Silicone Dielectric Elastomer Research Articles

Room-temperature self-assembly of poly-(thioctic acid)/silicone dielectric elastomer for highly healable, transparent, electro-sensitive electronic actuator

The emergence of dielectric elastomers (DEs) is significant for various electric applications. However, limited by expensive raw materials and complex preparation methods, existing DEs cannot combine functionality, especially self-healing ability, and commercial feasibility. Here we report the facile synthesis of autonomous self-healable dielectric elastomers (ASH-DEs) assembled from thioctic acid (TA), 3-aminopropyltrimethoxysilane (APS) and silicon oil. Particularly, via the covalent bonds and multiple H-bonds, this process ingeniously enabled the spontaneous ring-opening polymerization of polar monomer TA in non-polar silicon based DEs at room temperature without solvent to form stable polyTA for the first time. The obtained ASH-DEs exhibits widely tunable dielectric and mechanical properties, high transparency, room-termperature self-healing capability, and strain sensitivity at low electric fields. The applications of ASH-DEs as muscle-like highly durable and sensitive large-strain actuators are further certified, proving the elastomer's huge potential in the emerging field of flexible electronics and devices.

Soft Pocket Pump for Multi‐Medium Transportation via an Active Tubular Diaphragm

AbstractRecent developments in small and agile multifunctional autonomous robots, portable and wearable drug delivery devices, and implantable ventricular assist devices have increased the demands for a new class of small and soft pumps that can conform to irregular or even deformable robotic bodies or human organs. In this work, a dual‐chamber pocket‐sized pump with a tubular diaphragm made of multilayered silicone dielectric elastomer actuators, three miniature check valves, and an outer shell is proposed. Dielectric elastomer actuators diaphragm holds well dynamic performances that resonate at 230 Hz, which leads to a no‐load flow rate of 340 mL min−1 and back pressure of 7.5 kPa, with the pump's total volume as only 2.36 cm3 and weight as 2.4 g. Besides, the proposed pump can be bent up to 60° with a negligible drop in its pressure and flow rate. The pump's capability to pump air, water, and its seamless switch is demonstrated. By tuning the amplitude of the driving voltage, the pump's pressure can be precisely controlled. This highly flexible and compact pump can be a potential candidate for driving small robots and biomedical devices.

Preparation and characterization of CNTs/CaCu3Ti4O12/silicone rubber composites with improved dielectric and mechanical properties

AbstractThe dielectric performance of Silicone rubber (SR) composites can be significantly enhanced by carbon nanotubes. However, carbon nanotubes are easy to agglomerate in the polymer matrix. Adding low‐dimensional materials of different dimensions may be a solution. In this article, one‐dimensional multiwall carbon nanotubes (CNTs) and zero‐dimensional copper calcium titanate (CaCu3Ti4O12, CCTO) ceramic fillers were simultaneously added to prepare silicone dielectric elastomer composites. SEM results showed that the CNTs were distributed uniformly in the SR matrix due to the addition of CCTO. When 2 wt% CNTs and 10 wt% CCTO were added, the dielectric constant of the composite increased from 2.79 (pure silicone rubber) to 5.72, with a low loss tangent of 0.0012. Due to the uniform dispersion of CNTs with the addition of CCTO particles, dielectric performance of the composites were enhanced. The tensile stress was 986 kPa, the elongation at break was 333%, while the elastic modulus was not more than 613 kPa (2 wt% CNTs and 5 wt% CCTO in the SR composite). In addition, the composites had a wide temperature range up to 400°C. Therefore, the prepared CNTs/CCTO/SR composites have good dielectric and mechanical properties, and good thermal stability. It has a good reference value for this kind of composites as dielectric elastomer materials.

Modelling the electromechanical sensitivity of silicone composites using response surface methodology

Dielectric elastomers are used for sensor and actuator applications. These materials convert voltage applied directly into strain through Maxwell stress. An important parameter in the determination of voltage induced strains is electromechanical sensitivity. This paper presents an approach to establish the model for predicting the electromechanical sensitivity of silicone dielectric elastomer composites using the response surface methodology. Two-factor and two-level, face-cantered composite design is used for experimentation. The parameters which affect the electromechanical sensitivity are selected as superconducting carbon black (SCCB) and barium titanate (BT). Response surface methodology is used to derive second-order quadratic model with interactions. Investigation showed that SCCB has more significant effect than parameter BT, on controlling the electromechanical sensitivity of these composites. Maximum electromechanical sensitivity for these composites was found at around ≤ 4 parts per hundred weight fractions for both the parameters.

Silicone Dielectric Elastomers with Incorporation of Different Types of Filler as Smart Materials for Wave Energy Harvester

Silicone Dielectric Elastomers with Incorporation of Different Types of Filler as Smart Materials for Wave Energy Harvester

Ternary silicone dielectric elastomer micro‐nanocomposites with enhanced mechanical and electromechanical properties

AbstractIn this paper, ternary silicone dielectric elastomer micro‐nanocomposites were prepared by mixing barium titanate (BT) nanoparticles or 3‐mercaptopropylethoxy‐bis(tridecyl‐pentaethoxy‐siloxane) (Si747)‐modified BT (BT‐Si747) with hexagonal boron nitride (BN) microplatelets into methyl vinyl silicone rubber (MVSR). BN platelets as physical barriers improve the dispersion of BT nanoparticles, so the MVSR/BT/BN composites achieve the higher electric breakdown field. The Si747 in MVSR/BT‐Si747/BN composites can be grafted on BT nanoparticles surface while the mercapto groups of Si747 can react with double bonds of MVSR, which increases interfacial interaction to improve the mechanical property. As a result, the tensile strength and elongation at break of MVSR/30 wt%BT‐Si747/30 wt%BN composite are 3.43 MPa and 2705%, which is 2.4 and 4.4 times as high as the MVSR/30 wt%BT/30 wt%BN composite, respectively. The MVSR/BT‐Si747/BN composites exhibit higher actuation performance under lower electric fields due to simultaneous increase in dielectric constant and decrease in elastic modulus. The MVSR/10 wt%BT‐Si747/10 wt%BN composite obtains an actuated strain of 8.81% at 47.48 kV/mm, which is twice as high as pure MVSR (4.4% at 60.21 kV/mm). The used method in this experiment is simple, effective, and low cost, and prepared ternary micro‐nanocomposites have potential applications in dielectric actuators.

A dipolar silicone dielectric elastomer and its composite with barium titanate nanoparticles

This paper offers a simple, low-cost, and effective method to prepare high-performance dielectric elastomer. 4-chorophenethyl alcohol as dipole functionalizes crosslinker and then the functional crosslinker is utilized to prepare a novel dipolar silicone elastomer (SRCl). The introduction of dipole reduces regular arrangements of molecular chains and the dispersive crosslinking is formed in SRCl. The dipolar crosslinkers are evenly distributed in the crosslinking network, so the mechanical, dielectric, and electromechanical properties are improved. The dielectric elastomer actuator made of the SRCl with 15% dipoles exhibits a maximum actuated strain of 9.97% and the SRCl with 12% dipoles shows the highest breakdown field strength of 73.33 V/μm, which is increased by 156% and 52%, respectively, compared with pure silicone elastomer (SR, 3.89% at 48.23 V/μm). In addition, barium titanate (BT) nanoparticles as filler is mixed with SRCl to prepare the SRCl/BT composites. It is found that the dielectric property of composites is dominated by the matrix polarity. The electrostatic interaction between hydroxyl groups on BT nanoparticles and chlorine groups on the SRCl matrix improves the dispersion of BT nanoparticles in SRCl matrix. The maximum actuated strain of SRCl/20% BT (11.97%) is 3 times as high as SR (3.89%).

A supramolecular silicone dielectric elastomer with a high dielectric constant and fast and highly efficient self-healing under mild conditions

A silicone dielectric elastomer with simultaneous high dielectric constant, fast and efficient self-healing ability at mild conditions was prepared by constructing supramolecular network assembled by coordination bonds and hydrogen bonds.

Compatibilization of porphyrins for use as high permittivity fillers in low voltage actuating silicone dielectric elastomers.

Polysiloxanes represent, because of their unusual properties, a material with great potential for use in dielectric elastomers (DEs), a promising class of electroactive polymers. Currently, their application as actuators is limited by the need for high driving voltages, as a result of the low relative permittivity possessed by polysiloxanes (∼2–3). Reducing these voltages can be achieved to some degree by using high permittivity additives to improve the permittivity of the polysiloxane. However, modifying such additives so that they are compatible with, and can be dispersed within, polysiloxane elastomers remains challenging. For reliable actuation, full miscibility is key. In this work the porphyrin 5,10,15,20-(tetra-3-methoxyphenyl)porphyrin (TPMP) was investigated as a high permittivity additive. Its behaviour was compared to the analogue that was derivatized with bis(trimethylsiloxy)methylsilane groups using the Piers–Rubinsztajn reaction to improve compatability with silicone formulations. The derivatized porphyrin was dispersed in elastomers and their dielectric and mechanical properties were evaluated. It was discovered that only low levels of incorporation (1–10%) of the siliconized TPMP – much lower than the parent TPMP – were needed to elicit improvements in the permittivity and electromechanical actuation of the elastomers; actuation strains of up to 43% could be achieved using this method.

Silicone dielectric elastomers optimized by crosslinking pattern – a simple approach to high-performance actuators

Chemical design of silicone elastomers for improving the electromechanical response of dielectric elastomer actuators.

Silicone dielectric elastomer with improved actuated strain at low electric field and high self-healing efficiency by constructing supramolecular network

Dielectric elastomers (DE) suffer from cracks and breaks during repeated cycles, thus a DE material with both high actuated strain (SA) and self-healing ability is highly desired. Herein, for the first time we report a self-healable silicone DE (SiR-SN) with large SA 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-NH2). 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 SA at a given electric field. SiR-SN with 0.2/1 of the mass ratio of PMS-g-COOH to PDMS-NH2 shows much higher ε′ and SA 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 SA 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.

Optimization of an electret-based soft hybrid generator for human body applications

Hybridization of two electroactive materials could be the key to design soft innovative generators able to scavenge mechanical energy from human movement. Among all the technologies, soft electret generators based on charges recombination between two electrodes through an external resistive load, are promising soft hybrid generators with a theoretically scavenged energy density up to 1.42 mJ g−1. In order to reach high level of scavenged energy, we present here an optimization of an electret-based hybrid structure regarding the mechanical architecture but also the material used and especially the electret involved. A smart optimized frame insures a perfect coupling between the silicone dielectric elastomer (Sylgard 186) and the electret polymer (Teflon) while maximizing the capacitance variation and minimizing the von Mises stresses. This hybrid structure is able to scavenge up to 49 μW on an optimal load of 150 MΩ at 1 Hz and under an applied strain of 50%, with an electret charged up to −1000 V. Parylene C, VT-4 and AF-4 are also investigated as potential electret material underlying an increase of 35% in the output performances of the hybrid structure. The devices structure, operating principles and experimental performance will be presented and discussed, together with the possible improvements to enhance the performance of the devices.

Effect of actuation parameters and environment on the breakdown voltage of silicone dielectric elastomer films

This paper presents results on dielectric breakdown studies for silicone dielectric elastomer (DE) membranes. Dielectric breakdown is a crucial property for the characterization of DE actuator behaviour. Here, we particularly focus on the effect of environmental parameters on the breakdown field, using a recently designed novel test stand for automatic testing of multiple measurement points per sample in a climate chamber. We present an extensive study about the influence of temperature, humidity, and water content on the breakdown field of DEs under indoor environmental conditions. Additionally, the effect of actuation parameters, such as various stretch-ratios, as well as the influence of screen-printed carbon black electrodes, is systematically investigated. The study indicates slightly higher breakdown fields with increasing temperatures but negligible influence of humidity and water content changes. Samples with printed electrodes show significantly lower breakdown fields whereas the increase of stretch ratio resulted in significantly higher breakdown fields.

High actuated performance MWCNT/Ecoflex dielectric elastomer actuators based on layer-by-layer structure

A layer-by-layer structure was constructed by alternately arranging conductive layers and insulating layers in a silicone dielectric elastomer (Ecoflex) to largely improve the actuated strain at a low electric field. In the electric field environment, the insulating layer blocks the transmission channel of electrons in the adjacent conductive layer, so the interfaces of adjacent conductive layers and insulating layers can accumulate and store a large number of charges, thereby greatly increasing the dielectric constant of the material. Meanwhile, the individual conductive layers are separated by an insulating layer to avoid causing large conductance losses. A high actuated strain (20.33%) at a relatively low electric field (12.5 kV mm−1) and good cyclic stability are obtained on the actuator without any pre-strain. These results demonstrate that our research provides a simple and effective method to significantly improve the actuated strain at a low electric field of DE and promote its practical application.

The role of dipole structure and their interaction on the electromechanical and actuation performance of homogeneous silicone dielectric elastomers

Grafting polar groups onto elastomer chains has proven to be an effective method to achieve high performance homogeneous dielectric elastomers (DE). Up to now, there still lacks an in-depth understanding of the effect of structure and content of these grafted dipoles on the electromechanical properties of the modified DE. In this study, three kinds of polar groups including carboxyl (COOH), hydroxyl (OH), and ester (COOCH3) were grafted onto polymethylvinylsiloxane (PMVS) by using a photochemical thiol-ene reaction to prepare PMVS-COOH, PMVS-OH and PMVS-COOCH3 DE. Three grafting degrees (15%, 50% and 95%) were prepared for each kind of modified PMVS. Interestingly, although the dipolar moment of COOH is higher than that of OH and COOCH3, at the same grafting degree, the dielectric constant of PMVS-OH is much higher than that of PMVS-COOCH3 and PMVS-COOH. At high grafting degree (50% and 95%), the actuated strain at a specific electric field of PMVS-OH is significantly higher than that of PMVS-COOH and PMVS-COOCH3. The actuated train at 15 kV/mm sharply increases from 0.2% for PMVS to 9.1% for PMVS-OH with the grafting degree of 95%, higher than that of the commercial silicone DE and the new structured silicone DE reported previously. These dielectric, mechanical and actuated properties are affected by the combined effects of moment, mobility and interactions of these dipoles, which have been deeply discussed. The present study provides guidance for the preparation of high-performance homogeneous DE by rational designing the dipolar structure and content.

Simultaneously improved dielectric and mechanical properties of silicone elastomer by designing a dual crosslinking network

A homogenous silicone dielectric elastomer with simultaneously improved dielectric and mechanical properties is synthesized by designing a dual crosslinking network.

Improved electromechanical properties of silicone dielectric elastomer composites by tuning molecular flexibility

Silicone rubber (SR) composites exhibited significantly improved electromechanical properties via tuning the molecular flexibility by adding plasticizer. To decrease the enhanced elastic modulus of SR composites filled with high-dielectric-constant BaTiO3 (BT) particles, silicone oil (SO) plasticizer was incorporated into the BT/SR composite to weaken the intermolecular interactions and break the structure of the filler network as result of swelling effect. The obviously decreased elastic modulus resulted in a high electromechanical sensitivity β and a relatively large actuated strain of 10.6% for 20 phr BT/SR composite filled with 50 phr SO at a low electric field of 25 kV/mm, approximately 380% increase compared to that of pure SR at the same electric field. The result indicates that tuning flexibility of composites is a good strategy to obtain high-performance dielectric elastomers.

Inkjet 3D printing of UV and thermal cure silicone elastomers for dielectric elastomer actuators

Dielectric elastomer actuators (DEAs) are an attractive form of electromechanical transducer, possessing high energy densities, an efficient design, mechanical compliance, high speed, and noiseless operation. They have been incorporated into a wide variety of devices, such as microfluidic systems, cell bioreactors, tunable optics, haptic displays, and actuators for soft robotics. Fabrication of DEA devices is complex, and the majority are inefficiently made by hand. 3D printing offers an automated and flexible manufacturing alternative that can fabricate complex, multi-material, integrated devices consistently and in high resolution. We present a novel additive manufacturing approach to DEA devices in which five commercially available, thermal and UV-cure DEA silicone rubber materials have been 3D printed with a drop-on-demand, piezoelectric inkjet system. Using this process, 3D structures and high-quality silicone dielectric elastomer membranes as thin as 2 μm have been printed that exhibit mechanical and actuation performance at least as good as conventionally blade-cast membranes. Printed silicone membranes exhibited maximum tensile strains of up to 727%, and DEAs with printed silicone dielectrics were actuated up to 6.1% area strain at a breakdown strength of 84 V μm−1 and also up to 130 V μm−1 at 2.4% strain. This approach holds great potential to manufacture reliable, high-performance DEA devices with high throughput.

A combination of silicone dielectric elastomer and graphene nanosheets for the preparation of bending flexible transducers

A newly developed dielectric elastomer (DE) bending transducer composed of a functionalized graphene-silicone DE composite sandwiched between two graphene flexible electrode layers had been investigated. This bending transducer displayed high actuation displacement (5.3mm) under 2500V direct-current electric field. Compared with pure silicone DE, the silicone DE filled with silane coupling agent functionalized graphene nanofillers showed enhanced dielectric constant, and low loss modulus. The silane coupling agent functionalization method is simple, green, and easy to control, and can be used asa general strategy for improving the dielectric and electric actuated strain of DE.

Fabrication and Test of an Inflated Circular Diaphragm Dielectric Elastomer Generator Based on PDMS Rubber Composite.

This paper introduces a fabrication method and the experimental characterization of a soft polymeric energy converter manufactured using a combination of dielectric and conductive polydimethylsiloxane elastomers. The presented system is an inflated circular diaphragm dielectric elastomer generator; i.e., a deformable electrostatic transducer that converts the mechanical work done by a time-varying pressure into electricity. A prototype of the system is realized on the basis of a simple fabrication procedure that makes use of commercially available silicone dielectric elastomer films and custom-prepared deformable conductive electrodes. A test-bench is developed and employed to estimate the energy conversion performance. Remarkable results are obtained, such as an amount of energy converted per cycle of up to 0.3 J, converted power of up to 0.15 W, energy per unit of employed elastomer mass of up to 173 J/kg, and fraction of the input mechanical work converted into electricity of 30%.