Surface energy and surface composition of end-fluorinated polystyrene

Contact angle analysis was applied to characterize the compositions, surface enrichment and surface energies for a homologous series of fluorosilane-terminated polystyrenes (PS-F) ranging from 5300 to 148 000 g/mol in molecular weight. Surface enrichment of fluorinated end groups was found to decrease with increasing molecular weight but the relative enrichment of end groups (the ratio of the surface to the bulk concentration) increased with increasing molecular weight. Calculations showed that surface segregation greatly affected surface properties with a 3% concentration of end groups yielding a 39% decrease in surface tension and a 0.1% concentration leading to an 8% decrease. The scaling of polymer surface tension with molecular weight for this system was compared with theory and was found to vary with molecular weight, the power law dependence increasing with molecular weight.