Controllable distribution of conductive particles in polymer blends via a bilayer structure design: a strategy to fabricate shape-memory composites with tunable electro-responsive properties

Abstract

Electro-responsive shape-memory composites (ESMCs) are a type of advanced smart materials, which are of significant interest in the self-driven device field. In this study, a series of thermoplastic polyurethane/polycaprolactone/multi-walled carbon nanotube (TPU/PCL/MWCNT) bilayer ESMCs were fabricated via the hot lamination of MWCNT-filled TPU and pure PCL, pure TPU and MWCNT-filled PCL, and MWCNT-filled TPU and MWCNT-filled PCL, while maintaining the overall amount of MWCNTs at ∼2.5 wt%. By tuning the assembly method, a controllable distribution of MWCNTs in the TPU layer as the memorizing phase and a PCL layer as the switching component was easily realized. As compared to the conventional blending composite (CBC) that contains the same compositions, the bilayers showed a much larger electrical conductivity because the confined layer space promoted filler connection, especially when MWCNTs were dispersed in PCL. In addition, the bilayers composed of continuous TPU could provide a stronger driving force when activated by an electric field, showing a better shape recoverability than that of CBC. With the manipulation of applied voltage and MWCNT distribution, the bilayer composites could achieve an excellent shape recovery ratio above 97.0% below 20 V. Specifically, the specimen with a confined distribution of MWCNTs in PCL was able to finish almost an entire self-deployment at an extremely low voltage of 5 V. This work develops a new strategy to fabricate ESMCs with tunable performances, which is expected to be applicable to other combinations of shape-memory systems and conductive particles. The materials presented herein have promising application prospects in sensors, actuators, aerospace devices, and so forth.