Polydimethylsiloxane | EPFL Graph Search

Polydimethylsiloxane (PDMS), also known as dimethylpolysiloxane or dimethicone, is a silicone polymer with a wide variety of uses, from cosmetics to industrial lubrication. It is particularly known for its unusual rheological (or flow) properties. PDMS is optically clear and, in general, inert, non-toxic, and non-flammable. It is one of several types of silicone oil (polymerized siloxane). Its applications range from contact lenses and medical devices to elastomers; it is also present in shampoos (as it makes hair shiny and slippery), food (antifoaming agent), caulk, lubricants and heat-resistant tiles. Structure The chemical formula of PDMS is , where n is the number of repeating monomer units. Industrial synthesis can begin from dimethyldichlorosilane and water by the following net reaction: : The polymerization reaction evolves hydrochloric acid. For medical and domestic applications, a process was developed in which the chlorine atoms in the silane precursor were replac

Nitric oxide release from Polydimethylsiloxane-based Polyurethanes

Evelyne Nguyen

In bypass graft surgery, surgeons have turned to synthetic materials such as polyethylene terephthalate (Dacron) and expanded polytetrafluoroethylene (ePTFE) when lacking sufficient and suitable arteries or veins for the procedure. However, due to their low patency in small-caliber bypass surgery (

2009

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

High Permittivity Silicones for Dielectric Elastomer Actuators

Simon Johannes Dünki

Many technical advances of modern society sprout from the creation of specially customized polymer materials exhibiting unique combinations of properties uncharted so far. Amid this plurality of highly versatile materials, the class of electroactive polymers (EAPs) bears the special ability to undergo large shape changes when exposed to electrical stimulation. Such materials offer new perspectives in automation, robotics and medicine. Especially the dielectric elastomer actuators (DEA) technology is considered as highly promising among EAPs due to the simple working principle and actuation characteristics similar to mammalian muscles. Despite great research efforts and remarkable progress in regard to materials and devices, the commercial breakthrough of the DEA technology is still outstanding. A major obstacle for their application is the high driving voltage needed to obtain a reasonable actuation. The development of tailored elastomers that overcome this deficiency is therefore a main research focus in academia and industry. The exceptional elastic and dielectric characteristics of silicones nominate them as an ideal vantage point to start this endeavor. Their low permittivity inherently decreases the actuation performance and should therefore be optimized with all other properties remaining unaffected. In the present work, dipoles were covalently attached to a siloxane backbone in order to increase the permittivity thereof and achieve a material with an enhanced actuation performance at low driving voltages for DEAs. The introduction of the polar groups to the polymer side chains was carried out via thiol-ene chemistry, which enabled a quantitative functionalization of the polymer backbone. Three different polar groups, nitrile, thioether and sulfones, were investigated and the corresponding functionalized polysiloxanes were prepared and characterized. Thorough dielectric, mechanical and electromechanical investigations were conducted on polysiloxane based elastomers with different content of nitrile groups. In addition, first results were obtained with thioethers and sulfones which are also promising candidates to enhance the permittivity of polysiloxanes. Most of the synthesized polysiloxanes show glass transition temperatures well below room temperature, an important prerequisite to ensure elastic properties. Polysiloxanes that carry a butylthioether moiety at every repeat unit doubled the permittivity of the elastomer. With the same amount of the nitrile or sulfone dipoles, a six respectively eight times higher permittivity as compared to regular siloxane is achieved. However, with enhanced dipole content also an increase of the electrical conductivity of the polymer was observed. A simple one-step process to prepare cross-linked polar silicone films was developed using UV light triggered thiol-ene addition. A strong correlation between the dipole content in the material and the resulting actuation strain was found. Finally, a polar silicone elastomer was prepared that showed up to 20.5% lateral strain under a field as low as 10.8 V/um. Compared to commercial silicone this corresponds to an effective voltage reduction by about 70%. Processing such materials in films the thickness of which is below 10 um would result in an actuator that can be driven below 100 V.