UV Causes Dramatic Changes in Aggregation with Mixtures of Photoactive and Inert Surfactants

• Published in: Langmuir Vol. 20; no. 15; pp. 6120 - 6126
• Main Authors: Eastoe, Julian, Sanchez Dominguez, Margarita, Wyatt, Paul, Orr-Ewing, Andrew J, Heenan, Richard K
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20-07-2004
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la0496486

Aqueous mixtures of photosensitive and inert surfactants have been prepared; photoreactions and changes in aggregation after irradiation have been characterized. The photosensitive component was a stilbene-containing gemini photosurfactant (E-SGP), and the inert surfactants were either DTAB (dodecyltrimethylammonium bromide) or one of two different gemini surfactants, 12-4-12 or 16-4-16 (butanediyl-1,4-bis(dodecyldimethylammonium bromide) or butanediyl-1,4-bis(hexadecyldimethylammonium bromide)). Small-angle neutron scattering (SANS) studies revealed that in general the initial nonirradiated mixed systems form vesicle-type aggregates (100−200 Å radius), in equilibrium with some smaller charged spheroidal or ellipsoidal micelles (∼20 Å radius). In all cases, UV irradiation resulted in disruption of these vesicles and the formation of charged micelles. 1H NMR showed that the main photoproduct is the cis, anti, cis dimer of E-SGP (ZEZ-DiSGP); hence, photochemically induced changes in the reactive SGP drive significant changes in the preferred aggregation structure. These results demonstrate the utility of photoactive surfactants in mixtures with inert analogues.