Characterizing the combined effect of electrostatics and polymer adhesion for elastomer-based electroadhesives
Chen, Simpson Abraham
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This dissertation presents work done in the fabrication and characterization of polymer-based electroadhesives to understand the underlying mechanisms of electroadhesion with the inclusion of soft polymers as the functional surface material. Electrostatic models for parallel plate and interdigitated electrodes provide insight into the effect of design parameters on electric fields. However, little work has been done to model how electrostatic force affect adhesion in soft electroadhesives while accounting for their mechanical and material properties. To this end, a basic friction model is presented to describe the critical shear force for a single electrode electroadhesive. The effect of voltage, contact area, dielectric thickness, and bulk thickness on shear adhesion is explored. It was shown that within a range of design parameters the basic friction model could accurately predict the critical shear force and with stiff dielectric layers higher compliance improved adhesion. However, improved models are required to cover behavior over a larger parameter space. To move beyond friction-based modeling, the combined effect of polymer adhesion and electrostatic force on conductive polymer layers is explored through performing JKR tack tests. Tack tests can measure the intrinsic adhesive property of a polymer, called the critical energy release rate. By performing JKR tack tests with two different tack systems, a rigid probe contacting a soft elastic surface and a soft probe contacting a rigid surface, it was shown that the combination of the two adhesion mechanisms can be described as a superposition of the critical energy release rate of the polymer and electrostatic force. Using these findings, a design framework is developed to combine gecko adhesives with electrostatics to increase the controllable adhesion range. Textured electroadhesives with arrays of spherical bumps were fabricated and showed an increase in adhesion up to 20x. The textured electroadhesives were also mounted onto 3D printed mounts to pick up various objects weighing from 2g to 60g. The work presented here provides a theoretical and design framework for future soft electroadhesives to build upon for applications from climbing robots to pick and place manufacturing.