Synthesis and surface-active properties of new photosensitive surfactants containing the azobenzene group

Several water-soluble cationic surfactants, 4-alkylazobenzene-4'-(oxy-2-hydroxypropyl)trimethylammonium methylsulfate (AZMS) (AZMS-0, AZMS-1, AZMS-2, AZMS-4, and AZMS-8), containing alkylglycidylether and azoarene have been synthesized with high yields of 63-78% and their surface-active properties have been investigated upon irradiation with UV/vis light. All of the trans-AZMS surfactants are isomerized to cis-trans mixtures containing 92.5% cis isomer by UV light irradiation at 350 nm, The cis isomers in the mixtures are reverted to trans isomers by visible light irradiation (lambda > 445 nm). Such photoisomerization induces changes in the surface activity of each surfactant, The critical micelle concentration (cmc) of the trans form of AZMS-8 surfactant is about 1.28 x 10(-4) mol/l, At the photostationary state, 92.5% of the trans form is changed to the cis form which exhibits a slightly higher cmc (3.41 x 10(-4) mol/l). The new cmc of AZMS surfactants upon photoisomerization is similar to that of the ideal mixed micellar system. In particular, the ratio of cmc(cis) to cmc(trans) of AZMS derivatives is about 1.87-2.85 which increases proportionally with the chain length of alkyl group. The minimum average area per molecule (A(min)(a/w)) for the trans and cis isomers of AZMS-8 is 0.60 and 0.74 nm(2), respectively. The difference in the A(min)(a/w) may originate from the structural differences in the two isomers. These values are quite different as compared to those of the conventional azobenzene surfactants, (C) 2000 academic Press.