Spectrophotometric determination of cloud point of Brij 35 nonionic surfactant

The cloud point of nonionic surfactant polyoxyethylene (23) lauryl ether (Brij-35) was determined in the presence of various inorganic electrolytes. The measurements of cloud point (CP) were carried out with UV–vis spectrophotometer instead of visual observation. CP of Brij-35 could not be measured directly because its CP is more than 100 °C. Therefore, CP values of Brij-35 were lowered by the addition of electrolytes. In this study, NaF, NaCl, NaBr, KNO3, K2CO3, K3PO4, Li2SO4, Na2SO4, K2SO4, (NH4)2SO4, CuSO4, ZnSO4, CoSO4 were used as electrolytes. Linear lines which were drawn with CP values were extrapolated to zero electrolyte concentration. The real CP value of Brij-35 which is merely listed as >100 °C in the literature was found as 118.5 ± 0.5 °C for all samples. Furthermore, the effects of the nature of the cation and the anion and the valencies of the cations on CP were reported and the rate of decrease in CP with concentration is discussed.

Research highlights
► The measurements of CP were carried out with UV–vis spectrophotometer instead of visual observation.
► The CP value of Brij-35 which is listed as >100 °C in the literature was found as 119 ± 1 °C with electrolytes.
► Regression equations and regression coefficients (r2) were found from figures.
► The values of CP were found for all electrolytes by using intercepts values obtained from figures.