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

beta-Cyclodextrin (beta-CD) is a cyclic oligosaccaride with an apolar cavit y that shows a certain degree of selectivity in binding organic and inorgan ic compounds. Lauryl sulfobetaine (LSB) and dodecyltrimethylammonium bromid e (DTAB), having the same hydrophobic and different polar groups are used i n order to compare the influence of the polar group on complex formation wi th beta-CD. The surface tension increased as beta-CD is added to premicella r region of amphoteric (LSB) and cationic surfactant (DTAB) solutions. The relation between the surface tension and surfactant concentration can be ex pressed by the Szyszkowski equation, which combines the Langmuir adsorption model and the Gibbs equation. Binding constants were determined from the e ffect of added beta-CD on the surface tension vs, concentration curves for LSB and DTAB aqueous solutions.