Development of a transparent and stretchable strain sensor based on the dry printing method

Flexible, substrate-based, stretchable sensors have attracted significant attention because they can simulate the complex characteristics of natural skin and have important application value in human motion detection. In this work, we propose a dry printing fabrication method that is performed by mixing carbon nanotubes (CNTs) and silicon dioxide (SiO2) powder, packing it into an SU-8 mold with micro-grid grooves, and then spin coating a small amount of polydimethylsiloxane (PDMS) onto the surface of a PDMS flexible substrate. The coated substrate is then placed on top of the SU-8 mold, so the liquid PDMS can infiltrate the voids in and around the powder. The turning process uses the liquid PDMS's fluidity and permeability to adhere the CNT-SiO2 mixed powder in the SU-8 mold groove to the flexible substrate, and transfers it to the flexible substrate during the substrate's removal process from the mold. The result is a microstructure, conductive layer on the PDMS flexible surface. The conductive layer is coated with conductive silver adhesive, which serves as the electrode, and PDMS is used as the sealing layer to complete the sensor preparation. In this experiment, the sensor performance was controlled by adjusting the mass ratio of CNTs to SiO2. The results show that when the CNTs:SiO2 mass ratio reaches 1:1, the sensor exhibits excellent performance, including GF up to 352 and strain range up to 16%. In addition, the electronic skin (E-skin) also has good transparency, with light transmittance reaching upward of 60%.