| AVS 61st International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF-MoA |
| Session: | Self-Assembled Monolayers, Layer-by-Layer Assemblies, and Hydrophobic/Amphiphobic Thin Films |
| Presenter: | Anna Maria Coclite, Graz University of Technology, Austria |
| Authors: | A.M. Coclite, Graz University of Technology, Austria C. Ranacher, Graz University of Technology, Austria |
| Correspondent: | Click to Email |
Proton conductive copolymers of perfluorodecylacrylate (PFDA) and methacrylic acid (MAA) are synthesized by initiated Chemical Vapor Deposition (iCVD). The MAA provides the –COOH groups useful to conduct protons, while the PFDA is responsible for creating the hydrophobic backbone to stabilize the structure during tests in water. The ultimate goal is to use these copolymers as proton exchange membranes in fuel cells. Preliminary experiments have shown that proton conductivities in the range of 70 mS/cm can be reached with these copolymers.1 The aim of the new research is to study the effect of preferred crystallographic orientation on the proton conductivity and water / temperature stability of the copolymers. Preferred crystallographic orientation (texture) in thin films frequently has a strong effect on the properties of the materials and it is important for stable surface properties. Poly-PFDA has a high tendency to give organized molecular films. Crystalline poly-PFDA have been fully obtained also by iCVD.2 The degree of crystallinity and the preferred orientation of the perfluoro side chains, either parallel or perpendicular to the surface, can be controlled by tuning the CVD process parameters (i.e. initiator to monomer flow rate ratio, filament temperature, and substrate temperature). Super-hydrophobicity (advancing water contact angle, WCA, of 160°, low hysteresis of 5°), and oleophobicity (advancing CA with mineral oil of 120°) were achieved.3 Low water contact angle hysteresis was obtained with high crystallinity, particularly when the orientation of the crystallites resulted in the perfluoro side groups being oriented parallel to the surface. The latter texture resulted in smoother film (RMS roughness < 30 nm) than the texture with the chains oriented perpendicularly to the surface. This can be very advantageous for our application that require smooth but still crystalline films. When the PFDA is copolymerized with MAA, the degree of crystallinity decreases and therefore also the stability in water, but the proton conductivity increases due to the higher number of acid groups embedded in the structure. A good trade-off has been obtained when using 20% of MAA in the gas feed.
1 A.M. Coclite et al., Polymer, 2013, 54, 24-30
2 A. M. Coclite et al., Adv. Funct. Mater. 2012, 22, 2167–2176
3 A. M. Coclite et al., Adv. Mater. 2012, 24, 4534–4539