Surface tension studies of lauryl sulfobetaine - beta-cyclodextrin and dodecyltrimethylammonium bromide - beta-cyclodextrin inclusion complexes in aqueous solution

Abstract

beta-Cyclodextrin (beta-CD) is a cyclic oligosaccaride with an apolar cavity that shows a certain degree of selectivity in binding organic and inorganic compounds. Lauryl sulfobetaine (LSB) and dodecyltrimethylammonium bromide (DTAB), having the same hydrophobic and different polar groups are used in order to compare the influence of the polar group on complex formation with beta-CD. The surface tension increased as beta-CD is added to premicellar region of amphoteric (LSB) and cationic surfactant (DTAB) solutions. The relation between the surface tension and surfactant concentration can be expressed by the Szyszkowski equation, which combines the Langmuir adsorption model and the Gibbs equation. Binding constants were determined from the effect of added beta-CD on the surface tension vs, concentration curves for LSB and DTAB aqueous solutions.