Temperature dependent physicochemical properties of poly(N-isopropylacrylamide-co-N-(1-phenylethyl) acrylamide) thin films

Abstract

The physicochemical properties of thermo-responsive polymer films are dynamically altered upon changes in environmental conditions. We report on the design and detailed characterization of a novel thermo-responsive polymer film with a temperature transition tuned to fit applications related to the control of marine biofouling. A copolymer consisting of poly(N-isopropylacrylamide) (PNIPAAm) and N-(1-phenylethyl) acrylamide (PEAAm) was synthesized and immobilized as a thin film onto Teflon AF surfaces using a low pressure argon plasma treatment. The temperature dependent physicochemical properties of the thermo-responsive film were thoroughly characterized and the impact of sea water on the film properties was investigated. The immobilized thermo-responsive film exhibits a reversible swelling/deswelling with temperature. Atomic force microscopy showed no morphological changes with varying temperature. Streaming current measurements performed above and below the transition temperature of the thermo-responsive hydrogel indicated that the charging of the polymer/aqueous solution interface is mainly determined by the preferential water ion adsorption at the Teflon AF surface. Inverse contact angles measured using captive air bubbles and analysed by axisymmetric drop shape analysis (ADSA) supported the intrinsic properties of the thermo-responsive film, as surface hydrophilicity decreased with increasing temperature. The advancing water contact angle decreased with increasing temperature, which may be explained by the different molecular mobility at different temperatures, allowing or hampering the re-orientation of hydrophobic segments at the solid–liquid and solid–fluid interfaces. These new films will allow investigations on the interaction of microorganisms with environmentally sensitive surfaces.