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This experimental study of the linear viscoelastic properties of PEG600 aqueous solutions at various concentrations and temperatures mainly aims at getting a better understanding, in concentrated regimes, of the role played on the structural and rheological properties by PEG assembly properties previously evidenced in the dilute regime. The results indicate a peculiar and unique viscoelastic behavior: the elastic modulus versus frequency curves are nearly the same for all concentrations and temperatures investigated. The key role played by hydrogen bonds in the rheological properties of PEG solutions is highlighted. The relaxation on long time scales is indicative of large scale complex associative polymeric structures. A schematic complete phase diagram of PEG600 in water is finally proposed., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The present study was aimed at elucidating the mechanism of aggregation in water of hydroxyl-terminated polyethylene glycol (PEG) of low molecular weight (600 g/mol). The results from fluorescence spectroscopy at different temperatures were consistent with surface tension measurements, suggesting aggregate formation. Indeed, the process of aggregation is accompanied by an increase in the fluorescence emission of a hydrophobic probe. So, PEG aggregates in the form of internal hydrated helices covered with CH(2) groups are shown to yield hydrophobic regions. These regions created upon PEG aggregation in water and at a temperature close to 35°C result from a balance between H bonding and entropic effects. By providing the first experimental evidence for hydrophobic mediation of aggregation with OH-terminated oxy-ethylene chains of low molecular weight, this study highlights their surfactant-like behaviour., (Copyright © 2012 Elsevier Inc. All rights reserved.)

This laboratory study mimicked the pollution of a suspension of silica beads, used as a crude model of sand, by naphthalene in mixture with carbofuran at first, and then by this mixture in association with a metal salt, Pb(NO(3))(2). The silica properties and the working conditions were such that they allowed us to only observe physisorption, which is the first and essential step of any adsorption mechanism. Naphthalene and carbofuran were, respectively, chosen as hydrocarbon and pesticide. Naphthalene adsorption from simple solutions is rather large compared to other organic adsorptions, and carbofuran seems to adsorb on a layer of naphthalene when the latter is mixed in solution with carbofuran. Like other organics, naphthalene favours the adsorption of lead ions, but ionic adsorption is considerably increased by the combination of naphthalene and carbofuran. The Wagner-Onsager-Samaras theory shows that the result implies a special organization of organic molecules at the interface. Conclusions about some environmental mechanisms of fixation, or release, of ions on sands in the case of simple physisorption are drawn from the study., (Copyright © 2010 Elsevier Inc. All rights reserved.)

The behavior of hydroxyl-terminated PEG400 in water was investigated by surface tension measurements and 13C NMR as a function of concentration and temperature. PEG400 exhibited a critical aggregative concentration (cac) that evidenced both its amphiphilic character and its aggregation capacity. Moreover, the chemical shifts of the different carbons of the PEG were followed by NMR versus concentration at various temperatures. We observed a plateau between 20 and 35 degrees C at concentrations above 0.2 mol L(-1) and ascribed it to the aggregation process. A good correlation was found between the NMR spectra in the region of aggregation and the cac region in the phase diagram. Our investigations were also focused on the solid-liquid region of the phase diagram at lower temperatures. These experimental data, together with conclusions available in the literature, led us to propose explanations for the conformation/hydration/aggregation in the PEG400-water solutions phenomena.

This paper presents several studies essentially on the solid/liquid interface. The studied system is the liquid binary mixture water-2,5dimethylpyridine (2,5DMP) in contact with an amorphous silica (Aerosil type). The study of wetting along the two-liquid bulk phases coexistence in contact with silica allows the determination of a wetting transition temperature, which is an important parameter for the adsorption behavior at coexistence. The adsorption isotherms in a diluted phase and in a concentrated phase present some very significant features. In diluted solutions the isotherms show a succession of plateaus; these transitions of layers persist in concentrated phases presenting a sequence of maxima and minima of relative adsorption (Gibbs adsorption) of 2,5DMP with respect to water. In concentrated solutions, they interfere with the prewetting that gives an original shape to the isotherms in concentrated solutions. These adsorption measurements were completed by activity measurements which allow one to obtain the chemical potential of mixtures and linked information. The whole study shows the behavior of colloidal suspensions close to bulk phase changes. Copyright 1998 Academic Press.