Super soft silicone elastomers with high dielectric permittivity

Abstract

Dielectric elastomers (DEs) have many favourable properties. The obstacle of high driving voltages, however, limits the commercial viability of the technology at present. Driving voltage can be lowered by decreasing the Young's modulus and increasing the dielectric permittivity of silicone elastomers. A decrease in Young's modulus, however, is often accompanied by the loss of mechanical stability and thereby the lifetime of the DE. New soft elastomer matrices with high dielectric permittivity and low Young's modulus, with no loss of mechanical stability, were prepared by two different approaches using chloropropyl-functional silicone polymers. The first approach was based on synthesised chloropropyl-functional copolymers that were cross-linkable and thereby formed the basis of new silicone networks with high dielectric permittivity (e.g. a 43% increase). These networks were soft without compromising other important properties of DEs such as viscous and dielectric losses as well as electrical breakdown strength. The second approach was based on the addition of commercially available chloropropyl-functional silicone oil to commercial LSR silicone elastomer. Two-fold increase in permittivity was obtained by this method and the silicone oil decreased the Young's modulus significantly. The viscous losses, however, also increased with increasing content of silicone oil. Cross-linkable chloropropyl-functional copolymers offer a new silicone elastomer matrix that could form the basis of dielectric elastomers of the future, whereas the chloropropyl silicone oil approach is an easy tool for improvement of the properties of existing commercial silicone elastomers.

The Current State of Silicone-Based Dielectric Elastomer Transducers

“…In order to overcome the increased dielectric losses that usually arise when attempting to increase dielectric permittivity, Madsen et al used a chloropropyl‐functional silicone oil, namely LMS‐152 from Gelest Inc., as an additive to the commercial silicone elastomer LR3043/50, supplied by Wacker Chemie. At a content of up to 30 phr LMS‐152 dielectric permittivity increased to ε' = 4.4 while the dielectric loss tangent decreased.…”

“…Recently, a very promising and much simpler silicone elastomer system, based on chloropropyl‐functional siloxane copolymers, has been developed by Madsen et al These elastomers possessed a low Young's modulus (0.4 – 1 MPa, 75–90% lower than the utilised silicone reference) and high dielectric permittivity ( ε' = 4.7 at 1 MHz). Dielectric losses, remarkably, remained as low as those of pure PDMS elastomers, and high dielectric breakdown strengths were obtained (94.4 V μm −1 ), thus increasing the maximum achievable actuation, ε' / Y × E B 2 , significantly (between seven and ten times).…”

Mechanical and Electrical Ageing Effects on the Long‐Term Stretching of Silicone Dielectric Elastomers with Soft Fillers

“…Since it is also desired to increase dielectric permittivity, functional silicone oils can be used as an alternative to hard fillers such as TiO 2 , which has previously been shown to introduce ageing effects in silicone elastomers . Functional silicone oils will soften elastomer while at the same time increasing permittivity, and thereby actuator performance will be increased significantly through a synergistic effect . Such additives, however, may induce significant ageing effects due to phase separation and/or migration of the free species.…”

“…This ultimately created a material with superior elasticity and without the waxy consistency of traditional high‐molecular weight silicones. Finally, softened DEs have been prepared through the use of permittivity‐enhancing blends, where polymers such as poly(3‐hexylthiophene), polyethylene glycol, a cyanopropyl‐functional copolymer, and chloropropyl‐functional silicone oil have been used.…”

Incorporation of liquid fillers into silicone foams to enhance the electro-mechanical properties

“…The Foam-cloil shows the smallest Y of 31 kPa, as the oil self-lubricates resulting in the softest network. The presence of Cl-silicone oil swells and softens the Foamcloil and decreases the Y by almost 3 times compared to the Foam-ori [31]. The glycerol is insoluble in silicone and it does not soften the foam, therefore, Foam-gly has a higher stiffness (Y ≈ 82 kPa).…”