Modeling the Micellization Behavior of Mixed and Pure n-Alkyl-Maltosides

Abstract

The micellization behavior of a series of n-alkyl-maltosides in aqueous solution was studied by isothermal titration calorimetry (ITC) and dynamic light scattering (DLS) at 25 degrees C. Demicellization experiments were conducted with single component micelles of octyl (OM), nonyl (NM), decyl (DM), undecyl (UM), and dodecyl (lauryl, LM) maltoside and binary mixtures of LM with OM, NM, DM and UM, respectively. A model was derived on the basis of the pseudophase approximation to fit the complete demicellization curves. It yielded good global fits of the curves obtained at different mixing ratios and ranging over >3 orders of magnitude in concentrations. It provides a quantitative explanation for the two-range coassociation behavior of the surfactant mixtures also in the absence of second critical micelle concentration (CMC) phenomena. The hydrodynamic radius, RH, of the mixed micelles was the average of that of the pure components as seen by noninvasive backscattering (NIBS) DLS. Methylene group contributions were constant for octyl through myristyl chains, amounting to -3.1 kJ/mol for the standard free energy and -1.8 kJ/mol for the enthalpy of micellization. RH increased by 0.25 nm per methylene.