Conductive emulsions with selective filler distribution as volume exclusion strategy in electrofluids

Abstract

A classical approach to reduce the percolation threshold in conductive polymer composites is the so-called volume exclusion. While this method proved to lower the filler concentration required to achieve electrical conductivity in solid composites, it remains unexplored for liquid conductive composites such as electrofluids (EFs). We propose the combination of emulsions and conductive particles to create EFs with reduced filler content. Conductive emulsions were prepared based on two immiscible liquids, glycerol and polydimethylsiloxane (PDMS), and carbon black (CB) as the conductive filler. The structural characterization of stable emulsions revealed a selective distribution of CB in the PDMS phase (continuous phase), around glycerol droplets (dispersed phase). This configuration led to a decrease in percolation threshold proving the viability of volume exclusion as strategy in EFs. The combination of the CB network and the glycerol droplets resulted in unpredictable mechanoelectrical properties such as a reduced stiffness scaling compared to CB-EFs in the pure solvents and the reduction of a strain thickening behavior with increased filler concentration. We evaluated the role of the CB in the emulsion formation and its impact on the droplet size and size distribution and concluded that this effect must be synergetic with the creation of a stress-carrying filler network that absorbs the elastic energy from the droplet deformation at large strains.