Effect of graphene oxide in the formation of polymeric asymmetric membranes via phase inversion

Membrane morphology of integrally skinned asymmetric membranes made by phase 15 inversion can be tailored by precise control of the thermodynamic properties of the casting 16 solution. In this work, the morphology of polyethersulfone (PES) and polyvinylidene 17 fluoride (PVDF) membranes containing graphene oxide (GO) and their phase separation 18 behavior have been studied. The Flory-Huggins theory and the Hansen solubility 19 parameters have been used to construct theoretical binodal lines for ternary and 20 quaternary systems, which have been validated by conducting cloud titration experiments. 21 Moreover, the effect of different solvents on the morphology of PES membranes is 22 discussed through the thermodynamic and kinetic properties of the casting solutions. 23 Nontoxic solvents dimethyl sulfoxide (DMSO) and dihydrolevoglucosenone (CyreneTM) 24 induce PES/GO membranes with finger-like pores and cellular voids, respectively. The 25 addition of GO in the PES and the PVDF casting solutions increases their thermodynamic 26 instability, leading to thinner selective top layers and higher porosities, up to a point 27 where the high viscosity of the GO-containing solutions hinders the solvent-nonsolvent 28 demixing. The highest porosity and pure water flux (PWF) occurs at 0.1 wt% GO for 29 PES/GO/DMSO and at a loading of 0.3 wt% GO for systems PES/GO/Cyrene and 30 PVDF/GO.