Identification of the formation of aggregates in PEO solutions

The properties of poly(ethylene oxide) PEO chains (molecular weight M-W: 65 00) have been examined in dilute solutions in methanol using static (SLS) a nd dynamic (DLS) light scattering. The ability of PEO chains to aggregate d epends on the history of the sample. Thus two relaxation times have been ob served in the correlation functions of the intensity of the light scattered by PEO in methanol when the sample was previously dissolved in hot water ( t greater than or equal to 60 degrees C). The fast mode is attributed to th e well-solvated monomolecular species and the slow mode is because of the f ormation of aggregates that are generated by hydrophobic interactions. Thes e aggregates are well defined, relatively monodisperse and very stable. No aggregation is observed for PEO in methanol when the sample has been previo usly dissolved in a lot of solvents such as water (t = 30 degrees C), chlor oform, dioxane, dimethylsulfoxyde (DMSO), dimethylformamide (DMF) or aceton itrile. (C) 1999 Elsevier Science Ltd. All rights reserved.