The effect of fluorinated surface modifying macromolecules on the surface morphology of polyethersulfone membranes

Polyethersulfone (PES) has been recently adopted for membrane materials in applications such as ultrafiltration and haemodialysis. As a biomaterial, t he factors which affect the blood compatibility of PES membranes include su rface energetics, hydrophobicity, and surface morphology. Surface fluorinat ion of materials has been found to create surfaces with improved blood comp atibility and chemical stability. One never approach to generating fluorina ted polymer surfaces has included the use of fluorinated surface modifying macromolecules (SMMs). These macromolecules have been reported to establish fluorinated functional groups at surfaces of polymeric materials without s ignificantly affecting the physical properties of the base polymer. However , to date there has been relatively little information published on the nat ure of the surface structure for PES materials containing these SMMs. In th is study, synthesized SMMs with varying chemical compositions were characte rized and blended with PES, and fabricated into flat sheet membranes. The b ulk thermal transitions of PES materials were not significantly altered by the addition of 4 wt% SMMs. Contact angle data showed that the addition of SMMs in PES created more hydrophobic surfaces, accompanied by an increase i n surface heterogeneity. X-ray photoelectron spectroscopy studies confirmed the presence of elemental fluorine at the surface. Through microscopy stud ies, it was shown that surface modification was achieved by the migration o f SMM concentrated microdomains to the air-membrane interface. The generate d microdomains (approximately 1-2 mum in diameter) are dispersed within the top 8 mum of the surface. The concentration of microdomains was gradually depleted from the surface to the bulk of the membrane. A schematic of the m orphology for SMMs within the PES membrane surface was proposed.