Bending actuators with maximum curvature and force and zero interfacial stress

Stress at the interface of a bilayer actuator can lead to delamination, and this stress increases with the difference in the Young's moduli of the two layers. In this study, an actuator that includes a third 'buffer' layer is modeled, and it is shown how optimization of the thickness and modulus of this layer can reduce stress at that interface to zero, with no loss of curvature and only a small loss in force. A polypyrrole (PPy)/ conducting polymer/gold trilayer is used as a model system, with the aim of reducing stress at the weak polymer/gold interface. For a 450 nm thick PPy layer with a Young's modulus of 0.2 GPa, an intermediate layer of 150 nm thickness with a modulus of 5 GPa reduces the stress to zero with no loss of curvature and only a 7% loss in force compared to the bilayer case.