Physico-chemical characterization of polyamide NF / RO membranes: insight from streaming current measurements

Tangential streaming current measurements were performed to investigate the surface charge properties and the charge formation mechanism of various NF/RO membranes. Unlike what is usually done in electrokinetic studies of membranes, experiments were conducted with degassed background solutions under a controlled atmosphere by means of nitrogen gas in order to get accurate electrokinetic measurements even in the basic range of pH. It was demonstrated that the streaming current technique implemented with these rigorous experimental conditions is a reliable tool to verify the presence of an additional coating on a commercial TFC membrane. It was also shown that these electrokinetic measurements allow a more clear discrimination between coated and uncoated membranes than the ATR–FTIR technique. Moreover, experiments performed with and without a nitrogen environment revealed specific adsorption of bicarbonate and carbonate ions coming from the dissolution of carbon dioxide in the air onto the surface of RO polyamide membranes containing hexafluoroalcohol functional groups.