We study the phase behavior in water of a mixture of natural long chain fatty acids (FAM) in association with ethylenediamine (EDA) and report a rich polymorphism depending on the composition. At a fixed EDA/FAM molar ratio, we observe upon dilution a succession of organized phases going from a lamellar phase to a hexagonal phase and, finally, to cylindrical micelles. The phase structure is established using polarizing microscopy, SAXS, and SANS. Interestingly, in the lamellar phase domain, we observe the presence of defects upon dilution, which SAXS shows to correspond to intrabilayer correlations. NMR and FF-TEM techniques suggest that these defects are related to an increase in the spontaneous curvature of the molecule monolayers in the lamellae. ATR-FTIR spectroscopy was also used to investigate the degree of ionization within these assemblies. The successive morphological transitions are discussed with regards to possible molecular mechanisms, in which the interaction between the acid surfactant and the amine counterion plays the leading role.
In polymer nanocomposites, particle-polymer interactions play a key role both in the processing and in the final properties of the obtained materials. Specifically, for silica, due to the surface polarity, surface modification is commonly used to improve the compatibility with apolar polymer matrices, in order to prevent agglomeration.In this work, a new way to investigating the polymer-silica affinity and determining dispersibility parameters (HDP) of silica particles in the 3D Hansen space using a solvent approach is proposed. These parameters are estimated from the assessment of the stability of suspensions in a set of organic solvents. Based on the respective locations of the solvent, polymer and silica representative points in the 3D Hansen space, the adsorption of a given polymer in solution in a given solvent can be predicted. This is shown with the industrial precipitated silica Zeosil ® 1165MP in combination with polystyrene and polybutadiene. It is shown that silanization of the silica particles 1 decreases the adsorption of polystyrene, even though due to this surface treatment silica comes closer to polystyrene in the Hansen space. This counter-intuitive effect is rationalized based on the consideration of an adsorption parameter χ S computed from the relative locations of the solvent, polymer and particles in the 3D Hansen space. Basically, this parameter is related to the respective distances of the solvent and polymer representative points to that of the particle in Hansen space.
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