Surface Properties of Poly[2-(perfluorooctyl)ethyl acrylate] Deposited from Liquid CO2 High-Pressure Free Meniscus Coating

The surface characteristics of poly[2-(perfluorooctyl)ethyl acrylate] (PFOEA) films deposited using a high-pressure free meniscus coating (hFMC) process with liquid CO 2 (l-CO 2 ) as the coating solvent on 12.5 cm diameter silicon wafer substrates were investigated using contact angle measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy. The results were compared with surface property measurements of PFOEA films deposited from 1,1,2-trichlorotrifluoroethane (Freon 113) under normal dip coating conditions at atmospheric pressure. NEXAFS measurements showed that perfluoroalkyl groups in the films from l-CO 2 and Freon 113 were well-organized and oriented normal to the substrate at the air/polymer interface. AFM images and XPS measurements revealed that a terrace-like structure of the PFOEA film from l-CO 2 resulted in carbonyl group exposure at the air/polymer interface. This leads to smaller contact angles on the films cast from l-CO 2 relative to the specimens deposited from Freon 113. Annealing the films deposited from the solvents resulted in droplet formation on the surface due to dewetting. The critical surface tension (γ c ) after annealing the film prepared from Freon 113 increased from 6.5 to 8.5 mJ/m 2, whereas γ c of the film deposited from l-CO 2 decreased slightly from 9.7 to 8.9 mJ/m 2 . We discuss how surface morphology changes before and after annealing play a role in the variation of γ c .