Unusual viscoelasticity behaviour in aqueous solutions containing a photoresponsive amphiphile

Yutaka Takahashi, Yuki Yamamoto, Shinichi Hata, Yukishige Kondo

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)


Here, we report unusual behaviour of the viscoelasticity of surfactant aqueous solutions consisting of cationic cetyltrimethylammonium bromide (CTAB) and an anionic photoresponsive amphiphile, sodium [4-(4-butylphenylazo)phenoxy]acetate (C4AzoNa). When C4AzoNa molecules are trans-isomers, spheroidal micelles are formed in the surfactant solution, the viscosity of which is low. Irradiation of this solution by ultraviolet (UV) light yields an aqueous solution of CTAB/. cis-C4AzoNa (cis-isomers of C4AzoNa), which is a highly viscous gel consisting of wormlike micelles. The drastic change in the surfactant solution viscosity is attributed to the formation and disruption of wormlike micelles. The geometrical structural transformation of the azobenzene groups in the C4AzoNa molecules of the CTAB/C4AzoNa mixture would lead to a change in the critical packing parameter of the mixture, thereby inducing the morphological transformation of the aggregates (spheroidal micelles to wormlike micelles). To our knowledge, this is the first report of a drastic increase in surfactant solution viscosity by UV light irradiation.

Original languageEnglish
Pages (from-to)370-374
Number of pages5
JournalJournal of Colloid and Interface Science
Publication statusPublished - 2013 Oct 1


  • Azobenzene
  • Cationic surfactant
  • Photorheological fluid
  • Self-assembly
  • Viscosity
  • Wormlike micelle


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