Thermally-activated locomotion of a bilayer polymer actuator

The development of smart actuators based on renewable or biocompatible materials, which are able for delivery of specific cargo is of great importance in robotics, medical and material science engineering, food industry, etc. Here, we report the original design of a bilayer polymer actuator consisting of two polymer materials with an interface adhesive layer between them, able for macroscopic locomotion step by step on a special ratchet substrate through repetitive bending and straightening. This was triggered by heat alternation due to incandescent lamp radiation on/off switching, with a rapid reaction time of the actuator to heat exposure of the order of few seconds. Specifically, a relatively fast locomotion of the actuator was achieved due to the large amplitude of its reversible bending deformation of up to ∼40% measured in terms of the actuator's elevation-to-length ratio. As a result, a typical actuator demonstrated the locomotion velocity of about 3 cm/min, where each cycle of contraction/expansion yielded a walking step of ∼1 cm for about 20 s. It was demonstrated that the actuator, while moving, is able to carry a cargo almost twice heavier than the mass of the carrier itself. Based on optical microscopy and atomic force - infrared spectroscopy data it was concluded that the adhesive interface layer plays an important role in the stable operation of the actuator as it retards linear expansion of the rear polymer layer and thus assists conversion of different linear expansion of the adjacent layers into their effective bending.