Surface Enrichment of Poly(trifluorovinyl ether)s in Polystyrene Blends

Abstract

Surface modification can be achieved with polymer blends when one component of the system is more surface active than the others. Numerous factors affect the interfacial properties, including the type and concentration of polymers, the solvent, and the interface. Blends of polystyrene (PS) and poly(trifluorovinyl ether) (PTFVE)having a fluorocarbon backbone and an oligoether pendant groupwere cast as films from chloroform or toluene. The air−polymer interface was investigated and found to be enriched with PTFVE at very low bulk concentrations (<1 wt %) as determined by XPS and contact angle analysis. Both surface fluorine and oxygen increased with bulk PTFVE content. Interestingly, PTFVE-enriched surfaces were increasingly hydrophilic with PTFVE content, indicating that oligoether groups were dominant at the outermost 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 blends form similar structures at the interface, with aggregates having PTFVE cores and oligoether coronas, thereby accounting for oligoether pendant groups, and not fluorocarbon backbone, at the air−polymer interface. The nature of the solvent influenced the surface properties of the blends; films cast from toluene, which is a better solvent for PS than chloroform, required greater PTFVE content in the bulk for surface activity than those cast from chloroform. Furthermore, the type of PTFVE used affected surface activity and the resulting surface hydrophilicity.