Effect of oxalic acid on rheological variation, thermodynamic variaton and formation kinetics in asymmetric membrane formation

The effects of oxalic acid on rheological, thermodynamic and membrane formation kinetics were investigated in polyethersulfone with cardo/oxalic acid(OA)/N, N-dimethylacetamide cast solution. The results show that the addition of OA can work in favor of the enhancement in the demixing of casting solution thermodynamically. The membrane formation kinetics result is different from a commonly accepted conclusion obtained by Strathman et al. that a single linear correlation between square of precipitation front move(L²) and gelation time(t) existed for the whole gelation process. Four different linear correlations between the value of L² and gelation time(t), were identified, these four correlations correspond to four consecutive gelation steps. The maximal gelation rate constant occurred the top layer.