‘Artificial Spasmoneme’: Taking Advantage of Diffusion within Asymmetric Structures

Inspired by the motion of ‘Vorticellar’, we have demonstrated reversible coiling and uncoiling motions in polymeric micro-actuators. The actuators were fabricated in the form of ribbon-shape patterns by the evaporation induced self-assembly of dual-stimuli responsive polymers.
The reversible transformation between extended ribbon and contracted helix was induced by temperature or pH due to changes in the interfacial energy associated with the phase transition across the material-defined lower critical solution temperature. For the case of pH driven phase-transition, the speed was improved by a factor of 20 as compared to temperature driven contraction. This enhanced speed of contraction is hypothesized to be associated with the large transient deformations caused by the swelling and deswelling processes. We have developed a numerical model for relating the curvature-time relationship to the initial geometry and material properties. This new insight of controlling diffusion-induced volume change has opened up new opportunities for predicting more complicated phenomena, such as bi-stable snapping.