Determining Critical Micelle Concentration of Organic Corrosion Inhibitors and its Effectiveness in Corrosion Mitigation

Critical micelle concentration (CMC) of a surfactant corrosion inhibitor is considered to be an important property which may indicate its corrosion mitigation efficiency. One of the common methods to determine a CMC is via surface tension measurements of inhibitor solutions. In this work, the validity of surface tension measurement as an indirect technique for the detection of micelle formation is discussed and tested in conjunction with an alternative method—fluorescence spectroscopy, which was used as a technique that more directly detects micelles in a solution. Results show that surface tension measurements of a quaternary ammonium bromide inhibitor solution, that can determine the concentration at which the water/air interface becomes saturated by the inhibitor molecules, does not always correlate with the formation of micelles. In some cases, the formation of micelles occurred in the same concentration range while in others it happened at much higher concentrations, as determined by fluorescence spectroscopy. Moreover, there was no clear correlation between CMC and maximum inhibition of the corrosion rate.