Aggregation Behavior of Sugar Surfactants in Aqueous Solutions: Effects of Temperature and the Addition of Nonionic Polymers.
The aggregation behavior, critical micelle concentration (cmc) and micelle aggregation number (N), of dodecyl maltoside (DM), octyl glucoside (OG), and Hecameg has been investigated in water and in water plus one of the three water-soluble polymers, polyoxyethylene (POE), polyoxypropylene (POP), and polyvinyl pyrrolidone (PVP), by means of florescence probing and time-resolved fluorescence quenching. The cmc of DM in water increased with temperature and showed a slight increase in the presence of POE. The aggregation number N of DM micelles was nearly independent of concentration (0.25-1 wt %) and temperature (16-60 degreesC). It remained invariant upon addition of 2 wt % POE or PVP but decreased slightly upon addition of the more hydrophobic POP. With increasing temperature, the cmc of OG decreased, went through a shallow minimum at around 35 degreesC, and increased. Addition of POE slightly increased the cmc in the whole temperature range. The aggregation number of OG micelles showed a fairly flat maximum at around 30 degreesC, and was unaffected by the presence of 2 wt % POE or PVP. However, N showed a complex dependence on temperature in the presence of POP, with lower values than in pure water below 15 degreesC, and rapidly increasing quencher-dependent values above this temperature. Hecameg was characterized by N-values nearly independent of temperature and concentration. Intermicellar exchanges of probe and/or quencher were observed with OG and Hecameg, but not with DM. The above results are compared to those for the nonionic ethoxylated surfactants. The effect of various parameters on the micelle aggregation number, the micelle polydispersity, the occurrence of sugar surfactant/nonionic polymer interactions, and the mechanisms responsible for the observed intermicellar exchanges are discussed. Copyright 1998 Academic Press.
Aoudia
M
Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio, 43403
Zana
R