The effect of organo-clay on the dielectric properties of silicone rubber

Abstract

Dielectric elastomers are highly deformable and fast response smart materials capable ofactuation under electric fields. Among commercially available dielectric elastomers, siliconerubber can be compounded with different fillers in order to modify its electrical andmechanical properties. To study the effect of organically modified montmorillonite(OMMT) on the dielectric properties of silicone rubber, OMMT was added to this rubberat two levels, 2% and 5%, using two methods, low-shear and high-shear mixing. Compositeswere characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), andatomic force microscopy (AFM). The XRD patterns showed different crystallitestructures for silicate platelets in the rubber matrix as a result of the two differentmixing methods. In low-shear mixing, the ordered crystallite structure of theclay remains almost unchanged, whereas in high-shear mixing it loses its orderedstructure, leading to the disappearance of the diffraction peaks. SEM and AFMmicrographs depicted better dispersion and more uniform distribution of the organo-clayunder high-shear mixing compared to those obtained by low-shear mixing. Thetensile properties also confirmed the different degree of dispersion of the nano-clayresulting from the two different methods of mixing. The dielectric properties of thecomposites were measured under AC electric fields, and the results were comparedwith reference silicone rubbers with no OMMT. It was shown that the order oforgano-clay layers in the less dispersed structure of the clay imparts an additional ionicpolarization and higher dielectric permittivity compared to the case where the claylayers are more dispersed and lost their order. The storage and loss dielectricconstants of base silicone rubber increase when it is compounded with OMMT.