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In this study, erucamide as a non‐toxic and tasteless lubricant was melt blended with thermoplastic polyurethane (TPU) to reduce the coefficient of friction (COF) of TPU and thus to improve the wearing comfort of intelligent wearable devices. The results show that when the content of erucamide reaches percolation, erucamide can migrate to the TPU surface, forming a layer of lubrication film, and thus significantly reduces the COF of TPU. In addition, erucamide with amide groups can form hydrogen bonds with carbamate groups from TPU chains and thus can disrupt the hydrogen bonds between two amide groups of TPU chains. With the introduction of erucamide, the chain mobility of TPU increases, the partial phase mixing of soft phase and hard phase of TPU occurs, and the interchain interaction between TPU chains decreases. Under the appropriate content of erucamide (0.5 wt%), both the elasticity and processability of TPU are also significantly improved, whereas the high tensile strength, tear strength and elongation at break of the TPU blend is still obtained, facilitating its practical application in intelligent wearable devices. © 2022 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

In this study, moderate content of polyethylene glycol (PEG) with ionic conductivity and low content of graphene oxide (GO) were simultaneously introduced into thermoplastic polyurethane (TPU) followed by in-situ chemical reduction of GO (rGO) to prepare TPU/PEG/rGO dielectric elastomer (DE) composites with largely improved electromechanical performance. The results showed that PEG remarkably disrupted the hydrogen bonds between TPU chains in TPU/PEG/rGO composites and formed new hydrogen bonds with TPU. In addition, PEG molecules can also form hydrogen bonds with rGO, leading to the coating of PEG on GO and thus the separation of rGO from TPU. Interestingly, PEG and rGO showed significant synergistic effect on the dielectric constant ( ε′ ) of the composites, resulting in the large increase in ε′ at 10 3 Hz from 7 for pristine TPU to 71 for TPU/PEG/rGO composite. This was attributed to the increase in dipole polarizability of TPU chains caused by the disruption of hydrogen bonds and the increase in interfacial polarizability caused by the favorable electron transfer from partially reduced GO coated by PEG to TPU. The elastic modulus ( Y ) of the TPU/PEG/rGO composites largely decreased because of the plasticizing effect of PEG and the separation of GO from TPU. Owing to the simultaneous increase in ε′ and decrease in Y , the composite showed 49 times increase in electromechanical sensitivity ( β ) and 6.5 times increase in actuated strain at a certain electric field over that of pristine TPU. [ABSTRACT FROM AUTHOR]

It is a significant but challenging task to simultaneously reinforce and functionalize diene rubbers. Inspired by 'sacrificial bonds', the authors engineer sacrificial hydrogen bonds formed by pendent urazole groups in crosslinked solution-polymerized styrene butadiene rubber (SSBR) via triazolinedione click chemistry. This post-crosslinking modification reveals the effects of the sacrificial bonds based on a consistent covalent network. The 'cage effect' of the pre-crosslinked network facilitates the heterogeneous distribution of urazole groups, leading to the formation of hydrogen-bonded multiplets. These multiplets further aggregate into clusters with vicinal trapped polymer segments that form microphase separation from the SSBR matrix with a low content of urazole groups. The clusters based on hydrogen bonds, serving as sacrificial bonds, promote energy dissipation, significantly improving the mechanical properties of the modified SSBR, and enable an additional wide transition temperature region above room temperature, which endows the modified SSBR with promising triple-shape memory behavior. [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 versatile double‐network (DN) hydrogel with two noncovalent crosslinked networks is synthesized by multiple hydrogen bonding (H‐bonding) interactions. The DN hydrogels are synthesized via a heating–cooling photopolymerization process by adding all reactants of agar, N‐acryloyl glycinamide (NAGA) and N‐benzylacrylamide (NBAA) monomers, UV initiators to a single water pot. Poly(N‐acryloyl glycinamide‐co‐N‐benzyl acrylamide) (P(NAGA‐co‐NBAA)) with a triple amide in one side group is synthesized via UV‐light polymerization between NAGA and NBAA, forming a strong intermolecular H‐bonding network. Meanwhile, the intramolecular H‐bonding network is formed between P(NAGA‐co‐NBAA) and agars. The sol–gel phase transition of agars at 86 °C generates the molecular entanglement network. Such a double network enables the hydrogel high self‐healing efficiency (about 95%), good shape memory ability, and high mechanical strength (1.1 MPa). Additionally, the DN hydrogel is completely crosslinked by multiple hydrogen bonds (H‐bonds) and the physical crosslinking of agar without extra potential toxic chemical crosslinker. The DN hydrogels find extensive applications in the biomedical materials due to their excellent biocompatibility. Poly(N‐acryloyl glycinamide‐co‐N‐benzyl acrylamide)/agar double‐network hydrogels crosslinked by multiple hydrogen bonds are synthesized. The double network gives the hydrogel high self‐healing efficiency (about 95%), high mechanical strength (1.1 MPa), and good shape memory ability. [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]

• A self-healable silicone DE was prepared by constructing supramolecular network. • The actuated strain at low electric field was largely improved. • High self-healing efficiency of tensile strength and actuated strain was obtained. • The silicone DE shows different self-healing mechanism at 80 °C and 100 °C. Dielectric elastomers (DE) suffer from cracks and breaks during repeated cycles, thus a DE material with both high actuated strain (S A) and self-healing ability is highly desired. Herein, for the first time we report a self-healable silicone DE (SiR-SN) with large S A under low electric field by constructing supramolecular network assembled by hydrogen bonds and ionic bonds from two components involving carboxyl modified polymethylvinylsiloxane (PMS-g-COOH) and amino terminated polydimethylsiloxane (PDMS-NH 2). The results show that as PMS-g-COOH content increases, the dielectric constant (ε′) of SiR-SN increases owing to an increase in dipole content whereas the elastic modulus (Y) decreases because of a decrease in crosslinking density, leading to the significantly increased S A at a given electric field. SiR-SN with 0.2/1 of the mass ratio of PMS-g-COOH to PDMS-NH 2 shows much higher ε′ and S A than the commercial silicone DE. Interestingly, self-healing of SiR-SN at 80 °C leads to the re-formation of hydrogen bonds, and thus the recovery of network structure, whereas self-healing at 100 °C can lead to the conversion from hydrogen bonds into ionic ones, and thus the change of network structure. As a result, a self-healing efficiency of 115% in tensile strength and almost 100% in S A at a given electric field can be achieved after self-healing at 80 °C for 5 h, whereas an increase in Y and higher breakdown strength can be achieved after self-healing at 100 °C, which may sustain the repeated stress and prolong the service life. It is promising that this new self-healable silicone dielectric elastomer with large actuated strain under low electric field could be used especially in biological and medical fields. [ABSTRACT FROM AUTHOR]