The effect of drying condition on the properties of sulfonated and nonsulfonated polysulfone polymer composite membranes

Abstract

In order to keep up the proton conductivity and reduce the methanol permeability of the polymer membranes in the direct methanol fuel cell (DMFC), blend membranes composed of proton conducting component and methanol barrier component were prepared. Highly sulfonated poly(arylene ether sulfone) copolymer with 60mol% sulfonation (sPAES-60) was synthesized via nucleophilic aromatic substitution poly-condensation reaction from 4-4’-biphenol (BP), 3,3’-disulfonated -4’4-dichlorodiphenyl sulfone (SDCDPS), 4-4’-dichlorodiphenyl sulfone (DCDPS) for the proton conducting component. As methanol crossover barrier, poly ether sulfone copolymer (RH-2000, Solvay) was used. Each two polymers were blended with 5:5 blend ratio using MEK/DMF (2:8 weight ratio) mixed solvent. By varying the drying condition (HT, FD1, FD2) and the concentration of casting solution (10wt%, 15wt%, 20wt%) various types of phase separated morphologies were obtained. Important properties of membrane such as proton conductivity, methanol permeability and water uptake were influenced by the morphology. The morphology was characterized by SEM and AFM. The AC impedance spectroscopy was used to measure the proton conductivity and methanol permeability was measured by placing the membrane between two liquid chambers. The cross-sections of blend membranes showed phase separated morphologies. The effect of phase-separated morphology on the properties of blend membranes was investigated. The blend membranes at HT drying condition showed two layer morphology at 10wt% and 15wt% concentrations. HT 20wt%, FD1 10wt% and FD1 15wt% revealed intermediate morphology. Small sPAES-60 domains were interconnected in RH-2000 matrix in the intermediate morphology. FD1 20wt% and all FD2 blend membranes showed as co-continuous morphology. In this thesis, the effect of the concentration of casting solution and the drying condition on the morphology of the blend membrane was investigated. In the conclusion, the trans...