Simultaneously achieving superior foldability, mechanical strength and toughness for transparent healable polysiloxane films through building hierarchical crosslinked networks and dual dynamic bonds

The rapid development of flexible transparent electronic devices puts forward more requirements for substrate materials, not only including high transparency, but also possessing good self-healing ability, high mechanical strength and toughness. Herein, a urea-containing chain-extended polydimethylsiloxane (LPx) was first designed and synthesized to construct dynamic physical crosslinks induced by hydrogen bonds. Subsequently, multi-amino terminated hyperbranched polysiloxane (HPSi) was selected as the permanent chemical crosslinking point and connected with LPx through isocyanate with controlled exchangeable aliphatic disulfide (SS-NCO). Consequently, a series of LPx-SS-HP films with hierarchical crosslinked networks and dual dynamic bonds are developed. The chain-extension degree of LPx has been proved to play a key role in adjusting the mechanical, thermal and self-healing properties. Among the serial films, LP2-SS-HP shows the best comprehensive properties, of which the glass transition temperature (Tg), tensile strength, Young's modulus and toughness are as high as 96 °C, 8.6 ± 0.6 MPa, 188.5 ± 11.2 MPa and 16.3 ± 0.2 MJ m−3, respectively. Besides, its outstanding flexibility could generate reversible shape changes from folding to bending and scrolling. After three scratching-healing cycles, the healing efficiency of LP2-SS-HP at the same location is still above 90% and the transmittance at 550 nm is as high as 88.6%. These remarkable properties demonstrate that LP2-SS-HP is a high performance scrollable and foldable substrate for fabricating transparent healable electrodes.