Selective localization of multi-walled carbon nanotubes in thermoplastic elastomer blends: An effective method for tunable resistivity-strain sensing behavior

Conductive network morphology and interfacial interaction play important roles in determining resistivity-strain (ρ-ε) sensing behavior of conductive polymer composites (CPCs). In this work, thermoplastic elastomer blends consisting of poly(styrene-butadiene-styrene) block polymer (SBS) and thermoplastic polyurethane (TPU) were fabricated via different melt processing procedures, which could tune the above two issues simultaneously by selectively localizing multi-walled carbon nanotubes (MWCNTs) in SBS, TPU and both in SBS and TPU, respectively. It is observed that the composite fibers with selectively localized MWCNTs show distinct different ρ-ε sensing behavior. Work of adhesion calculation suggests stronger interfacial interaction between MWCNTs and SBS, however, wetting coefficient calculation indicates slightly better wetting of MWCNTs with TPU. Because of such stronger interaction and poorer dispersion, the composite fiber with MWCNTs distributed in SBS exhibits higher ρ-ε sensitivity than its counterpart with MWCNTs distributed in TPU, and with MWCNTs distributed in both phases, the ρ-ε sensitivity lies in between. Moreover, the ρ-ε sensing behavior was fitted with a model based on tunneling theory by Simmons. It is suggested that the change in tunneling distance and the number of conductive pathways could be accelerated significantly under strong interfacial interaction. This study could offer a new pathway and provide a guideline for the preparation of high-performance CPC resistivity-strain sensors with tunable sensitivity.