Study of the Polarity and Hydrogen-Bond Ability of Dodecyltrimethylammonium Bromide 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 dodecyltrimethylammonium bromide (DTAB) micelles using the Kamlet−Taft solvatochromic comparison method. DTAB micelles were found to be quite polar (π* = 1.02), to have relatively strong hydrogen-bond donating ability (α = 0.700), and to have moderate hydrogen bond accepting ability (β = 0.486). These values are compared to the π*-, α-, and β-values of sodium dodecyl sulfate (SDS) micelles obtained in a previous solvatochromic study and are found to be qualitatively consistent with linear solvation energy relationship studies of both SDS and DTAB micellar systems. The chemical interpretation of these parameters and the nature of DTAB micelles which they reflect are discussed. By comparison to the solvatochromic parameters of representative pure solvents such as DMSO (π = 1.00), 2-propanol (α = 0.69), and ethylbenzoate (β = 0.43), it is evident that the micellar environments observed by the various indicators are quite dipolar, very strong hydrogen bond donors, and moderately strong hydrogen bond acceptors.