The effect of blending sulfonated poly(ether ether ketone) with various charged surface modifying macromolecules on proton exchange membrane performance

Modification of sulfonated poly(ether ether ketone) (SPEEK) membrane was attempted by blending three newly developed charged surface modifying macromolecules (cSMMs) having three different polyols. Sulfur content of the cSMMs was analyzed by Fourier transform infra-red spectroscopy and elemental analysis to be in the following order: PEG200-HBS > PEG400-HBS > PPG-HBS, which was also the order for their glass transition temperature (T-g). The control and modified membranes were characterized by contact angle measurement, thermal analysis, X-ray photoelectron spectroscopy, atomic force microscopy and water uptake. The modified SPEEK membrane surfaces were more hydrophilic on the top surfaces than the bottom surfaces as indicated by the water contact angle and by XPS, confirming the stronger migration of cSMM to the top than the bottom surfaces. The cSMM has migrated and formed -SO3 dense layer-like on top and bottom surfaces of the modified membrane. The morphology study of the membrane surfaces showed that the nodule size and surface roughness has also influenced the water uptake, apart from the additional -SO3 group. The modified membranes were tested for methanol permeability and proton conductivity. Employing PEG200-HBS has resulted in the smallest nodule size, the lowest water uptake and the lowest methanol permeability. On the contrary, employing PPG425-HBS had the largest nodule size, the highest water uptake and the highest proton conductivity. The proton conductivity is more dependent on the capability of the membrane to sorb more water rather than the additional -SO3 group introduced by the cSMM. (c) 2008 Elsevier B.V. All rights reserved.