A facile method of surface modification for hydrophobic polymer membranes based on the adhesive behavior of poly(DOPA) and poly(dopamine)

Hydrophobic polymer membranes were surface-modified by coating 3,4-dihydroxyphenylalanine (DOPA) and dopamine. The DOPA and dopamine self-polymerized and adhered firm to the membrane surfaces in mild aqueous environments. The membrane surface hydrophilicity was evaluated through water contact angle measurement. It was found that the water contact angle of the modified membranes reduced remarkably compared with the corresponding original membranes, suggesting that the membrane hydrophilicity was significantly improved. The changes in the chemical compositions of membrane surfaces were determined by X-ray photoelectron spectroscopy (XPS). Morphological changes of membrane surfaces were described using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The experimental results indicated the polymer layers containing carboxyl, hydroxyl and amino groups were substantially attached onto the membranes by the strongly interaction between poly(DOPA)/poly(dopamine) and membrane surfaces. This facile method was effectual to polyolefin porous membranes including polyethylene (PE), poly(vinylidene fluoride) (PVDF) and polytetrafluoroethylene (PTFE). The water fluxes for these membranes were also elevated after coating.