A complete PECVD process for the plasma polymerization of miniature proton
exchange membranes (PEM) is presented. Styrene and trifluoromethane sulfonic
acid are used as plasmagen precursors in a capacitive coupled low pressure
discharge. The process is monitored by impedance probe measurements to
ensure stability and reproducibility. FTIR analyses show that such membranes
are mainly made up of a polystyrene-like matrix with grafted sulfonic acid
groups, which proportion is tuneable as a function of the plasma parameters.
The best results in term of deposition rate, monomer structure retention and
PEM performances are obtained under pulsed plasma conditions, enhancing
radical processes compared to continuous plasma. Because of their thinness
and cross-linked structure, such membranes exhibit a similar proton
conduction ability and a methanol permeability reduced by a factor 150
compared to Nafion$^{\circledR}$. SEM observations show a good
compatibility of plasma polymerized membranes whatever the substrate is.
Consequently, PECVD process enables their better integration in micro fuel
cells compared to conventional spin coating method.