Highly stretchable dielectric elastomer composites containing high volume fractions of silver nanoparticles

The dielectric permittivity (epsilon') of a polymeric material can be significantly increased when blended with conductive fillers at concentrations approaching the percolation threshold. However, reproducible synthesis of such composites is after decades of research still a major challenge and a bottleneck for their application. Difficulties arise in controlling the size and shape of the filler as well as in its homogenous distribution within the composite. These parameters strongly affect the dielectric as well as mechanical properties of the composite. While a substantial amount of literature deals with the influence of conductive fillers on the dielectric properties of composites, little is known about their mechanical properties. It is therefore still an important goal to synthesize materials with simultaneously high 30 and good mechanical properties. Here, we report the synthesis of dielectric elastomers that combine key properties such as high flexibility and stretchability, high thermal stability, increased epsilon', low dielectric loss and conductivity. Such materials were prepared by solution processing using quasi-spherical silver nanoparticles (AgNPs) of a defined size in a polydimethylsiloxane matrix (M-w - 692 kDa). To prevent percolation, the AgNPs were coated with a thin silica shell (