(639b) Multi-Material Composites Including Liquid Metal for Improved Capacitive Sensing

Capacitive pressure sensing performance is directly related to two key material properties: stiffness and dielectric permittivity. Low stiffness, as indicated by bulk modulus, is optimal for sensitivity while high stiffness is optimal for a wide sensing range. Unfortunately, this illustrates the difficulty in obtaining pressure sensors that have both a wide force bandwidth and can detect small changes in force and pressure. Dielectric permittivity is the other material property that can be tuned in order to move towards a high sensitivity, wide pressure range material. For composites, dielectric permittivity is increased by increasing the loading of conductive or capacitive material, which is almost exclusively a rigid filler. Thus, by increasing the dielectric permittivity of a material, one also generally increases its stiffness and decreases sensitivity. In this work, a PDMS composite of multiple electronically responsive materials including rigid materials and the liquid, eutectic metal gallium-indium-tin (galinstan) are blended to create soft and stretchable dielectric materials, which show unique sensitivity and force profiles due to the presence of the deformable, conductive galinstan. We look at the modulus, permittivity, filler-interaction, and pressure/capacitance profiles of a range of filler compositions and loadings to determine (1) how the liquid metal changes the electrical and mechanical behavior of the material, (2) how conductive and capacitive fillers differ in their impact on sensitivity, and (3) determine paths forward to create a capacitive sensor material that can achieve both a wide pressure sensing range and high force sensitivity.