Self-adhesive stretchable conductors for deformation monitoring

Abstract

Recently, research field of stretchable conductors have been gaining a lot of attention because of the high request for human-machine interfaces to be utilized in applications such as wearable electronics as well as smart healthcare. The development of these devices such as wireless implantable strain sensors to measure volume of urinary bladder would allow for long-term monitoring within the bladder, while also allowing to maintain the quality life of the patients suffering from urinary incontinence. Nevertheless, achieving strain sensors with high stretchability as well as having sufficient sensitivity by utilizing simple fabrication methods, still remain as a big challenge. Therefore, SEBS/Au films which possess self-adhesion properties were studied to be the materials for the stretchable strain sensors. The effect of Au film thickness and rate of Au deposition to the performance of the stretchable strain sensors were investigated and optimized as a first step to achieve the target. Moreover, accessible encapsulation method was developed and the effect of the proposed encapsulation method to the stretchability of the strain sensors were also studied. In this project, the SEBS/Au films were fabricated by first preparing SEBS (Styrene-EthyleneButylene-Styrene) film substrate before depositing gold nanoparticles (Au NPs) via thermal evaporation on top of it. Scanning Electron Microscope (SEM) was used to characterize the surface morphologies and study stretchability mechanism of SEBS/Au film. MTS model 43 and Keithley 4200-SCS were simultaneously employed to study the electrical resistance response to the strain applied to determine stretchability and sensitivity of the electrodes. The results showed that a stretchability value of 223.2 ± 10.61% and sensitivity or GF of 21.4 ± 1.7 at 100% strain as well as maintaining the self-adhesion properties when subjected to strain more than 200% were obtained by the stretchable SEBS/Au films with Au film thickness of 40 nm and deposition rate of 0.5 Å/s. Furthermore, encapsulated SEBS/Au films with the encapsulation layer fabricated by spincoating with a spin speed of 200 rpm were recorded to retain 85.36 ± 12.87% of the original stretchability value of the unencapsulated SEBS/Au films. However, further investigations and studies need to be conducted to improve the performance of the strain sensors as there are still a lot of room for development.