Extremely Stretchable and Tough Piezoelectric Gels for Artificial Electronic Skin

Piezoelectric sensors and energy harvesters have received considerable interest due to their self-powered capability and potential applications in various electronic devices. However, it is still a challenge to fabricate stretchable piezoelectric devices because piezoelectrics mainly consists of stiff crystalline structures. Here, extremely stretchable and tough piezoelectric gels are reported, which are prepared simply by swelling poly(ethylene glycol) (PEG)-based poly(urethane-urea) (PUU) gels with aqueous solution of molecular ferroelectrics. The hydrogen interactions between the PEG segments in the gels and the molecular ferroelectrics (dabcoHReO(4), DH) enable well dispersion and crystallization of DH in the PEG segments. The resulted PUU/DH composite piezoelectric gels exhibit unique tensile mechanical properties, including superior strain (>1000%), high breaking strength (>10 MPa), modulus (>2 MPa), and toughness (>57 MJ cm(-3)). The extremely stretchable and tough piezoelectric gels show excellent piezoelectric properties (d(33) approximate to 62 pC N-1 for films with a 10 wt% of DH and light transparency (>90%), and can quantitatively detect different mechanical deformations. Additionally, the energy generators can harvest mechanical energy with a power density of 1.7 mu W cm(-2). This work is expected to motivate new design principles for fabricating piezoelectric materials with excellent mechanical and piezoelectric properties for various applications.