Plasma treatment of polysulfone gas separation membranes
The chemical and topographical nature of a polymer surface can be changed by non-equilibrium glow discharge treatment. Surface modification of polysulfone and polyethersulfone was examined using a variety of plasma treatments at a fixed power, pressure and treatment time. The modification observed was found to be dependent upon the type of feed gas employed. Tetrafluoromethane plasmas fluorinate polymer surfaces. The influence of polymeric structure on the extent of modification was examined. Phenyl ring containing polymers experienced a greater extent of modification compared to saturated polymers. The extent of modification is dependent upon both the fluorination mechanism and the surface affinity. Plasmas contain a variety of species accompanied by an electromagnetic spectrum. The role of vacuum ultraviolet radiation in a plasma was investigated as a function of feed gas (argon, krypton, xenon and oxygen) on polyethylene and polystyrene, in an oxygen atmosphere. The xenon vacuum ultraviolet treatment gave rise to the greatest oxidation whilst the O(_2) vacuum ultraviolet treatment was found to result in the least oxidation. The activation mechanisms varied with the feed gas chosen for the experiment. Non-equilibrium glow discharge treatment can alter the transport properties of gases permeating through an asymmetric polysulfone membrane. The selectivity and permeability alter as a function of the treatment. The deposition of a methane plasma polymer onto the surface of the membrane resulted in an increase in the gas flux. Similarly CF(_4) plasma treatment also gave rise to an increase in the gas flux. The deposition of a methane plasma polymer followed by a CF(_4) plasma treatment resulted in a decrease in gas flux and a small increase in the oxygen/nitrogen selectivity.