title: Light-responsive viscoelastic fluids based on anionic wormlike micelles.
abstract: A new class of light-responsive viscoelastic fluids based on anionic wormlike micelles is reported. The key components are sodium oleate (NaOA) and a cationic azobenzene dye, 1-[2-(4-phenylazo-phenoxy)-ethyl]-3-methylimidazolium bromide (C0AZOC2IMB). These binary systems are gel-like fluids at certain concentration ratios of [C0AZOC2IMB]/[NaOA], e.g. 35/100, owing to the formation of long, entangled wormlike micelles. The viscosity of these fluids can be controlled reversibly by light due to photo isomerization between trans-C0AZOC2IMB and cis-C0AZOC2IMB. For example, the zero-shear viscosity (η0) of an originally gel-like sample is high up to ~1300 Pa s when C0AZOC2IMB is in its trans from, whereas the mixture becomes a Newtonian fluid with η0 about 0.01 Pa s after UV light irradiation. For the post-irradiated cis-C0AZOC2IMB, short cylindrical micelles form, hence accounting for the lower viscosity. Evidence for the structural transition is provided by UV-vis spectra, rheology, (1)H NMR and cryo-transmission electronic microscopy measurements.
authors.affiliation: College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, PR China.
authors.forename: Yechang
authors.initials: Y
authors.lastname: Lu
authors.forename: Tengfei
authors.initials: T
authors.lastname: Zhou
authors.forename: Qing
authors.initials: Q
authors.lastname: Fan
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Dong
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Li
keywords: Cylindrical micelles; Light-responsive systems; Self-assembly; Viscosity; Wormlike micelles