Hybrid PVDF/PVDF-graft-PEGMA Membranes for Improved Interface Strength and Lifetime of PEDOT:PSS/PVDF/Ionic Liquid Actuators

The exploitation of soft conducting polymer-based actuators suffers from two main shortcomings: their short life cycle and the reproducibility of the fabrication techniques. The short life cycle usually results from the delamination of the components due to stresses at the interface during the actuation. In this work, to achieve strong adhesion to poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) electrodes, the wetting properties of the surface of a polyvinylidene fluoride (PVDF) membrane are improved using argon-plasma-induced surface polymerization of poly(ethylene glycol) monomethyl ether methacrylate (PEGMA). Hybrid membranes are created with hydrophilic PVDF-graft-PEGMA outer surfaces and hydrophobic bulk. The width of each layer is controlled by spray coating, as it allows for the deposition of the reaction precursor to a certain depth. Subsequently, a PEDOT:PSS water solution fills the pores of the functionalized part of the membrane and a mixing layer between PEDOT:PSS and PVDF is created. We also show that PVDF-graft-PEGMA copolymers play an important role in binding the membrane to the electrodes and that direct mechanical interlocking in the pores can further improve the adhesion. Finally, PEDOT:PSS/PVDF-graft-PEGMA/PEDOT:PSS actuators are made by simple solution casting. They are capable of producing high strains of 0.6% and show no signs of delamination after more than 150 h or 10(4) actuation cycles. Furthermore, the preservation of the hydrophobic membrane in between two PEDOT:PSS layers increases the resistance between them from 0.36 Omega to 0.16 M Omega, thus drastically modifying the power dissipation of the actuators.