Electric field induced alignment of graphene oxide nanoplatelets in polyethersulfone matrix

In recent years, in order to obtain improved mechanical, thermal, electrical and barrier/transport properties, aligned carbonaceous nanomaterials/polymer nanocomposite films have been receiving growing attention. Correspondingly, the edge oxidized graphene oxide (EOGO) nanoplatelets alignment influence on the structure of the polyethersulfone (PES) membrane films for potential applications in water treatment field has been investigated. Aligned GO/PES nanocomposite membrane films were prepared by non-solvent phase inversion technique after the starting sol phase was preliminarily exposed to high electric fields (50 kV m^-1). Either AC (100, 1000 Hz) or DC mode electric fields were alternatively employed, and the results from both vertical and horizontal field configurations were investigated for structural and morphological comparison. Both XRD, FTIR-ATR, EIS, SEM, TEM and tensile strength analyses were applied in order to characterize the films. The microscopic analyses results have demonstrated successful GO/PES nanocomposite formation and alignment of GO nanoplatelets with the field direction in the matrix at low to moderate (0.02-0.1% wt) GO loadings where the flakes were dispersed and exfoliated sufficiently. However, at higher loading levels (1 and 2% wt) the nanoplateles were mostly agglomerated and the big flakes consisting of irregular plates could not orient their axis parallel to the electric field at the employed field strengths. The results suggest a more effective role of higher frequencies (1000 Hz versus 100 Hz) electric field for alignment of GO nanoplatelets. Simple tensile tests have also similarly confirmed GO alignment under the electric fields at both low (0.1% wt) and moderately high (0.5% wt) GO contents. The tensile strength improvement of the horizontal field processed PES/GO nanocomposite up to 24% compared to its vertical field processed counterpart could be accounted as a proof of the successful alignment of the nanoplatelets. However, EIS results unveiled that non-solvent phase inversion casting method, in its general form, may not be a suitable method for producing materials with tailored properties, due to its random and uncontrollable pore forming mechanism.