Evaluation of encapsulating coatings on the performance of polypyrrole actuators

Conjugated polymer actuators are electroactive materials capable of generating force and movement in response to an applied external voltage. Many potential biomedical and industrial applications require these actuators to operate in a liquid environment. However, immersion of uncoated conducting polymer actuators in non-electrolyte liquids greatly reduces their operating lifetime. Here, we demonstrate the use of spray coating as an effective and simple method to encapsulate polypyrrole (PPy) tri-layer bending actuators. Poly(styrene-b-isobutylene-b-styrene) (SIBS) was used as an encapsulating, compliant spray coating on PPy actuators. A significant enhancement in actuator lifetime in both air and water was observed by encapsulating the actuators. The change in stiffness and reduction in bending amplitude for coatings of different thickness was studied. A simple beam mechanics model describes the experimental results and highlights the importance of coating compliance for actuator coatings. The model may be used to evaluate other possible encapsulating materials.