Eco-friendly fabrication of sandwich-structured poly(imide-siloxane)/silver nanowire composite films for stretchable strain sensors

Polyimide (PI) films have gained significant recognition for aerospace, automotive, displays, microelectronics, and membrane applications due to their excellent mechanical and thermal properties and chemical resistance. However, conventional preparations of PI films have been performed using toxic organic solvents that are harmful to the environment and human health. In this work, stretchable PI films were first prepared using a green aqueous solvent for application as strain sensors. A poly(amic acid-siloxane) salt (PAASS) was synthesized using a solvent mixture (water and <i>tert</i>-butanol) from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), bis(3-aminopropyl)-terminated polydimethylsiloxane (PDMS), and <i>m</i>-phenylenediamine (MPD). The as-prepared aqueous PAASS solutions were drop-cast, and the resultant films were thermally imidized to obtain poly(imide-siloxane) (PIS) films. The films showed excellent elongation at break and 5% decomposition temperature (up to 436.7% and 466 °C, respectively). Stretchable strain sensors were fabricated in the form of sandwich-structured PIS/silver nanowire (AgNW)/PIS composite films. Preliminary strain sensor tests, including stretching/releasing cycles, demonstrated good GF values up to 28.4 and stable sensor performance over the strain range of 5-50% for the PIS/AgNW/PIS composite films. Our study provides an eco-friendly and economical fabrication method for stretchable PIS/AgNW/PIS composite strain sensors that have promising potential for next-generation stretchable device applications.