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Aggregation behavior and micellar dynamics in aqueous solutions of the nonionic surfactant pentaoxyethyleneglycol monooctyl ether: Effect of sodium halides

1991; Elsevier BV; Volume: 144; Issue: 2 Linguagem: Inglês

10.1016/0021-9797(91)90410-a

1095-7103

W. Binana-Limbelé, N.M. van Os, L.A.M. Rupert, R. Zana,

Photochemistry and Electron Transfer Studies

The aggregation behavior of pentaoxyethyleneglycol monooctyl ether (C8E5) in aqueous solution and some aspects of the dynamics of the C8E5 micelles have been investigated in the absence of added salt and in the presence of sodium halides, as a function of surfactant concentration,C (0.05 to 0.2M), and temperature,T (2–50°C), by time-resolved fluorescence quenching. Some measurements of cloud temperature,Tc, also have been performed. Both in the absence and in the presence of salt it has been found that the micelle aggregation number,N, increases slowly withT at temperatures belowTc −40°C, then increases more rapidly atT> Tc −40°C. The presence of salt amplifies the increase ofN withT. It has been found thatN is mainly determined byTc − T. Thus allN values for the 0.1M C8E5 solutions in the presence of salt fall on a single curve when plotted versusTc − T, irrespective of the nature and concentration of the added salt. As for other nonionic surfactants, a rapid intermicellar migration of probe and quencher has been evidenced atT> Tc − 40°C. This process has been confirmed to take place through collisions among micelles with temporary merging of the collided micelles. The rate constantKe for this process increases withT and with the concentration of added salt, that is, in both instances, upon decreasingTc − T. In the course of this work a peculiar behavior was noted when NaI was added to C8E5 solutions and this behavior was interpreted in terms of the formation of I3 catalyzed by H+, in close proximity to the polyoxyethylene moieties of the surfactant micelles.