title: Effect of salts on the phase behavior and the stability of nanoemulsions with rapeseed oil and an extended surfactant.
abstract: For many decades, the solubilization of long-chain triglycerides in water has been a challenge. A new class of amphiphiles has been created to overcome this solubilization problem. The so-called "extended" surfactants contain a hydrophilic-lipophilic linker to reduce the contrast between the surfactant-water and surfactant-oil interfaces. In the present contribution, the effects of different anions and cations on the phase behavior of a mixture containing an extended surfactant (X-AES), a hydrotrope (sodium xylene sulfonate, SXS), water, and rapeseed oil were determined as a function of temperature. Nanoemulsions were obtained and characterized by conductivity measurements, light scattering, and optical microscopy. All salting-out salts show a transition from a clear region (O/W nanoemulsion), to a lamellar liquid crystalline phase region, a clear phase (bicontinuous L(3)), and again to a lamellar liquid crystalline phase region with increasing temperature. For the phase diagrams with NaSCN and Na(2)SO(4), only one clear region (O/W nanoemulsion) was observed, which turns into a lamellar phase region at elevated temperatures. Furthermore, the stability of the nanoemulsions was investigated by time-dependent measurements: the visual observation of phase separation, droplet size by dynamic light scattering (DLS), and optical microscopy. The mechanism of the different phase transitions is also discussed.
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany.
authors.forename: Angelika
authors.initials: A
authors.lastname: Klaus
authors.forename: Gordon J T
authors.initials: GJ
authors.lastname: Tiddy
authors.forename: Conxita
authors.initials: C
authors.lastname: Solans
authors.forename: Agnes
authors.initials: A
authors.lastname: Harrar
authors.forename: Didier
authors.initials: D
authors.lastname: Touraud
authors.forename: Werner
authors.initials: W
authors.lastname: Kunz
mesh_terms: D003460:Crystallization; D004553:Electric Conductivity; D004655:Emulsions; D005229:Fatty Acids, Monounsaturated; D057927:Hydrophobic and Hydrophilic Interactions; D008853:Microscopy; D049329:Nanostructures; D044367:Phase Transition; D010938:Plant Oils / Q000737:chemistry*; D000074262:Rapeseed Oil; D012492:Salts; D013053:Spectrophotometry; D013431:Sulfates / Q000737:chemistry; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D013861:Thiocyanates / Q000737:chemistry; D014280:Triglycerides / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014992:Xylenes / Q000737:chemistry
chemical_list: D004655:Emulsions; D005229:Fatty Acids, Monounsaturated; D010938:Plant Oils; D000074262:Rapeseed Oil; D012492:Salts; D013431:Sulfates; D013501:Surface-Active Agents; D013861:Thiocyanates; D014280:Triglycerides; D014992:Xylenes; D014867:Water; C012036:sodium sulfate; C024553:sodium thiocyanate