A Conductive Hydrophobic Polyaniline Sandwiched Polyvinylidene Fluoride Membrane for Early Detection of Surfactant-Induced Wetting in Membrane Distillation Using Impedance

Wetting of hydrophobic membranes is considered to be one of the major limitations that must be overcome to further the development of membrane distillation technology. Low surface tension liquids can induce wetting, which can significantly affect permeate conductivity after the complete wetting of the membrane pores. In this study, a thin conductive hydrophobic polyaniline (PANI) layer was sandwiched between two nonconductive polyvinylidene fluoride (PVDF) layers by the phase inversion method. The surface of this PANI-PVDF membrane was then electrosprayed with polytetrafluoroethylene to impart superhydrophobicity (water contact angle, ∼160°). Finally, the wetting of membranes was monitored and detected during direct contact membrane distillation of a low surface tension saline feed containing sodium dodecyl sulfate by electrochemical impedance spectroscopy. Compared with measuring conductivity of the permeate side, we found that measuring the cross-membrane impedance at a constant frequency (100 kHz) demonstrated more precise detection and a superior ability in distinguishing different stages of wetting and their intrusion. Further, our experiments demonstrated the possible strategies to elude membrane wetting by flushing distilled water periodically.