Highly flexible strain sensors based on polydimethylsiloxane/carbon nanotubes (CNTs) prepared by a swelling/permeating method and enhanced sensitivity by CNTs surface modification

Flexible sensors for large strain detection have recently been attracted the attention of researchers. This investigation reports a stretchable strain sensor in which carbon nanotubes (CNTs) were diffused into polydimethylsiloxane (PDMS) using a facile swelling/permeating method. The CNTs were further modified by using a silane coupling agent (SCA) to improve dispersion and the interaction between CNTs and PDMS. The CNTs permeated the skin layer of the PDMS composite and the inner core of PDMS contained few CNTs, forming a sandwich-like structure. The low CNTs content (0.48 wt%) and sandwich-like structure resulted in excellent composite flexibility which allowed work strains to exceed 350% and Young's modulus to increase from 0.25 MPa to 0.40 MPa. Surface modification of the CNTs improved their permeation depth and dispersion, which was shown to enhance composite sensitivity. The relative resistance change reached 4850% with a gauge factor of 20 by 1.0 wt% SCA modification. Cycled electromechanical properties showed a stable resistance response and sensitivity against strain. Therefore, the PDMS/CNTs nanocomposites prepared by swelling/permeating and CNTs surface modification in this study have various application potentials in the flexible sensor field.