Study of the Polarity and Hydrogen Bond Ability of Sodium Dodecyl Sulfate Micelles by the Kamlet−Taft Solvatochromic Comparison Method

Abstract

We have studied the dipolarity/polarizability (π*), hydrogen bond donor acidity (α), and hydrogen bond acceptor basicity (β) of sodium dodecyl sulfate (SDS) micelles using the Kamlet−Taft solvatochromic comparison method. The micellar environments of solubilized indicator molecules are quite polar (π* = 1.06) and have strong hydrogen bond donating ability (α = 0.87) and moderate hydrogen bond accepting ability (β = 0.40). Both the high dipolarity and especially the strong hydrogen bond acidity support previous work that indicates water is present in the indicators' micellar microenvironments. In contrast to many previous UV−vis spectroscopic studies of the polarity of SDS micelles, we have resolved the recorded micellar spectra so as to obtain the micellar spectrum of the indicators free from contributions of the indicator in the accompanying aqueous phase. This study was conducted to rationalize and complement linear solvation energy relationship (LSER) studies of partitioning in SDS micellar systems which have recently appeared in the literature. To our knowledge this is the first study in which curve resolution is applied to micellar spectra for the purpose of characterizing both the polarity and hydrogen bond ability of SDS micelles.