Elastomer | EPFL Graph Search

An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus (E) and high failure strain compared with other materials. The term, a portmanteau of elastic polymer, is often used interchangeably with rubber, although the latter is preferred when referring to vulcanisates. Each of the monomers which link to form the polymer is usually a compound of several elements among carbon, hydrogen, oxygen and silicon. Elastomers are amorphous polymers maintained above their glass transition temperature, so that considerable molecular reconformation is feasible without breaking of covalent bonds. At ambient temperatures, such rubbers are thus relatively compliant (E ≈ 3 MPa) and deformable. Their primary uses are for seals, adhesives and molded flexible parts. Rubber-like solids with elastic properties are called elastomers. Polymer chains are held together in these materials by relatively weak inter

Design of High Permittivity Polysiloxane Elastomers for Dielectric Elastomer Transducers

Philip Horst Caspari

Dielectric elastomer transducers consist of a dielectric elastomer between two compliant electrodes. When the elastic capacitor is electrically charged, the dielectric elastomer elongates until a balance of elastic and electrostatic force is reached. Electrical energy is converted into mechanical work. Contrary, in the generator mode, the capacitor is stretched by an outside mechanical force. The mechanical work is converted into electrical energy due to the change of capacitance. The need of a high voltage power supply is the main obstacle for the elastomer transducer technology in various applications. Siloxane elastomers are the most frequently tested elastomers with excellent mechanical stability, processability and electrically insulating properties. It is well-known that an increase in permittivity of the silicone elastomer would allow a reduction of the driving voltage of the elastic transducer. Hence, manifold research activities have been initiated to enhance the permittivity of siloxane elastomers. In the present work, siloxane elastomers were developed that combined increased permittivity with high mechanical stability and cost-efficient processability of the siloxane materials. The synthesis of polar thiols as the first step of siloxane functionalization was studied. Serious challenges in the synthesis of polar groups that can be integrated by thiol-ene addition as side group of polysiloxanes were found. Therefore, commercially available alkylthiols were selected for the functionalization of siloxane due to their chemical stability. The alkylthiols were grafted onto the polysiloxane by thiol-ene addition and subsequently cross-linked in the well-established organotin-catalyzed condensation reaction. The impact of different types of cross-linker on the electro-mechanical properties of the polar siloxane elastomers was analyzed. A significant improvement in the performance of actuator test devices was demonstrated. In addition, the electromechanical stability of the polar siloxane elastomer was illustrated by 50.000 actuation cycles. However, solvent had to be used in the production process of the siloxane elastomers and the cross-linking reaction time was about two days. Apart from their application in thin film actuators, these polar siloxane elastomers were studied with respect to their performance in dielectric elastomer generators together with siloxane composites. Nanospring carbon nanotubes were blended as high permittivity fillers in siloxanes subsequent to cross-linking. Indeed, improved performances of the high permittivity silicone elastomers were found and a deeper understanding for the design of dielectric elastomers for generator applications was gained. The most significant result of this work was the development of polar siloxane elastomers that could be processed into thin film elastomers without any solvent within a few minutes. Two different synthetic approaches were developed based on low viscosity mixtures of cross-linkable oligo(ethylthioethyl)(methyl)siloxanes and multifunctional thiol cross-linkers. The cross-linking reaction was selectively initiated by UV-induced radical formation. These siloxane elastomers possessed an increased permittivity and showed a high electromechanical stability.

EPFL2019

Automated test setup to quantify the lifetime of dielectric elastomer actuators under a wide range of operating conditions

Fabio Beco Albuquerque, Djen Timo Kühnel, Valentin Colin Py, Herbert Shea

We present an automated test setup for the systematic performance and lifetime evaluation of dielectric elastomer actuators (DEAs). This setup, called the MAPLE setup, performs accelerated aging tests and allows quantifying how material choice, fabrication methods, voltage waveform, and environmental conditions influence DEA lifetime, an important step for commercial use of DEAs. The setup continuously monitors strain and electrode resistance of multiple DEAs under a wide range of environmental conditions (up to 85 degrees C and 85% relative humidity), with automatic breakdown detection to record device lifetime. To illustrate a use case, we investigate the lifetime of DEAs made of two different elastomer materials, comparing fixed polarity (FP) vs. periodically reversing the polarity of the actuation voltage. For DEAs made from a slide-ring material, lifetime improvements around 10x were observed at alternating polarity compared to FP. For DEAs made from silicone rubber, no improvement in lifetime was observed. This indicates that different degradation mechanisms are causing failure in the two materials.

IOP PUBLISHING LTD2021

Poleable Nanoparticles as Fillers Towards Non-linear Optically Active Actuators

Yee Song Ko

A new type of poleable dielectric elastomer is introduced herein. The elastomer contains polymer nanoparticles with frozen molecular dipoles, which can be oriented at elevated temperatures in an electric field via poling. The aim is to provide a soft material with high, tunable optical properties suitable for actuator and flexible electronics applications. To that end poleable polymeric nanoparticles with high dipole concentrations and glass transition temperatures well above room temperature will be needed to be used as filler in an elastomer matrix. The synthesis and characterization of such particles is presented in this manuscript. Polyhydroxyethyl methacrylate (PHEMA) nanoparticles were synthesized using miniemulsion polymerization. The particles were loaded with 4-[ ethyl (2-hydroxyethyl) amino]-4-nitrobenzene, usually called Disperse Red 1 (DR1), which has a large dipole moment (mu = 7.5 - 9.5 D). (1) The maximum dipole loadings is limited by the solubility of the dipole in the monomer solutions prior to polymerization. All samples show a glass transition temperature around 95 degrees C. Secondary electron microscopy (SEM) revealed spherical particles, the size of which was confirmed by dynamic light scattering (DLS) measurements. A composite was prepared by dispersing the particles in polydimethyl siloxane (PDMS).

Spie-Int Soc Optical Engineering2015

Design of High Permittivity Polysiloxane Elastomers for Dielectric Elastomer Transducers

Philip Horst Caspari

EPFL2019