Electrospun polyamide-6 nanofiber for hierarchically structured and multi-responsive actuator

Actuators that can respond mechanically to external stimulus have attracted great interests because of their great potential in applications of artificial muscle, soft robot, sensor, power generator, and so on. However, the creation of low-cost and multi-responsive actuators from conventional materials is still challenging. Herein, we demonstrate a new kind of hierarchically structured and multi-responsive actuator by twisting electrospun polyamide-6 into coiled yarn (CPY). Due to the presence of microscale and nanoscale cavities, the CPY can reversibly rotate in response to various organic solvents, and the rotation speed is depended on the type of solvent. Capillary force driven shrinkage is suggested as the actuating mechanism of our CPY, which is different from all previously reported coiled yarns. The high coefficient of thermal expansion of polyamide-6 also makes the CPY heat responsive, as the CPY shows contraction upon heating due to the volume expansion induced untwisting. In addition, NIR light and water responsiveness can be further inserted into the CPY by modifying the non-woven with polydopamine prior to twisting as demonstrated here. (C) 2019 Elsevier B.V. All rights reserved.