Origins of the Gain in Hydrophobicity of Polystyrene Linked to the Addition of Tailored Fluorinated Oligo-Polystyrene Additives
Résumé
This work aims at understanding the effect of random perfluorinated polystyrene (PS) copolymers added in a PS matrix to enhance its hydrophobic properties. Three synthetized random fluorinated copolymers, named POISE-a (Polymer prOcessing Interface StabilizEr), with various amounts of chemically bonded fluorine were blended with a commercial PS matrix by a solvent-cast process. Their effects on the static wettability properties of PS were studied with water. It was noticed that the static contact angle increases with the additive content according to a sigmoidal law, from 95 to 116°, depending on the type of POISE-a. To decorrelate the chemical and physical effects on the wetting properties, analyses of the morphology of the polymer blends were undertaken using optical microscopy and laser confocal microscopy measurements. These analyses allowed us to show that the increase of the contact angles of the PS/POISE-a blends was mainly due to the chemical heterogeneities of the surface of the films, and in particular with the formation of crystalline fluorine-rich nodules. A singular hydrophobic behavior was evidenced for PS/POISE-a blends containing 20 mol % of the fluorinated comonomer and has been related to their specific structures, showing an interdigitation of the fluorinated chains at a nanoscale leading to nodules more homogeneously distributed in the PS matrix at a microscale.