Sunlight‐Triggerable Transient Energy Harvester and Sensors Based on Triboelectric Nanogenerator Using Acid‐Sensitive Poly(phthalaldehyde)

Abstract

operation. [5] They have found potential applications as medical diagnostic and therapeutic devices that can resorb into the body, environmental sensors that do not require recovery after data collection, and consumer devices that can be easily disposed without hazards. [6] The potential feature of disappearance with minimal or non-traceable remains also enables transient electronics to find opportunities in privacy or security applications where stealth is required or reverse engineering needs to be avoided. The transience property is largely attributed to the triggerable degradation of device substrates and encapsulation, which are typically made of a group of materials called transient polymers. Depending on constituting material, the transience can be achieved either through material dissolution or depolymerization. Pioneering efforts on transient electronics focused on solution dissolution of polymer matrix. Bioresorbable polymers such as silk, polycaprolactone, poly(glycolic acid), and poly(L-lactide-co-glycolide), were used as substrates, [7][8][9] and biocompatible, implantable devices such as transistor, [1] ring oscillators, [10] and energy harvesters, [11] have been demonstrated. The lifetime of such devices is controlled by the dissolution rate of the materials in the surrounding aqueous solution, making them unsuitable for non-biological applications. Transient electronics that disintegrate via material dissolution or depolymerization under certain stimuli have great potential in biomedical and military applications. The triboelectric nanogenerator (TENG), an emerging mechanical energy harvesting technology with great flexibility in material choices, is promising in offering transient power sources. Previously reported transient energy harvesters using biodegradable polymers require solutionbased degradation and have limited applications in non-biological scenarios. A short time span, sunlight-triggered degradable TENG is developed. The main substrate includes an acid-sensitive poly(phthalaldehyde) (PPHA), a photoacid generator (PAG), and a photosensitizer (PS). Through photoinduced electron transfer, the ultraviolet radiation absorbed by the PS istransferred to the PAG to generate photoacids that trigger the depolymerization of PPHA. Transient TENG-based mechanical energy harvesters and touch/acoustic sensors are successfully demonstrated by embedding silver nanowires onto the PPHA-based films. The fabricated devices degrade rapidly under winter sunlight. The degradation rate can be further tuned via changing the ratio of photosensitive agents. This work not only broadens the applicability of TENG as transient power sources and sensors, but also extends the use of transient functional polymers toward advanced energy and sensing applications.

A Review of Bioresorbable Implantable Medical Devices: Materials, Fabrication, and Implementation

“…[157] Recent work demonstrated sunlight-triggered triboelectric nanogenerators (TENG). [164] In this work, an acid-sensitive poly(phthalaldehyde) (PPHA) substrate was combined with a photosensitive package consisting of PAG and a photosensitizer (PS). The dissolution rate of such polymers can also be modified by adjusting the ratio of photosensitive agents.…”

Flexible Cyclic‐Poly(phthalaldehyde)/Poly(ε‐caprolactone) Blend Fibers with Fast Daylight‐Triggered Transience

“…[ 16,19,28,32 ] More work on the accelerated transience of cPPHA‐based plastics is still needed, especially in the case of new electronic devices. [ 26,27,33 ] Thus, the need for new approaches to process cPPHA, having advanced performance properties, is a technological challenge for the near future.…”

“…This result for outdoor transience by the 50/50 cPPHA/PCL fiber bundles, under realistic daytime conditions, were significantly faster than previously reported for cPPHA‐based products. Those products which were commonly tested against UV radiation using lasers at various wavelengths [ 27,28,33 ] (see Figure S1, Supporting Information). The opacity of films adversely affects photo‐induced transience by transmission.…”

Electromagnetic Pulse Powered by a Triboelectric Nanogenerator with Applications in Accurate Self‐Powered Sensing and Security

“…Security devices based on transient electronics have previously been developed which can disappear by physical or chemical destruction through dissolution in solvents or via vaporization, causing removal of sensitive data. [ 25–28 ] These devices have shown potential in implantable devices, as the electronics could be reabsorbed in the body. [ 29,30 ] However, a primary challenge of utilizing this method is that it would still require solvents or ultraviolet light to cause dissolution.…”

“…This can be seen in previous reports, as the electronic devices are still operating for an extended period even when the devices are placed in the solvent. [ 28,31 ] Also, with this method, users could only completely erase sensitive information, but could not change sensitive information. Thus, to address these issues, other researchers have turned to electrical fuses or antifuses powered by Joule heating or nano‐electromechanical switches.…”