Slot-Die Coating of an On-the-Shelf Polymer with Increased Dielectric Permittivity for Stack Actuators

Nitrile-butadiene rubbers (NBR) have been extensively used as dielectric materials due to their commercial availability, excellent mechanical properties, glass transition temperature below 0 degrees C, and increased dielectric permittivity owing to the presence of polar nitrile groups. Despite these advantages, their processability is poor and cross-linking into thin films is a challenge. Cross-linking requires long times, temperatures exceeding 160 degrees C, and an inert atmosphere. Such cross-linking conditions are incompatible with the continuous manufacturing process of stack actuators. Here, we developed an NBR that can be easily processed into thin films, cross-linked fast, and on-demand by UV-induced thiol-ene reaction in the presence of a dimethoxy-2-phenylacetophenone initiator and 2,2'-(ethylenedioxy)diethanethiol cross-linker. The mechanical properties of the NBR can be easily tuned by the amount of cross-linker used. Additionally, a semi-automated manufacturing process for stack actuators is presented. Here, we slot-die coat the dielectric and spray-coat the electrode through a mask. Because of the commercial availability of the starting materials, an easy and robust protocol for cross-linking, and reproducible manufacturing, it can be envisioned that this material has the potential to replace the well-known acrylate film, VHB, which engineers often use to construct dielectric elastomer actuators in different prototype devices.