The temperature coefficient of the c lattice parameter of polyethylene; an example of thermal shrink̄age along the chain direction

The application of twisted and coiled synthetic fibers for energy conversion is promising due to their flexibility, lightweight and wearability. Although there are significant efforts on improving the performance of twisted and coiled polymer fibers, new understanding is still required about possible effects of the fabrication parameters and the precursor fiber type on thermal actuation performance and energy conversion efficiency. Herein, two types of coiled actuators were fabricated by inserting certain numbers of twists to polyamide 6 (PA6) single fibers and yarns, and the effects of twisting numbers and precursors type on actuation responses, physical properties, and structural changes were investigated. It was demonstrated that fiber-based and yarn-based actuators had different actuation properties where the former one showed a greater actuation load and the latter one had a faster torsional actuation. Also, the yarn-based samples generated faster torsion actuations with the rotation speed up to 16,000 rpm/m, and presented higher thermal actuation sensitivity. Depending on the obtained characteristics, the prepared actuators were used in developing smart textiles for different applications such as fabricating small spring-like robot, smart curtains, and infrared-sensitive functional gloves.