Fabrication and characterization study of ultrathin multi‐walled carbon nanotubes/polydimethylsiloxane composite membranes for strain sensing application

Abstract Conductive polymer composite membranes such as multi‐walled carbon nanotubes (MWCNTs)/polydimethylsiloxane (PDMS) membranes are important for flexible strain sensors. However, ultra‐thin MWCNTs/PDMS films (<20 μm) have rarely been studied, mainly due to inherent difficulties in fabricating processes such as the peeling and transferring. In this work, the filtration‐from‐suspension (FFS) method was used to fabricate ultra‐thin layer of MWCNTs (buckypapers, BPs). Subsequently, spin‐coating PDMS on the BPs was carried out, and the penetration of PDMS into BPs was promoted under vacuum conditions to obtain the MWCNTs/PDMS composite films. The elastic nature of PDMS assisted in peeling the composite films off the filter papers. Compared with the other methods, the fabrication method of MWCNTs/PDMS membranes in this paper is more time‐efficient and reliable. A comprehensive study on the fabricated MWCNTs/PDMS membranes with different compositions was carried to understand the mechanical and electrical performance under static and cyclic loading conditions. The obtained stress–strain and resistance‐strain curves show that the modulus of the MWCNTs/PDMS membrane can be significantly increased over 8–10 times compared with pure PDMS membranes. The near exponential relationship between the resistance change versus the strain implies the MWCNTs/PDMS membranes are suitable for strain sensors. Moreover, we find there is a stability transition point in thickness at which the MWCNTs/PDMS composite membrane exhibits the best overall integrated performance. At this point, the changes before and after cyclic loading/unloading on composite membranes is almost negligible, implying the good reliability of the sensing membranes. This study has demonstrated the feasibility of fabricating ultrathin MWCNTs/PDMS membranes for wearable sensors.