunctional fillers were prepared and filled into carboxyl groups modified PMVS (PMVS-COOH). The esterification reactions between carboxyl groups of PMVS-COOH and epoxy groups of E-TiO 2 results in interfacial covalent cross-linking, good interfacial interaction, and strong interfacial polarizability of E-TiO 2 /PMVS-COOH dielectric composites. As a result, the tensile strength largely increases from 0.33 MPa to 0.89 MPa as the content of E-TiO 2 increases from 10 phr to 30 phr. The dielectric constant at 103 Hz of the composite with 30 phr E-TiO 2 reaches 8.98, which is 3.3 times as reference SiR due to the simultaneously improved dipole and interfacial polarizability. The actuated strain at low electrical field (15 kV·mm−1) of the composite with 30 phr E-TiO 2 reaches 3.7% without any pre-strains, which is 5.2 times than that of reference SiR. Our study provides a simple and effective strategy to simultaneously improve the mechanical, dielectric and actuated properties of SiR DE. [ABSTRACT FROM AUTHOR]