Abstract: The dynamic performance of dielectric elastomer transducers and their capability of electromechanical energy conversion are affected by dissipative processes, such as viscoelasticity, dielectric relaxation, and current leakage. This paper describes a method to construct a model of dissipative dielectric elastomers on the basis of nonequilibrium thermodynamics. We characterize the state of the dielectric elastomer with kinematic variables through which external loads do work, and internal variables that measure the progress of the dissipative processes. The method is illustrated with examples motivated by existing experiments of polyacrylate very-high-bond dielectric elastomers. This model predicts the dynamic response of the dielectric elastomer and the leakage current behavior. We show that current leakage can be significant under large deformation and for long durations. Furthermore, current leakage can result in significant hysteresis for dielectric elastomers under cyclic voltage.

Abstract: In materials research, the development of polymer nanocomposites (PN) is rapidly emerging as a multidisciplinary research field with results that could broaden the applications of polymers to many different industries. PN are polymer matrices (thermoplastics, thermosets or elastomers) that have been reinforced with small quantities of nano-sized particles, preferably characterized by high aspect ratios, such as layered silicates and carbon nanotubes. Thermal analysis (TA) is a useful tool to investigate a wide variety of properties of polymers and it can be also applied to PN in order to gain further insight into their structure. This review illustrates the versatile applications of TA methods in the emerging field of polymer nanomaterial research, presenting some examples of applications of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA) and thermal mechanical analysis (TMA) for the characterization of nanocomposite materials.

Abstract: Far greater voltage-actuated deformation is achievable for a dielectric elastomer under equal-biaxial dead load than under rigid constraint usually employed. Areal strains of 488% are demonstrated. The dead load suppresses electric breakdown, enabling the elastomer to survive the snap-through electromechanical instability. The breakdown voltage is found to increase with the voltage ramp rate. A nonlinear model for viscoelastic dielectric elastomers is developed and shown to be consistent with the experimental observations.

Abstract: To fully exhibit the potentials of the fascinating characteristics of graphene oxide (GO) in polymer, the achievement of strong interface interactions and fine dispersion of GO in the hybrids is essential. In the present work, the elastomeric hybrids consisting of GO sheets are fabricated by utilizing butadiene–styrene–vinyl pyridine rubber (VPR) as the host through co-coagulation process and in situ formation of an ionic bonding interface. The VPR/GO composites with a normal hydrogen bonding interface are also prepared. The mechanical properties and gas permeability of these hybrids with an ionic bonding interface are obviously superior to those of the composites with a hydrogen bonding interface. With the ionic interfacial bonding, inclusion of 3.6 vol% of GO in VPR generates a 21-fold increase in glassy modulus, 7.5-fold increase in rubbery modulus, and 3.5-fold increase in tensile strength. The very fine dispersion of GO and the strong ionic interface in the hybrids are responsible for such unprecedented reinforcing efficiency of GO towards VPR. This work contributes new insights on the preparation of GO-based polymer hybrids with high performance.

Abstract: The performance of dielectric elastomer actuators is limited by electrical breakdown. Attempts to measure this are confounded by the voltage-induced thinning of the elastomer. A test configuration is introduced that avoids this problem: A thin sheet of elastomer is stretched, crossed-wire electrodes are attached, and then embedded in a stiff polymer. The applied electric field at breakdown, EB, is found to depend on both the deformed thickness, h, and the stretch applied, λ. For the acrylic elastomer investigated, the breakdown field scales as EB = 51 h − 0.25 λ 0.63. The test configuration allows multiple individual tests to be made on the same sheet of elastomer.

Abstract: Strength and toughness are commonly two contradictory properties in polymer materials. For polymer elastomers, the addition of stiff filler frequently results in enhanced stiffness but reduced toughness and ductility. Inspired by biomimetic studies, here we demonstrate a new method that can simultaneously improve strength and toughness while maintaining the good ductility of polyurethane elastomers. This method constructs sacrificial bonds and hidden lengths at the interface of graphene nanosheet/polyurethane (GN/PU) composites by exploiting covalently and non-covalently functionalized GNs (HO-GNs). GNs are prepared by reduction of graphene oxide with hydrazine. The residual functional groups such as hydroxyl and epoxide groups on GNs enable PU oligomer chains to be covalently bonded to GNs by sequentially reacting with diisocyanate and polyethylene glycol oligomer. Non-covalently bonded PU oligomer chains are formed by the π–π interaction between GNs and pyrene derivatives. Both Fourier transform infrared spectra and thermogravimetric results provide direct evidence for the covalent bonding in HO-GNs while fluorescence spectra and decay curves confirm the existence of non-covalent bonding. The resulting HO-GNs exhibit a good dispersion capacity in organic solvents and the PU matrix, improving the load transfer and the particle mobility in GN/PU composites. Upon loading, both rupture of the π–π interaction (sacrificial bonds) and release of the hidden length (dissociation of H-bonds between the PU oligomer and polymer chains) enable the composite to exhibit high toughness and ductility nearly identical to the neat polyurethane (strain at break >900%). This approach is expected to be helpful for developing novel strong, tough and highly ductile polymer elastomers.

Abstract: Preparation of Liquid Crystalline Elastomers, by F. Brommel, D. Kramer, H. Finkelmann.- Applications of Liquid Crystalline Elastomers, by C. Ohm, M. Brehmer and R. Zentel.- Liquid Crystal Elastomers and Light, by Peter Palffy-Muhoray.- Electro-Opto-Mechanical Effects in Swollen Nematic Elastomers, by Kenji Urayama.- The Isotropic-to-Nematic Conversion in Liquid Crystalline Elastomers, by Andrija Lebar, George Cordoyiannis, Zdravko Kutnjak and Bostjan Zalar.- Order and Disorder in Liquid-Crystalline Elastomers, by Wim H. de Jeu and Boris I. Ostrovskii.-

Abstract: A combination of experiment and theory shows that dielectric elastomers exhibit complex interplay of nonlinear processes. Membranes of a dielectric elastomer are prepared in various states of prestretches by using rigid clamps and mechanical forces. Upon actuation by voltage, some membranes form wrinkles followed by snap-through instability, others form wrinkles without the snap-through instability, and still others fail by local instability without forming wrinkles. Membranes surviving these nonlinear processes are found to attain a constant dielectric strength, independent of the state of prestretches. Giant voltage-induced stretch of 3.6 is attained.

Abstract: For many applications of dielectric elastomer actuators, it is desirable to replace the carbon-grease electrodes with stretchable, solid-state electrodes. Here, we attach thin layers of a conducting silicone elastomer to prestrained films of an acrylic dielectric elastomer and achieve voltage-actuated areal strains over 70%. The influence of the stiffness of the electrodes and the prestrain of the dielectric films is studied experimentally and theoretically.

Abstract: Gecko-inspired arrays of micropillars made of a liquid crystalline elastomer display thermoswitchable adhesive behavior as a consequence of elongation changes caused by reorientation of the mesogens at the nematic-isotropic (N-I) phase transition.

Abstract: Biomass feedstock is a viable alternative to finite fossil fuel resources to provide many of the same—plus others that petrochemicals cannot—chemical building blocks required to fabricate durable and high-performance materials. We demonstrate here for the first time a new generation of synthesized elastomers, namely bio-based engineering elastomers (BEE). These are of particular significance because they are synthesized from monomers derived from biomass, by routes which are suitable for large scale production, and they exhibit thermo-mechanical properties at least equivalent to current commercial petrochemical-derived elastomers. Bio-based monomers in large scale production, such as sebacic acid, itaconic acid, succinate acid, 1,3-propanediol, and 1,4 butanediol are chosen to generate the first synthetic BEE matrix through melting polycondensation—a comparatively simple reaction scheme offering good control and the potential for low cost, large-scale production. A novel linear BEE, an almost non-crystalline copolyester elastomer with low glass transition temperature (Tg) containing double bonds is designed and synthesized using multiple monomers (to help suppress crystallization). Silica nanoparticles are then introduced into the BEE matrix to achieve significant strengthening and improved environmental stability. Chemical crosslinks formed by peroxide and the pendant double bonds in the copolyester macromolecules endow the BEE with both the necessary high elasticity and required environmental stability. The BEE nanocomposites obtained exhibit excellent thermomechanical properties, such as an ultimate tensile strength of 20 MPa.

Abstract: By using long single-walled carbon nanotubes (SWNTs) as a filler possessing the highest aspect ratio and small diameter, we mimicked the chain structure of polymers in the matrix and realized a highly conductive elastomeric composite (30 S/cm) with an excellent mechanical durability (4500 strain cycles until failure), far superior to any other reported conductive elastomers. This exceptional mechanical durability was explained by the ability of long and traversing SWNTs to deform in concert with the elastomer with minimum stress concentration at their interfaces. The conductivity was sufficient to operate many active electronics components, and thus this material would be useful for practical stretchable electronic devices.

Abstract: Magnetorheological elastomers (MREs) belong to the new group of the functional materials called “smart”. Although smart materials are known since long time, their intensive development started in the end of the XXth century. The term smart materials, intelligent materials or less frequently used adaptive materials or multifunctional materials, was introduced in the eighties of the twentieth century, when some materials, which were included in the group were already known. Till today there is no accepted universal definition of smart material, it is also not included in the encyclopedia devoted to these materials, published in 2002 [1, 2].

Abstract: We demonstrate the use of functionalized graphene sheets (FGSs) as multifunctional nanofillers to improve me- chanical properties, lower gas permeability, and impart electri- cal conductivity for several distinct elastomers. FGS consists mainly of single sheets of crumbled graphene containing oxy- gen functional groups and is produced by the thermal exfolia- tion of oxidized graphite (GO). The present investigation includes composites of FGS and three elastomers: natural rub- ber (NR), styrene-butadiene rubber, and polydimethylsiloxane (PDMS). All of these elastomers show similar and significant improvements in mechanical properties with FGS, indicating that the mechanism of property improvement is inherent to the FGS and not simply a function of chemical crosslinking. The decrease in gas permeability is attributed to the high as- pect ratio of the FGS sheets. This creates a tortuous path mechanism of gas diffusion; fitting the permeability data to the Nielsen model yields an aspect ratio of � 1000 for the FGS. Electrical conductivity is demonstrated at FGS loadings as low as 0.08% in PDMS and reaches 0.3 S/m at 4 wt % loading in NR. This combination of functionalities imparted by FGS is shown to result from its high aspect ratio and carbon-based structure. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 910-916, 2012

Abstract: Iron is the most abundant transition metal in the Earth s crust. As such, it is potentially useful for catalysts that can be employed in high-volume processes, like the Haber–Bosch process that functions with iron oxide as the precatalyst. Maintaining the economic and environmental benefit of iron catalysis, well-defined molecular iron catalysts provide the opportunity to also control selectivity, such as stereoselectivity, during catalysis, if the ligands employed are appropriately selected. Here we report on the iron-catalyzed polymerization of 1,3-dienes to afford elastomers with catalyst content as low as 0.02 mol%. Iminopyridine ligands, as part of the catalyst and made in one step from commercially available chemicals in the case of catalyst 1, can control and invert the stereoselectivity of the polymerization. Iron complexes are suitable precatalysts for the polymerization of olefins such as ethylene to afford linear polyethylene of molar masses greater than 10 gmol . 2] Less attention has been dedicated to the iron-catalyzed polymerization of dienes such as isoprene. Polyisoprene is a naturally occurring unsaturated hydrocarbon polymer that can be refined from the latex produced by rubber trees such as Hevea brasiliensis. 5] Polymerization of isoprene can afford several isomers of polyisoprene; for example, the double bond in 1,4-polyisoprene can have either cis or trans geometry (Scheme 1). Selective polymerization is important because the identity of the isomer influences the properties of the resulting material. Natural polyisoprene can reach a cis-1,4 content exceeding 99.9% in the case of Hevea bransiliensis and a trans-1,4 content exceeding 99.9% for Gutta-percha. Natural rubber, which displays high-performance mechanical properties, is preferred over synthetic rubber in many elastomer applications, including aircraft tires and surgical gloves. As a result, more than 10 million tons of natural rubber is harvested annually from Hevea trees. Rubber trees grow only in the tropics, such as in Asia and West Africa, where they supplant food crops and are an environmental burden because of the heavy use of arsenic-based pesticides. Synthetic rubber has been introduced to replace natural rubber in less demanding applications and to reduce the extensive culturing of rubber trees. Industrial polydienes can be made by alkyllithium-based anionic polymerization. Catalysts based on titanium and, more recently, rare-earth metals such as neodymium can selectively afford high-molar-mass cis-1,4and trans-1,4polyisoprene and -polybutadiene in up to 98% yield. The molecular iron complexes we report here can provide both cis and trans isomers of polyisoprene and other 1,3dienes in greater than 99:1 selectivity, and provide new elastomer materials. Iron catalysis, if appropriately developed, could have a future impact on elastomer production because of the low cost and low environmental burden of iron compared to other transition metals. Our catalyst design was inspired by the iron bisiminopyridine complexes introduced by Gibson and Brookhart in 1998 that are used for ethylene polymerization and can also be employed for hydrosilylation reactions, as reported by Chirik et al. The iminopyridine ligands in 1 and 2 which we chose for our studies feature the redox-active behavior of the bisiminopyridines, but provide an additional available coordination site to accommodate diene coordination as opposed to alkene coordination (Scheme 1). We previScheme 1. Polymerization of isoprene using precatalysts 1 and 2. Complex 1 affords trans-1,4-polyisoprene preferentially, whereas complex 2 affords cis-1,4-polyisoprene preferentially. The 3,4-insertion motif is a minor component in both polymers (7–8% content for 1, and 15% content for 2). R= iBu for 1 and Et for 2.

Abstract: We study the hydrodynamic interaction between a sphere and an elastic surface at a nanoscale with a dynamic surface force apparatus. We show that the interplay between viscous forces and elastic deformations leads to very rich scaling properties of the force response, providing a unique signature of the surface elastic behavior. These properties are illustrated on three different examples: a thick elastomer, a thin elastomer film, and a layer of micrometric bubbles. We show that this fluid probing allows one to measure the Young's modulus of surfaces and soft thin layers at distance, without any direct solid-solid contact.

Abstract: Dielectric elastomer transducers are often subject to large tensile stretches and are susceptible to rupture. Here we carry out an experimental study of the rupture behavior of membranes of an acrylic dielectric elastomer. Pure-shear test specimens are used to measure force-displacement curves, using samples with and without pre-cracks. We find that introducing a pre-crack into a membrane drastically reduces the stretch at rupture. Furthermore, we measure the stretch at rupture and fracture energy using samples of different heights at various stretch-rates. The stretch at rupture is found to decrease with sample height, and the fracture energy is found to increase with stretch-rate.

Abstract: Dielectric elastomers with low elastic stiffness and high dielectric constant are smart materials that produce large strains (up to 300%) and belong to the group of electroactive polymers. Dielectric elastomer actuators are made from films of dielectric elastomers coated on both sides with compliant electrode material. Poly(3,4-ethylenedioxythiophene) (PEDOT), which is known as a transparent conducting polymer, has been widely used as an interfacial layer or polymer electrode in polymer electronic devices. In this study, we propose the transparent dielectric elastomer as a material of actuator driving variable-focus lens system using PEDOT as a transparent electrode. The variable-focus lens module has light transmittance up to 70% and maximum displacement up to 450. When voltage is applied to the fabricated lens module, optical focal length is changed. We anticipate our research to be a starting point for new model of variable-focus lens system. This system could find applications in portable devices, such as digital cameras, camcorder, and cell phones.

Abstract: Provided is a pneumatic tire having an inner liner layer which is formed from a laminate sheet produced by laminating a sheet comprising a thermoplastic resin or a thermoplastic resin composition comprising a blend of a thermoplastic resin and an elastomer on a rubber capable of cure-adhesion to the thermoplastic resin or the thermoplastic resin composition, whereby it becomes possible to provide the tire that does not undergo the cracking in the vicinity of a splice part of the inner liner layer after the initiation of running of the pneumatic tire and therefore has excellent durability. A pneumatic tire produced by laminating a sheet (2) which comprises a thermoplastic resin or a thermoplastic resin composition comprising a blend of a thermoplastic resin and an elastomer on a rubber (3) which is capable of cure-adhesion to the thermoplastic resin or the thermoplastic resin composition to produce a laminate sheet (1) and lap-splicing an end part of the laminate sheet (1) to form an inner liner layer (10), wherein, in the sheet (2) comprising the thermoplastic resin or the thermoplastic resin comprising the blend of the thermoplastic resin and the elastomer to be used, the tip of the end part is sharpened.

Abstract: Lightly cross-linked natural rubber (NR, cis-1,4-polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain-induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain-stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature T(trig) (σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal-stabilized SMP after programming.

Abstract: Magnetorheological elastomers, MREs, based on elastic organic matrices displaying anisotropic magnetoresistance and piezoresistivity at room temperature were prepared and characterized. These materials are dispersions of superparamagnetic magnetite forming cores of aggregated nanoparticles inside silver microparticles that are dispersed in an elastomeric polymer (poly(dimethylsiloxane), PDMS), curing the polymer in the presence of a uniform magnetic field. In this way, the elastic material becomes structured as the application of the field induces the formation of filaments of silver-covered inorganic material agglomerates (needles) aligned in the direction of the field (parallel to the field). Because the magnetic particles are covered with silver, the MREs are not only magnetic but also electrical conductors. The structuration induces elastic, magnetic, and electrical anisotropic properties. For example, with a low concentration of particles in the elastic matrix (5% w/w) it is possible to obtain resist...

Abstract: Dielectric elastomers are emerging electroactive materials used in high performance applications such as robots, artificial muscles and energy harvesting. The development of such applications requires the use of accurate, predictive, reliable models which take into account the dielectric constant (permittivity) of these materials. This dielectric constant is not clearly defined for such applications and depends on many parameters. This leads to values dispersed in the literature for the same electroactive polymer. This paper shows that the nature of the compliant electrodes can influence this dielectric constant significantly. However, the reduction generally observed in this permittivity according to the stretching of elastomer cannot be imputed to the nature of these electrodes, and rather confirms an effect of the volume of the elastomer. This tends to prove that the influence of the compliant electrode is located at the electrode–elastomer interfaces. In addition, the nature of the metallic particles embedded in the electrode grease seems not to influence the value of the dielectric constant. Lastly, we propose analytic laws to describe changes of the dielectric constant as a function of the temperature and the deformation of the material. This makes it possible to define new limits of operation for these polymers for actuators and energy harvesting applications.