Abstract

The solubility and aggregation process of polyethoxylated non-ionic surfactants, of general formula C i H2i+1-(O-CH 2-CH2) j -OH with i = 6, 8, 10 and j = 3-6 (C i EO j ), in heptane were studied. The aggregation of C i EO j surfactants in heptane was investigated by using methylene blue (MB) as an absorption probe. In solutions of MB in the presence of these surfactants in heptane, at concentrations larger than the re-dissolution concentration, the UV bands associated to free MB (A 1) and MB-EO complex (A 2) were detected. The ratio of these intensities A 2/A 1, was used to study the kinetics of the complex formation in pure surfactant. The value of A 2/A 1 depends on the surfactant structure and the media wherein MB is dissolved, being larger in the pure surfactant than in heptane solutions. These results are explained in terms of solvent effect and aggregate structures on the complex formation. © 2009 AOCS.