Synthesis and characterization of composite membrane by deposition of acrylic acid plasma polymer onto pre-treated polyethersulfone support

Abstract

The plasma techniques were explored to deposit a layer of hydrophilic polymer on asymmetric porous membranes used as support material. Microporous membranes were synthesized by the phase inversion technique from polyethersulfone (PES) and submitted to a surface treatment with RF-plasma of non-polymerizable gas. Carbon dioxide (CO₂) was selected to generate this plasma and to increase the surface energy. Further plasma treatment proceeded with acrylic acid (AA) in vapor phase as source for the permanent surface hydrophilic functionalization. The infrared spectra with horizontal attenuated total reflectance (HATR) show that the deposited plasma polymer provides a high concentration of carbonyl and hydroxyl groups. The hydrophilic polymer layer was evenly deposited, with good adhesion to the support, as was observed by electronic microscopy (SEM). The surface free energy (γ_S) was increased through plasma treatments and confirmed by the decrease of contact angle (θ) measurements and increase of adhesion work (W _a). The nitrogen permeability decreased 650 times; after that a dense thin film was deposited by plasma treatment during 40 min (at 5 W and 8 Pa). Final composite membranes show stability, high surface hydrophilicity, and a surface chemical nature very stable with time.