Enhancement of polycarbonate membrane permeability due to plasma polymerization precursors

The diffusivity of different species through a membrane depends on several factors to illustrate the structure of the matrix, molecular size and concentration of the species and temperature. This study concerns the use of the low-pressure plasma process with different monomers to confer surface chemical character to polycarbonate membranes without altering their bulk properties for change membrane permeability. Track-etched polycarbonate membranes with 0.03 mu m pore sizes were modified by plasma polymerization technique with two precursors; acrylic acid and allylamine in radio frequency discharge at certain plasma process conditions (discharge power: 20 W, exposure time: 10 min, frequency: 13.56 MHz). The transport properties of model organic acid (citric acid) was studied through unmodified and modified polycarbonate membranes by using diffusion cell system. Such plasma treated membranes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and surface energy changes were studied by static contact angle measurements. These results showed that the change of surface properties could be used to improve the transport properties of the target substrates. The diffusion of citric acid through plasma treated polycarbonate membrane was increased about 54.1 +/- 3.5% with precursor: allylamine while it was decreased 48.7 +/- 2.5% with precursor acrylic acid. It was observed that the presences of proper functional group (like amino) in surfaces of pores can raise the affinity to citric acid and improve its transport rate. (C) 2012 Elsevier B. V. All rights reserved.