Underwater can be self-healing thermoplastic elastomer boost the development of flexible electronics
In recent years, the rapid development of flexible electronic devices, which are widely used in medical diagnosis, monitoring areas and flexible robots. However, the disadvantage of this device is that, due to its soft nature, they are very sensitive to mechanical damage. If the self-healing capabilities can be incorporated into the existing flexible devices, so that it can be self-recovery after external damage, will greatly improve the life of the device, reliability and durability. For most flexible electronic devices is concerned, we very much hope that it can be used underwater or waterproof, because the device during use, inevitably encounter various humidity environments, such as human sweat or natural rainwater. Unless the material is not sensitive to water, or structural damage these devices will occur in the face of the water, thereby affecting related functions. Therefore, we need to develop an underwater can be used for flexible electronic devices under real scene self-repairing material. In the early stages of the field, all reported There are two kinds of self-healing material underwater: 1) containing a boronic ester or boronic acid derivative of boron-oxygen bond octyl; 2) naturally occurring o hydroquinone group. However, they have limitations. Boronic acid derivative severe hydrolysis will occur, very unstable in water. Catechol group is very sensitive to pH. Recently, many researchers have reported an underwater self-healing elastomer, but there are self-healing low efficiency and poor mechanical properties insufficient, can not really be used underwater flexible electronic devices. Therefore, the current needs in the art can be summarized as: 1) the development of high strength, efficiently underwater repair material; 2) in-depth study of such materials for complex underwater electronic systems. 
Based on these issues, Israel Institute of Technology Professor Hossam Haick Task Force developed A new underwater self-healing thermoplastic elastomer. They hydroxyl-terminated polybutadiene (of HTPB) as raw materials, isophorone diisocyanate (IPDI), and 4-aminophenyl disulfide (the APDS) Two major reactions are synthesized a novel polymeric was PBPUU, related to the manufacturing process shown in Fig. Wherein, HTPB section provides low temperature flexibility and excellent water resistance, APDS component provides dynamic disulfide bonds and hydrogen bonds. Based on covalent bonds (disulfide) and non-covalent bondsPresence and high flexibility of the polymer (hydrogen) two integrated self-healing mechanism makes it a very effective self-repairing material.
On the self-healing PBPUU tested in different aqueous environment, including water, sea water, acidic solutions ( pH = 3) and an alkaline solution (pH = 11). The elastomer solution in different environments self-repairing efficiency reached more than 80% (24 h) , such good self-repairing ability from underwater PBPUU highly hydrophobic repeating units (butadiene diene). Mechanical test results show that the polymer has have good mechanical properties, elongation up to 1100%, a maximum tensile strength of 6.5 MPa (FIG. 2). Self-healing properties and mechanical properties
In order to influence the behavior of the polymer in water environment study design, simulation of molecular dynamics (image 3). The PBPUU OF PPGPUU compared with two polymers wherein the repeating units of the butadiene became PPGPUU glycol. Found, there PBPUU hard and soft phases were separated, aqueous phase only interact with the molecules PBPUU hard and hardly diffuses into the water phase PBPUU soft. In contrast, for PPGPUU, water molecules across the soft polymer phase region, the destruction of the intermolecular forces and resulting in a high swelling rate. These results were verified by swelling experiments.
Finally, the authors show that the skin material is applied underwater electronic sensors and strain (Fig 4, 5). We believe that with the development of underwater self-healing materials, the application will provide a broader prospects in the future flexible electronics.
Original link : https: //onlinelibrary.wiHappy .com / do i / 10.1002 / A unilateral .201910196
