Self-Assembly of a Nonionic Photoresponsive Surfactant under Varying Irradiation Conditions:  A Small-Angle Neutron Scattering and Cryo-TEM Study

• Published in: Langmuir Vol. 22; no. 4; pp. 1436 - 1442
• Main Authors: Shang, Tiangang, Smith, Kenneth A, Hatton, T. Alan
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14.02.2006
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Membranes; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Vesicle; Self assembly; Transmission electron microscopy; Small angle neutron scattering; Photoisomerization; Non ionic surfactant; Surfactant; Aggregate; Structure; Glycol; Azobenzene; Isomer
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la052215y

We have used small-angle neutron scattering (SANS), and cryogenic transmission electron microscopy (cryo-TEM) to determine the structure of aggregates formed by the photoresponsive surfactants diethylene glycol mono(4‘,4-butyloxy, butyl-azobenzene) (C4AzoOC4E2) and diethylene glycol mono(4‘,4-hexyloxy, butyl-azobenzene) (C4AzoOC6E2) under different illumination conditions. At high concentrations, the self-assembly behavior of these surfactants changes remarkably in response to different radiation conditions. The trans isomers assemble into bilamellar (C4AzoOC4E2) and unilamellar (C4AzoOC6E2) vesicles, while the cis isomers (under UV light) form bicontinuous phases. These light-induced structural changes are attributed to a change in the sign of the Gaussian rigidity, which is the direct result of azobenzene photoisomerization.