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

Silicone foams with and without liquid fillers (silicone oils of various types and glycerol, respectively) are synthesized and analyzed to be used as dielectric layers in capacitive sensors. A simple fabrication technique involving only four components i.e. Sylgard 184, glycerol, sodium hydroxide and ethanol is used to make these silicone foams after which they are filled with silicone oil or glycerol by soaking the foam in respective liquid. Mechanical and dielectric properties of the foams are examined. The oil reinforces the foam's dielectric properties, softens the foam and improves its capacitive response, making it a very good dielectric material for fabricating capacitive pressure sensors. Compared to dry silicone foams, foams filled with - and swollen by - chloropropyl-functional silicone oil, show a low Young's modulus (31 kPa), a high and stable relative dielectric permittivity of around 5, and a high capacitive response of 132% for an applied pressure of 12 kPa. The presence of oil stabilizes the soft foam and ensures that it does not buckle under high pressure.