title: Hydrotrope-induced inversion of salt effects on the cloud point of an extended surfactant.
abstract: We report on the effects of electrolytes spanning a range of anions (NaOc, NaSCN, NaNO(3), NaBr, NaCl, NaBu, NaOAc, Na(2)SO(4), Na(2)HPO(4), and Na(2)CO(3)) and cations (LiCl, NaCl, KCl, CsCl, and choline chloride) on the aqueous solubility of an extended surfactant. The surfactant is anionic with a long hydrophobic tail as well as a significant fraction of propylene oxide groups and ethylene oxide groups (C(12-14)-PO(16)-EO(2)-SO(4)Na, X-AES). In the absence of electrolytes, X-AES exhibits a cloud-point temperature that decreases with increasing surfactant concentration. After the addition of salts to the surfactant solutions, various shifts in the solubility curves are observed. These shifts follow precisely the same Hofmeister series that is found for salting-in and salting-out effects in protein solutions. In the presence of different concentrations of sodium xylene sulfonate (SXS), the solubility of the surfactant increases. In this context, SXS can be considered to be a salting-in salt. However, when the electrolytes are added to an aqueous solution of X-AES and SXS the Hofmeister series reverses for divalent anions such as Na(2)SO(4), Na(2)HPO(4), and Na(2)CO(3). Studies on the phase behavior and micelle structures using polarization microscopy, freeze-etch TEM, and NMR measurements indicate a dramatic change in the coexisting phases on the addition of SXS.
authors: Institute of Physical and Theoretical Chemistry, Faculty of Natural Sciences III, University of Regensburg, D-93040 Regensburg, Germany.
authors: Angelika
authors: A
authors: Klaus
authors: Gordon J T
authors: GJ
authors: Tiddy
authors: Reinhard
authors: R
authors: Rachel
authors: Anh Phong
authors: AP
authors: Trinh
authors: Eva
authors: E
authors: Maurer
authors: Didier
authors: D
authors: Touraud
authors: Werner
authors: W
authors: Kunz
mesh_terms: D000838:Anions; D011232:Chemical Precipitation; D004573:Electrolytes / Q000737:chemistry; D008823:Micelles; D044367:Phase Transition / Q000187:drug effects; D011506:Proteins; D012492:Salts / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D000838:Anions; D004573:Electrolytes; D008823:Micelles; D011506:Proteins; D012492:Salts; D013501:Surface-Active Agents