Aggregation behavior of α,ω-type nonionic surfactant in aqueous solution

Abstract

Aqueous micellar solutions of α,ω-type nonionic surfactants, dodecanediyl-1,12-bis(tris(oxyethylene) monoether) (C 122E 3) and dodecanediyl-1,12-bis(tetrakis(oxyethylene) monoether) (C 122E 4) have been investigated as a function of temperature and concentration by static and dynamic light scattering and time-resolved fluorescence quenching. The lower consolution temperatures ( T c ) of these nonionic surfactants are almost the same as those of unipolar poly (oxyethylene) surfactants such as C 12E 6 and C 12E 8, while their critical concentrations are close to those of unipolar surfactants which have the same head group and an alkyl chain half as long. The aggregation number and micellar size of C 122E 3 increase more sharply with concentration than those of C 122E 4. Below T = T c − 35°C, the micellar size increases little with temperature. However, above T = T c − 35°C the micellar size increases rapidly with temperature for both surfactants. The increase of micelle size and aggregation number with temperature in C 122E 3 is more pronounced than in C 122E 4. Comparison of the aggregation numbers m obtained from light scattering and fluorescence quenching clearly reveals the occurrence of attractive intermicellar interactions, particularly in C 122E 3 solutions, which prevent accurate determination of the aggregation number by light scattering at high concentration or temperature in the range between T c − 35°C and T c . Debye plots at increasing temperature show that for C 122E 4 the intermicellar interactions become attractive at T > 35° C. Fluorescence quenching data provide evidence of a small micelle polydispersity in the range where the intermicellar interactions become attractive. Some information on the micellar dynamics has also been obtained and is reported.