Large area and flexible micro-porous piezoelectric materials for soft robotic skin

The need for flexible, highly sensitive tactile sensors that can fit onto curved surfaces is driving the conformable sensor materials research in the field of human machine interactions. Here we report a new type of compliant piezoelectric active composite, a micro-porous polyurethane-PZT material, capable of generating a voltage output upon touch. The composites are synthesized with the aim of maximizing the piezoelectric sensitivity of particulate composite sensor materials. The goal is to reduce the dielectric constant of the polymer matrix and improve flexibility of conventional bulk piezo-composites, consisting of ceramic particles in a dense polymeric matrix, by adding a third (gaseous) phase to the system in the form of uniformly sized pores. The presence of the gaseous component in the polymer matrix in the form of well-distributed spherical inclusions effectively decreases the polymer dielectric permittivity, which increases the piezoelectric voltage sensitivity (g(33)) of the composite sensors significantly. The unique combination of dielectrophoretic structuring of PZT particles and the addition of a gaseous phase to the polymer resin results in the highest performance of the particulate composite sensors reported in the literature so far. The newly developed micro-porous composites show g(33) value of 165 mV m/N that is twice that of the structured PZT-bulk PU composites (80 mV m/N) and more than five times the g(33) value of bulk PZT ceramics (24-28 mV m/N). The capability of the flexible freestanding sensors for application in touch sensing devices for soft robotics is demonstrated. (C) 2017 Elsevier B.V. All rights reserved.