title: pH-responsive fatty acid self-assembly transition induced by UV light.
abstract: Fatty acids are natural, pH-responsive surfactants. Their properties can be tuned by adding CO2 or by applying light which modify solution pH. We investigated photoresponsive systems based on fatty acids with different chain lengths in the presence of a photoacid generator (PAG). Under UV irradiation, photolysis of the PAG in aqueous solution resulted in a decrease in pH, triggering a change in fatty acid assembly. Using a multi-scale approach before and after UV irradiation, we characterized the effect of this pH decrease on the nature of the fatty acid self-assemblies. At the molecular scale, pH and infrared spectroscopy measurements were used to determine the fatty acid ionization state. At the microscopic scale, the self-assembled structure was characterized using small-angle neutron scattering and microscopy. We showed that UV irradiation tuned the ionization state of the fatty acid molecules which in turn triggered a transition from spherical micelles to vesicles or lamellar phases, depending on fatty acid chain length. We studied the foaming properties of these systems before and after UV irradiation. We showed that after UV irradiation, foam stability was drastically enhanced as a result of a change in self-assembly. Our approach can be easily extended to various pH-responsive surfactants.
authors.affiliation: INRA, UR1268 Biopolymères Interactions Assemblages, F-44316 Nantes, France.
authors.forename: Audrey
authors.initials: A
authors.lastname: Arnould
authors.affiliation: INRA, UR1268 Biopolymères Interactions Assemblages, F-44316 Nantes, France.
authors.forename: Cedric
authors.initials: C
authors.lastname: Gaillard
authors.affiliation: INRA, UR1268 Biopolymères Interactions Assemblages, F-44316 Nantes, France. Electronic address: anne-laure.fameau@nantes.inra.fr.
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Fameau
mesh_terms: D005227:Fatty Acids / Q000138:chemical synthesis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D013501:Surface-Active Agents / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D005227:Fatty Acids; D013501:Surface-Active Agents
keywords: Fatty acid; Light; Photoacid generator; Responsive surfactant; Self-assembly