Mechanical,dielectric, and electromechanical properties of silicone dielectric elastomer actuators

Silicone elastomer actuators were investigated to develop a simple and industrially scalable product with improved mechanical properties, such as a low modulus, high tearing strength, and good resilience, and enhanced electromechanical actuation properties. Silicone elastomers were fabricated via a hydrosilylation addition reaction with a vinyl‐end‐functionalized poly(dimethyl siloxane) (V), a multivinyl‐functionalized silicone resin, and a crosslinker in the presence of a platinum catalyst. For the larger electromechanical actuation response, the silicone dielectric elastomer actuator had to have a larger molecular weight of poly(dimethyl siloxane), a smaller hardener content, and a resin‐free composition. However, the silicone elastomer actuators needed to include a small amount of resin to improve the tearing strength. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40030.     

Cauchy stresses and vibration frequencies for the instability parameters of dielectric elastomer actuators

An analysis of the effect of Cauchy stresses, vibration frequency response, and instability on the transient dynamic response of step‐voltage‐driven dielectric elastomer actuators (DEAs) is presented in this paper. Material nonlinearities associated with the hyperelastic constitutive law are taken into account, and the membrane is assumed to be made of an isotropic, homogeneous, and incompressible material. The results for the neo‐Hookean material model are further extended to analyze relatively complex multiparameter hyperelastic models (Mooney–Rivlin and Ogden) that are often employed for investigating the behavior of DEAs. The dynamic instability parameters are predicted using energy‐based extraction of static instability and validated by the response of the material in the vicinity of the dynamic instability. The natural modes of the membrane are used to approximate the nonlinear deformation field using the Galerkin method. A detailed parametric analysis of the equations of motion for the prestretched membrane shows the natural frequencies and mode shapes of the membrane and the strong influence of the stretching ratios and material parameters on the linear and nonlinear oscillations of the membrane. The results of the present investigation show the electric field–frequency relations, resonance curves, and bifurcation diagrams using the nonlinear dynamics of DEAs subjected to electrical loads. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46215.     

Self-assembling structure formation in low-density magnetoactive polymers

The formation of microstructures in magnetoactive polymers (MAPs) is a recently discovered phenomenon found only with very low filler particle concentrations (less than 3 wt %). Due to the degassing process, filler particles collect around an ascending bubble, which dissolves at a certain point leaving particulate rings within the matrix. The formation of toroidal microstructures commences as filler concentration approaches 1 wt %. The development of coherent parallel aligned rings with a compact order continues as particle concentrations increase toward 2 wt %. Between 2 and 3 wt % capillary doublets develop, while mass percentages higher than 3% result in increasing entropy as the random order of particle agglomeration found in higher concentration MAP dominates. Self-structured samples of different filler material and concentrations between 1 and 3 wt % have been investigated using X-ray tomography, where the emerging structures can be observed and visualized. The ring structures resulting from this research represent microinductivities which can be fabricated in a targeted manner, thus enabling new applications in the high-frequency radio field. Furthermore, these anisotropic, but well-organized, structures have magnetic field-dependent implications for optical, thermal, acoustic, and medical applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48291.     

Evaluation of highly compliant magneto‐active elastomers with colossal magnetorheological response

Highly compliant elastomers with a shear storage modulus as low as 25 Pa are prepared using commercially available silicone, plasticizer, and tactile mutator silicone additive. They are used as matrix material for magneto‐active elastomers (MAEs) with carbonyl iron contents between 0 and 85 wt %. In the absence of an external magnetic field, the storage modulus of MAEs based on two selected mixtures ranges between ～100 Pa and ～2000 Pa. Addition of a mutator to the matrix mixture results in a long post‐cure period depending on the curing temperature and the initial mixture. In the presence of a magnetic field, the presented MAEs exhibit a strong magneto‐induced change in storage modulus resulting in a colossal magnetorheological effect of >10⁶ % which is ～30 times higher than previously reported values. The results are of interest in applications using such elastomers as cell substrates with magnetically tunable rigidity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39793.     

石墨烯/室温硫化硅橡胶复合材料的制备及性能

采用水合肼对氧化石墨进行还原获得石墨烯,通过高速剪切分散法将石墨烯分散到α,ω-羟基聚二甲基硅氧烷中,固化后得到石墨烯/室温硫化(RTV)硅橡胶复合材料。对石墨烯和复合材料的微观形貌进行了表征,并考察了复合材料的性能。结果表明,所制备石墨烯的厚度为1～3 nm,为具有较少层数的石墨烯片层结构;复合材料断面呈微相分离结构,但其差示扫描量热曲线只有1个玻璃化转变温度(Tg)。随着石墨烯用量的增加,复合材料的Tg升高,结晶熔点降低。石墨烯对RTV硅橡胶有增强作用,当石墨烯的质量分数为0.5%时,复合材料的拉伸强度达到0.35 MPa,较纯RTV硅橡胶的拉伸强度提高了67%。     

Infrared spectral analysis of low concentration magnetoactive polymers

This work concerns an area of magnetoactive polymer (MAP) research seldom considered. Traditionally only MAP with high concentrations of magnetic filler (typically between 10 and 90 wt%) have been investigated. This article deals with a hitherto neglected aspect of research, namely MAP containing lower magnetic filler concentrations (1 to 3 wt%). This article utilizes a range of spectroscopic analysis methods (Raman and FTIR) and their applicability to MAP characterization at wavelengths ranging from 2.5 to 25 μm. Particular attention is paid to low carbonyl iron particle (CIP) concentrations in MAP for which the emergence of capillary doublets at a critical 2 wt% concentration is revealed. This results in measurable magnetic field-dependent changes in IR absorption at a wavelength of 4.255 μm together with a detectable CO₂ susceptibility. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals Inc. J. Appl. Polym. Sci. 2020 , 137, 48366.     

Silicon core–iron siloxane shell nanoparticle polymer composites with multiferroic properties

Multiferroic (MF) composites based on nanoparticles consisting of a silica core and a shell of spin-variable Fe(III) complexes in a polymer matrix (polystyrene) were synthesized and characterized by different methods. The nanoparticles had the formula 80SiO₂·20{Fe[OSi(Me)(OEt)₂]₃}, and their particle size was on the order of 5–7 nm. Dielectric and electron spin resonance studies showed the presence of two types of Fe ions in the nanocomposite. Iron ions in the low-spin state [Fe(III)-LS] and iron ions in the high-spin state [Fe(III)-HS], which were bound by indirect exchange interactions through oxygen and silicon atoms {[Fe(III)-LS]─O─Si─O─[Fe(III)-HS]} were responsible for the MF properties of the composites with core–shell nanoparticles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47681.     

Performance improvement of piezoelectric‐rubber by particle formation of linear aggregates

We investigate the piezoelectric response of piezoelectric‐rubber consisting of lead zirconate titanate (PZT) particles and silicon rubber prepared by holding it at 100°C for 60 min. Two types of piezoelectric‐rubber were used; one was mixed with PZT particles forming linear aggregates, and the other was mixed with PZT particles forming a random dispersion. The piezoelectric‐rubber whose PZT particles were aligned normal to the rubber surface had much higher piezoelectric effect than the type of piezoelectric‐rubber whose PZT particles were randomly dispersed. The reason for this is that force applied on the former is directly transmitted to PZT particles and the electric charges generated from PZT particles had higher mobility because of the aligned PZT particles, which were connected with each other. As a result, the formation of linear aggregates of PZT particles in rubber was effective in enhancing piezoelectric properties of piezoelectric‐rubber. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39862.     

Enhancement of the rheological properties of magnetorheological elastomer via polystyrene-grafted carbonyl iron particles

In this work, carbonyl iron particles (CIP) was grafted with polystyrene coating on its surface via polymerization method, and the coated-CIPs were then embedded into a silicone rubber with the ratio of 70:30 of CIP to silicone rubber in order to enhance the rheological properties of magnetorheological elastomer (MRE) in terms of lower initial storage modulus and higher MR effect. By using field emission scanning electron microscopy (FESEM) that is equipped with the energy dispersive X-ray spectroscopy for elemental analysis, it was observed that elements of C, N, O, Si, Fe, Br, Cu, and Sn were detected, confirming that the coating layer has been successfully developed on the CIP. Additionally, the investigation of the rheological characteristics was conducted at 25°C with three different sweep conditions using rheometer MCR 302. Firstly the strain amplitude was swept from 0.001% to 10% strain with 1 Hz frequency. Then, the frequency was varied from 1 Hz to 100 Hz under 0.01% strain at an applied current of 0–5 A. Lastly, the current was swept from 0 to 5 A under 0.01% strain amplitude and 1 Hz excitation frequency. It was discovered that the storage modulus of the polystyrene-coated CIP MRE is lower than that of uncoated-CIP MRE in all three sweep profiles. Advantageously, the magnetorheological (MR) effect of the coated-CIP MRE sample is higher than that of the uncoated-CIP MRE by 28.04%. Moreover, it was found that the coated-CIP MRE exhibited higher damping behavior with more than 0.14 loss factor than 0.12 loss factor of the uncoated sample. The dimensional stability of polystyrene coating on the CIP was an attributing factor to this enhanced damping behavior of the coated-CIP MRE. Thus, it became clear that the polystyrene-coated CIP embedment in MRE is more desirable than that of MRE with uncoated CIP.     

Dynamically vulcanized nitrile rubber/polypropylene thermoplastic elastomers

A new compatibilized method was used to prepare thermoplastic elastomer (TPE) of nitrile rubber (NBR) and polypropylene (PP) with excellent mechanical properties by dynamic vulcanization. Glycidyl methacrylate (GMA) grafted PP/amino‐compound was used as a compatibilizer. The effects of the curing systems, compatibilizer, PP type, and reprocessing on the mechanical properties of NBR/PP thermoplastic elastomers were investigated in detail. Experimental results showed that the addition of amino‐compound in the compatibilzer can significantly increase the mechanical properties of the NBR/PP thermoplastic elastomer. Compared with other amino‐compounds, diethylenetriamine (DETA) has the best effect. PP with higher molecular weight is more suitable for preparing NBR/PP thermoplastic elastomer with high tensile strength and high elongation at break. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2862–2866, 2002     

Preparation and electrodeformation of silicone dielectric elastomers containing poly(propylene glycol diacetate) with different molecular weights

In this study, poly(propylene glycol diacetate)s (PPGDAs) with different molecular weights were obtained by the esterification reaction of poly(propylene glycol) and acetic anhydride. We effectively reduced the residual moisture and hydrophilicity of PPGDA. Then, poly(dimethyl siloxane) (PDMS) was modified by the addition of only 5 wt % PPGDA, which possessed a high dielectric constant (k) and a large actuated strain at a low electric field. PPGDA was used to enhance the molecular polarity because of the more polar oxygen atoms and the greater number of ester groups. The great increase in k and the low elastic modulus of the PPGDA–PDMS composites lead to a great increase in the electromechanical sensitivity. When the molecular weight of PPGDA was about 4000, the PPGDA–PDMS composites had the largest actuated strain. As a result, compared to the pure silicone elastomer (8.94%), it exhibited a greater strain of 17.31% at a low electric field of 10.5 V/μm (an increase of ca. 1.94 times). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45329.     

Preparation and properties of magnetorheological elastomers based on silicon rubber/polystyrene blend matrix

Magnetorheological (MR) elastomers, which are mainly composed of magnetic particles and elastic polymer, are a new kind of smart materials whose modulus can be controlled by changing the strength of magnetic fields. In this article, MR elastomers based on immiscible silicon rubber/polystyrene (SR/PS) blend matrix were fabricated successfully via cosolvent method and the MR effect, electric and mechanical properties, and the microstructures of the corresponding materials were studied. SEM studies showed that the dispersion of iron particles in blend matrix were different from that in single polymer, which could be further proved by the different electric conductivity. The MR effect of MR elastomers based on blend matrix varied with the different ratios of SR and PS, which was discussed in detail from the special dispersion of iron particles and of zero‐modulus of MR elastomers. In addition, the MR elastomers based on SR/PS blend matrix had enhanced mechanical properties, which made them more hopeful to be applied in practice. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3143–3149, 2007     

Fabrication and performance of a donut‐shaped generator based on dielectric elastomer

Dielectric elastomers (DEs) have been suggested as generators to harvest electrical energy from natural mechanical energy sources, such as human movements and ocean waves. In this study, a donut‐shaped DE generator (DEG) has been fabricated and its performance is characterized depending on the stretch deformation. A simple new stretchable electrode system using multi‐walled carbon nanotubes has been suggested. Measurements on the resistance, capacitance, and electrical power generation are made depending on the area expansion. The capacitance and harvested energy are parabolically increased with increased area expansions. The theoretical prediction of energy harvesting is in good agreement with measured values of capacitance changes with stretching. FE analysis is also applied for calculation of strains for the DEG to figure out the distribution of strains. It is suggested that the DEG has promising applications in the field of designing an energy harvesting device depending on the type of energy available. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40076.     

Programmable liquid crystal elastomer matrix through photomechanical responses

Considering the dependence of photomechanical responses of liquid crystal elastomers on the director orientation, the performance controlling through director orientation design becomes possible. In this article, a programmable liquid crystal elastomer matrix is proposed to achieve the desired functions. First, a modeling framework about the spontaneous bending of liquid crystal elastomer square plate with arbitrary director orientation is developed. Three kinds of spontaneous bending configurations are obtained along with the variation of the director orientation, and the critical division of the director orientation is given. Based on the deformation characteristic, the director orientation of the liquid crystal elastomer matrix is programmed and several typical prototypical functions, such as 3D code or image display, are discussed. This work provides the guidance for the application of the liquid crystal elastomer in haptic display, braille display, remotely-controlled actuators, and codes.     

Piezoresistive behavior of graphene nanoplatelets/carbon black/silicone rubber nanocomposite

Silicon rubber (SR) filled with carbon black (CB) and carbon black (CB)/graphene nanoplatelets (GNPs) hybrid fillers are synthesized via a liquid mixing method. The effects of filler type on the electrical properties and piezoresistive properties (near the region of the percolation) of the conductive SR composites are studied. It is suggested that the conductivity of the composite filled with CB/GNPs hybrid fillers in the mass ratio of 2 : 4 is much higher than that in other ratio. Percolation threshold for CB/GNPs/SR is found to be 0.18 volume fractions lower than CB/SR. Moreover, force rang and linearity of GNPs/CB/SR is higher than CB alone filling system. And the repeatability of the GNPs/CB/SR composites is better than CB/SR. Not repetitive index () of them is 0.1 and 0.18, respectively. The results suggest that the GNPs/CB/SR composites provide a new route toward fabrication of flexible piezoresistive sensors with high performance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39778.     

Thermal and scanning electron microscopy/energy‐dispersive spectroscopy analysis of styrene–butadiene rubber–butadiene rubber/silicon dioxide and styrene–butadiene rubber–butadiene rubber/carbon black–silicon dioxide composites

Silica as a reinforcement filler for automotive tires is used to reduce the friction between precured treads and roads. This results in lower fuel consumption and reduced emissions of pollutant gases. In this work, the existing physical interactions between the filler and elastomer were analyzed through the extraction of the sol phase of styrene–butadiene rubber (SBR)–butadiene rubber (BR)/SiO₂ composites. The extraction of the sol phase from samples filled with carbon black was also studied. The activation energy (E_a) was calculated from differential thermogravimetry curves obtained during pyrolysis analysis. For the SBR–BR blend, E_a was 315 kJ/mol. The values obtained for the composites containing 20 and 30 parts of silica per hundred parts of rubber were 231 and 197 kJ/mol, respectively. These results indicated an increasing filler–filler interaction, instead of filler–polymer interactions, with respect to the more charged composite. A microscopic analysis with energy‐dispersive spectroscopy showed silica agglomerates and matched the decreasing E_a values for the SBR–BR/30SiO₂ composite well. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2273–2279, 2005     

Superior ammonia sensing properties of PET-supported polyaniline/reduced graphene oxide/zinc ferrite ternary nanocomposite thin film at room temperature

This article introduces a ternary nanocomposite-based flexible thin film ammonia sensor developed on transparent polyethylene terephthalate (PET) substrate in the well-known in situ chemical oxidative polymerization technique. The nanocomposite consists of three different materials: polyaniline (PANI), reduced graphene oxide (rGO), and zinc ferrite (ZF). Keeping the PANI amount constant, seven PANI/rGO/ZF (PRZ) samples are produced by performing stoichiometric variation between rGO and ZF. Later on, various structural, morphological, and spectroscopic analysis of all the composite materials is accomplished with field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible spectroscopy (UV–Vis). The sensing performance of the as-produced sensors toward ammonia (NH₃) is examined in the concentration range from 250 ppb to 100 ppm. The study reveals the excellent sensing ability of the PRZ3 sensor (rGO = 30%, ZF = 20%) achieving minimum and maximum responsivity values of ~51% and ~1052%, respectively, at the lowest (250 ppb) and highest (100 ppm) concentration of ammonia. The sensor also exhibits admirable repeatability, good dynamic responsivity, rapid response (t_res ~2.9–5 s), moderately faster recovery (t_rec ~37.9–69.7 s), superb linearity against ppm variation (R² ~ 0.989), low detection limit (~123 ppb), and exceptional selectivity toward ammonia. The substrate temperature variation divulges that room temperature (30°C) is the ideal temperature for getting outstanding responsivity of the sensor. The study is further accompanied by humidity variation in the incoming air and bending flexibility test of the substrate. A compulsory and legitimate model regarding the sensing mechanism is presented at the end.     

Magnetite/graphene/polyaniline composite for removal of aqueous hexavalent chromium

Here, we report the synthesis of Fe₃O₄/G/PANI composite containing magnetite nanoparticles (Fe₃O₄), graphene sheets (G), and polyaniline (PANI) via chemical route for removal of toxic Cr (VI) from water. TEM image shows the formation of uniformly distributed magnetite nanoparticles on graphene/PANI composite. HRTEM images shows the formation of crystalline magnetite nanoparticles showing lattice fringes with inter‐planner distance 0.21 nm. The magnetic measurement shows magnetization 22 emu/g and ferromagnetic property of the adsorbent. The equilibrium adsorptions were well‐described by the Langmuir isotherm model and shows maximum adsorption capacity 153.54 mg/g at pH 6.5 and temperature 30 °C. The kinetics data well fitted by pseudo‐second‐order model and around 86% Cr (VI) removal completed within 20 min. The Cr (VI) removal capacitive decreases with increase in pH and ionic strength. The adsorbent shows leaching of iron nanoparticles at pH 1 whereas stable in solution having pH 2 and more. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44002.     

A highly flexible,electrically conductive,and mechanically robust graphene/epoxy composite film for its self-damage detection

Advanced functional composites have attracted a great attention for fabricating flexible devices. In this article, the GnP/epoxy composite film was prepared by mixing graphene platelets (GnPs) with epoxy through sonication process. The morphology, mechanical properties, and electrical conductivity of the prepared composites were investigated. As the GnP contents increased from 2.5 to 7.5 vol%, the composites showed an increase in strain sensitivity with the rapid decrease in the strain gauge to 4.4. Additionally, when dynamic movement of the flexible film was performed, at bending and twist angle of 135° and 180°, respectively, steady increase in both resistance changes were detected and compared. The electrical resistance of the flexible was measured over a temperature range of 20–95°C, an increase in temperature lead to a linearly equivalent increase in resistance. The composites can also detect slight pressure changes at 2 kPa compression force with rapid decrease of resistance. Additionally, fatigue test was performed with stable, sensitive, and no distinguishable reading under 2,000 stretching cycles. The composite film exhibits an excellent self-sensing responds when fracture occurred. Thus, the obtained highly flexible, conductive, and mechanical robust composite sensor can be applied as advanced composites sensors for health monitoring.     

Glycerol as high‐permittivity liquid filler in dielectric silicone elastomers

A recently reported novel class of elastomers was tested with respect to its dielectric properties. The new elastomer material is based on a commercially available poly(dimethylsiloxane) composition, which has been modified by embedding glycerol droplets into its matrix. The approach has two major advantages that make the material useful in a dielectric actuator. First, the glycerol droplets efficiently enhance the dielectric constant, which can reach astonishingly high values in the composite. Second, the liquid filler also acts as a softener that effectively decreases the elastic modulus of the composite. In combination with very low cost and easy preparation, the two property enhancements lead to an extremely attractive dielectric elastomer material. Experimental permittivity data are compared to various theoretical models that predict relative permittivity changes as a function of filler loading, and the applicability of the models is discussed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44153.