A Yin-Yang complementarity strategy for design and fabrication of dual-responsive bimorph actuators

Multi-responsive soft actuators that can convert environmental energies to mechanical works are promising for robotics. However, it currently lacks universal and effective concepts to develop dual-responsive bimorph actuators. In this paper, the concept of Yin-Yang complementarity, a classical theory in the history of Chinese philosophy, has been adopted for designing dual-responsive actuators. The complement of Yin and Yang means the bilayers can be inter-constraint as well as being complementary in a dual-responsive actuation. As a proof-of-concept, a composite layer of nano-size graphite (Nano-G) and polyvinylidene fluoride (PVDF) has been combined with graphene oxide (GO), forming a bilayer structure. In response to moisture, GO is positive, meaning Yang, whereas Nano-G@PVDF is negative, meaning Yin. On the contrary, under light irradiation, GO is negative; whereas the photothermal Nano-G@PVDF layer is positive. We demonstrated a bi-directional walking robot and a smart claw array for controllable moisture/light manipulation. The Yin-Yang complementarity strategy provides a universal concept for developing multi-responsive bimorph actuators.