Encapsulation of ionic polymer-metal composite (IPMC) sensors with thick parylene: Fabrication process and characterization results

Abstract

Ionic polymer-metal composites (IPMCs) tend to have inconsistent sensing properties when operating in air under different humidity levels, or after exposure to different ambient media. Motivated by the need to ensure consistent sensing performance of IPMCs under different ambient environments, in this paper we propose thick (up to 25 micrometers) parylene C coating for IPMC sensors, develop effective coating processes, and evaluate the performance of the encapsulated sensors, along with the comparison with the typical naked IPMC sensors. The proposed fabrication process features the water drive-in step which enables the control and adjustment of the hydration level of an encapsulated IPMC. Experiments are conducted to evaluate the sensing consistency of IPMC sensors in a humidity chamber, first under different humidity levels, and then following exposure to solutions with different cations and different organic solvents. Experimental results show that the proposed thick parylene coating can effectively keep the water content inside the IPMC, isolate the IPMC sensor from various ambient environments, and maintain the sensing consistency, which allows IPMC sensors to be used in practical applications.