title: Volume and expansivity changes of micelle formation measured by pressure perturbation calorimetry.
abstract: We present the application of pressure perturbation calorimetry (PPC) as a new method for the volumetric characterization of the micelle formation of surfactants. The evaluation is realized by a global fit of PPC curves at different surfactant concentration ranging, if possible, from below to far above the CMC. It is based on the knowledge of the temperature dependence of the CMC, which can for example be characterized by isothermal titration calorimetry. We demonstrate the new approach for decyl-β-maltopyranoside (DM). It shows a strong volume increase upon micelle formation of 16 ± 2.5 mL/mol (+4%) at 25 °C, and changes with temperature by -0.1 mL/(mol K). The apparent molar expansivity (E(S)) decreases upon micelle formation from 0.44 to 0.31 mL/(mol K) at 25 °C. Surprisingly, the temperature dependence of the expansivity of DM in solution (as compared with that of maltose) does not agree with the principal behavior described for polar (E(S)(T) decreasing) and hydrophobic (E(S)(T) increasing) solutes or moieties before. The results are discussed in terms of changes in hydration of the molecules and internal packing of the micelles and compared with the volumetric effects of transitions of proteins, DNA, lipids, and polymers.
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College St., Toronto, ON M5S 3M2, Canada.
authors.forename: Helen Y
authors.initials: HY
authors.lastname: Fan
authors.forename: Mozhgan
authors.initials: M
authors.lastname: Nazari
authors.forename: Saria
authors.initials: S
authors.lastname: Chowdhury
authors.forename: Heiko
authors.initials: H
authors.lastname: Heerklotz
mesh_terms: D002151:Calorimetry; D057927:Hydrophobic and Hydrophilic Interactions; D008320:Maltose / Q000031:analogs & derivatives / Q000737:chemistry; D008823:Micelles; D011312:Pressure; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D008823:Micelles; D013501:Surface-Active Agents; C411362:dodecyl maltopyranoside; D008320:Maltose