title: Light-sensitive microemulsions.
abstract: A photodestructible surfactant, sodium 4-hexylphenylazosulfonate (C6-PAS), has been introduced to AOT-stabilized water-in-heptane microemulsions. Proton NMR spectra show that C6-PAS undergoes UV-induced decomposition, to yield a mixture of 4-hexylphenol and hexylbenzene. The photostationary state was determined by 1H NMR, indicating that nearly 90% of the initial photosurfactant had been destroyed, yielding non-surface-active hexylbenzene as the main product. This phototriggered breakdown gives rise to changes in adsorption and aggregation properties of C6-PAS, representing a novel route to induce microemulsion destabilization. When a series of microemulsions containing different amounts of C6-PAS were exposed to UV light, part of the dispersed water phase-separated. Small-angle neutron scattering (SANS) was used to follow the resulting UV-induced shrinkage of the water nanodroplets: a maximum volume decrease was found to be in the order of 60-70%. Kinetic SANS studies were also carried out in order to follow the changes in aggregation as a function of UV irradiation time. Multicontrast SANS experiments gave further insight; for example, it was demonstrated that the shell thickness remained constant. This study represents the first example of light-induced microemulsion destabilization.
authors.affiliation: School of Chemistry, University of Bristol, Bristol, BS8 1TS United Kingdom. julian.eastoe@bristol.ac.uk
authors.forename: Julian
authors.initials: J
authors.lastname: Eastoe
authors.forename: Margarita Sanchez
authors.initials: MS
authors.lastname: Dominguez
authors.forename: Hannah
authors.initials: H
authors.lastname: Cumber
authors.forename: Paul
authors.initials: P
authors.lastname: Wyatt
authors.forename: Richard K
authors.initials: RK
authors.lastname: Heenan