Investigation on dielectric properties of solid silicone rubber particulate composites

Abstract

Dielectric elastomers belong to the class of electroactive polymers that respond to electrical stimulus by undergoing change in shape. These materials also produce electrical signal on being deformed mechanically. The objective of the present study is to investigate the solid silicone rubber composites as candidate materials for use as dielectric elastomers. Solid silicone rubber along with barium titanate as dielectric and ketjenblack as conductive fillers is processed through high temperature compression moulding to obtain dielectric-dielectric, conductive-dielectric and conductivedielectric-dielectric composites. Property-processing relationships are investigated for these composites by studying the influences of various factors such as type and amount of fillers, amount of curing agent, mixing time and curing temperature using Taguchi design of experiments. The properties investigated include physical, mechanical, dielectric and electromechanical. Various dielectric mixing rules have been evaluated for the dielectric filler composites. Dielectric spectroscopy and SEM characterization have also been carried out on these composites in order to study filler-matrix interactions. Results show that the processing parameters along with fillers have influence on physical, mechanical, dielectric and electromechanical properties of the composites. Conductive fillers have a prominent influence on permittivity of the composites as compared to dielectric fillers. However, they are more reinforcing than dielectric fillers. The investigations reveal improved dielectric permittivity and electromechanical sensitivity of 390% and 100% respectively. Piezoresistive and piezo capacitive sensitivities of 3.7E-3 kPa-1 and 3.9E-3 kPa-1 respectively were achieved in the 0-20 kPa range of pressure for the composites. The processing method adopted ensures uniform distribution and wetting of the fillers in the solid silicone rubber matrix as confirmed through SEM characterisation. Thus, solid silicone rubber composites can be used as promising materials for use as dielectric elastomers.