Surface enrichment of poly(trifluorovinyl ether)s in polystyrene blends

Surface modification can be achieved with polymer blends when one component of the system is more surface active than the others. Numerous factors aff ect the interfacial properties, including the type and concentration of pol ymers, the solvent, and the interface. Blends of polystyrene (PS) and poly( trifluorovinyl ether) (PTFVE)-having a fluorocarbon backbone and an oligoet her pendant group-were cast as films from chloroform or toluene. The air-po lymer interface was investigated and found to be enriched with PTFVE at ver y low bulk concentrations (<1 wt %) as determined by XPS and contact angle analysis. Both surface fluorine and oxygen increased with bulk PTFVE conten t. Interestingly, PTFVE-enriched surfaces were increasingly hydrophilic wit h PTFVE content, indicating that oligoether groups were dominant at the out ermost layer. This observation was confirmed by angle-resolved XPS and ToF SIMS. AFM of PTFVE cast on mica indicated the presence of large aggregates on the order of 200 nm in diameter. We hypothesize that PTFVE in PS/PTFVE b lends form similar structures at the interface, with aggregates having PTFV E cores and oligoether coronas, thereby accounting for oligoether pendant g roups, and not fluorocarbon backbone, at the air-polymer interface. The nat ure of the solvent influenced the surface properties of the blends; films c ast from toluene, which is a better solvent for PS than chloroform, require d greater PTFVE content in the bulk for surface activity than those cast fr om chloroform. Furthermore, the type of PTFVE used affected surface activit y and the resulting surface hydrophilicity.