Extremely Stretchable and Tough Piezoelectric Gels for Artificial Electronic Skin

Abstract

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 (dabcoHReO4, 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 (d33 ≈ 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 µW cm−2. This work is expected to motivate new design principles for fabricating piezoelectric materials with excellent mechanical and piezoelectric properties for various applications.

Smart Core‐Shell Nanostructures for Force, Humidity, and Temperature Multi‐Stimuli Responsiveness

“…[5][6][7][8] An efficient e-skin design requires a combination of functional materials with suitable mechanical and electrical properties, [9] in addition to the micro/nanoscale control of the layer's thickness and dimensions, which is optimized by the choice of suitable fabrication techniques.For pressure and force detection, the most common methods exploit piezoelectric, piezoresistive, or capacitive sensing. [10][11][12][13] Bao's group investigated an e-skin design based on flexible pressure-sensitive organic thinfilm transistors deploying a force-sensitive gate dielectric capacitance. The sensor has a maximum sensitivity of 8.4 kPa −1 and a fast response time of 10 ms.…”

“…For pressure and force detection, the most common methods exploit piezoelectric, piezoresistive, or capacitive sensing. [10][11][12][13] Bao's group investigated an e-skin design based on flexible pressure-sensitive organic thinfilm transistors deploying a force-sensitive gate dielectric capacitance. The sensor has a maximum sensitivity of 8.4 kPa −1 and a fast response time of 10 ms.…”

Perspectives on recent advancements in energy harvesting, sensing and bio-medical applications of piezoelectric gels

“…For instance, the PUU-DH PiezoGel showed several prototype applications of LED lighting, object deformation detection and human motion detection demonstrating the potential uses in self-powered, wearable and artificial e-skin applications. 356 It is interesting to note that in another study, a piezoelectric hydrogel derived from ferroelectric PAN-PVDF revealed excellent piezoelectric coefficient (d 33 , 30 pC N À1 ), skin-like Young's modulus values (1.33-4.24 MPa), good stretchability (90-175%) and high toughness (1.23 MJ m À2 ), indicating it as a promising material for artificial e-skin applications. 266 Moreover, the PiezoGel-based pressure sensor was shown to be capable of detecting physiological signals such as gestures, pulses, and spoken words.…”

A Review on Epidermal Nanogenerators: Recent Progress of the Future Self‐Powered Skins

“…Stretchable and/or shape adaptable 41 [53,79,126,130,158, Ultrathin d) 5 [183,190,205,210,213] Transparent 9 [130,158,182,187,194,196,203,206,213] Sweat permeable 1 [213] Wireless connected 5 [208,[214][215][216][217] Low-cost 11 [179,183,188,190,191,198,199,204,211,214,218] Facile manufacturing 6 [179,183,184,188,199,214] Biocompatible 4 [53,79,190,213] Metal-free 1 [219] Humidity resistive 2 [181,220] Self-healable 5…”