Michel Duval

Identification of the formation of aggregates in PEO solutions

The properties of poly(ethylene oxide) PEO chains (molecular weight Mw: 6500) have been examined in dilute solutions in methanol using static (SLS) and dynamic (DLS) light scattering. The ability of PEO chains to aggregate depends on the history of the sample. Thus two relaxation times have been observed 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≥60°C). The fast mode is attributed to the well-solvated monomolecular species and the slow mode is because of the formation of aggregates that are generated by hydrophobic interactions. These aggregates are well defined, relatively monodisperse and very stable. No aggregation is observed for PEO in methanol when the sample has been previously dissolved in a lot of solvents such as water (t=30°C), chloroform, dioxane, dimethylsulfoxyde (DMSO), dimethylformamide (DMF) or acetonitrile.

Quasi-elastic light scattering from ternary mixtures of polystyrene/poly(methyl methacrylate)/toluene

The dynamical behaviour of ternary solutions of polystyrene/poly(methyl methacrylate)/toluene has been investigated by quasi-elastic light scattering. Two distinct relaxation modes have been observed in the autocorrelation function of the scattered light. The variation of these modes has been examined as a function of the total polymer concentration C, the relative composition of polystyrene (x = CPSC) and the wavevector q. The experimental results are in good agreement with recent theoretical calculations based on the random-phase approximation. The first mode or the fast one is independent of the composition and characterizes the total concentration fluctuations; it is a cooperative diffusion mode. The second one is sensitive to the composition. It describes the diffusion of one species with respect to the other and is called the interdiffusion mode.

Hydrogenated polystyrene-poly(methyl methacrylate) diblock copolymer micelles in selective solvent: 2. Binary solvent-precipitant mixtures — effect of mixture composition and temperature

Abstract The association of a polystyrene-poly(methyl methacrylate) (PS-PMMA) diblock copolymer in l-chloro-n-hexane/dioxane mixture has been studied by light scattering. A parallel is made between the effect of the addition of precipitant for one block and the decrease of the temperature. As the volume fraction ∅ of precipitant for the PMMA block increases, or at constant ∅ as the temperature T decreases, multimolecular aggregation occurs. Contrary to the degree of association of the molecules, which varies, the dimensions of the micelles are independent of ∅ or T so that the compactness of those micelles increases when ∅ increases or T decreases. At intermediate T or ∅ values, large structures seem to be present in dilute solution.

Hydrogenated polystyrene—poly(methyl methacrylate) diblock copolymer micelles in selective solvent: 1. Single solvent system — effect of temperature

Abstract The association of two block copolymers, hydrogenated polystyrene-poly(methyl methacrylate) (PSH-PMMA) in 1-chloro-n-hexane (a selective solvent for PSH) and deuterated polystyrene-poly(methyl methacrylate) (PSD-PMMA) in dimethyl sulphoxide (a selective solvent for PMMA), has been studied by light and neutron scattering. Unusual large particles are formed in the temperature range corresponding to the theta point of one block of the copolymer whereas small compact micelles are observed at room temperature. At low temperature the results show good agreement with the model of closed association where unassociated molecules are in equilibrium with monodisperse micelles.

STATIC AND DYNAMIC LIGHT SCATTERING FROM MONOFUNCTIONAL IONOMER SOLUTIONS. AGGREGATION OF THE ω-CARBOXYLIC FUNCTIONALIZED POLYSTYRENE THROUGH NEUTRALIZATION IN TETRAHYDROFURAN

A polystyrene (PS), prepared using controlled radical polymerization and fitted at one of its ends by a carboxylic acid function, was neutralized with a manganese acetate salt. The aim of the study was to characterize the neutralized form of this polymer by comparison with the related acid polymer. The study was performed in a solvent with weak polarity, tetrahydrofuran (THF). The elastic and quasi-elastic light-scattering techniques used inform on the static and dynamic behavior of the polymer. Studied concentrations are in the diluted regime (c < c *) of free chains. The elastic light-scattering distribution reported by neutralized chain solutions showed the presence of large-size objects. The intensity autocorrelation function obtained on the quasi-elastically scattered light showed, in the case of the acid form, a simple diffusive relaxation mode; for the manganese-neutralized form, it showed two well-separated diffusive modes. An aggregation occurred between chains, and it was shown that it exists in the weakest concentrations studied (c */60), and that aggregates coexist with unassociated chains in solution. The results obtained are compared with an aggregation model.