Determination of critical micelle concentration of non-ionic surfactants using kinetic approach

摘要

Detergents (or surfactants) when solubilised in water, generally tend to self-associate spontaneously above a particular concentration called the critical micelle concentration (CMC). The CMC of surfactants can be determined by measurements of certain physicochemical parameters of the aqueous system under consideration as a function of surfactant concentration. It is well known that e.m.f. and electrical conductivity methods, as well as surface tension and fluorescence probe techniques, are the most popular methods used in the study of surfactant micellization. The aggregation of surfactants during micellization should influence the kinetic properties of the individual molecules. One may expect that the reactivity towards any species should be different when surfactant molecules are present in mono-meric form in solution, compared with the aggregated form. In micelles, species shield each other to a certain degree. In part, the different kinetic behavior may be due to a drop in the number of targets, as monomers aggregate into fewer large units. A sharp decrease in the reactivity of OH radicals towards surfactants in the aggregated form compared with the monomeric form has been observed using the pulse radiolysis method. This note will attempt to show how the kinetic approach can be used to determine the CMC values for non-ionic Triton X-class surfactants.