Model systems of nanocomposites are important for our understanding of the structural and dynamical contributions of the constituents to macroscopic properties, and in particular mechanical reinforcement. Systems in which the filler aggregation can be finely tuned thanks to an aqueous casting route were developed1. The control of the initial colloidal solution stability (mixture of nanolatex and colloidal silica) by the pH enabled to obtain various microstructures for given silica fractions. Using Small Angle Neutron Scattering (SANS) and Transmission Electronic Microscopy (TEM) data, aggregation diagrams were obtained and enabled to study separately the effect of the silica fraction and its aggregation state on mechanical properties2 (see left side of the figure). On the other hand, we studied polymer structure and dynamic in such nanocomposites. SANS experiments were performed on samples prepared with a mixture of hydrogenated (H) and deuterated (D) chains in order to match the silica signal and get independently the polymer signal. A first system made with incompatible H and D latex beads enabled to follow the demixing kinetic for various silica fractions. The evolution of H zone size with annealing indicated that the polymer was immobilized in 15% v silica samples (see right side of the figure)2. A second system made with compatible beads highlighted the dissolution kinetic of latex beads with annealing. With sufficient annealing conditions a molecular mixture of H and D chains was obtained and the effect of silica fraction on chain radius of gyration was studied.

The tunable structure of silica-latex nanocomposites made of silica nanoparticles (radius ≈ 80 Å) and a copolymer of methyl methacrylate and butyl acrylate-latex beads (radius≈210 Å) has been studied by small-angle neutron scattering and transmission electron microscopy. An aggregation diagram as a function of the control parameters--silica volume fraction and precursor solution pH--has been established. In this aggregation diagram, isoaggregation lines have been identified. It was used to express the small-strain reinforcement factor measured with stress-strain isotherms as a function of volume fraction at fixed aggregation number in the range from 50 to 100. The large-strain properties have been rationalized using the energy needed to rupture samples, and this quantity has been found to present an optimum at intermediate volume fractions (15%). In order to understand the striking rheology of the system, a neutron contrast-matching study has been undertaken by adding deuterated polymer beads. The bead demixing kinetics during annealing has been used to characterize the dynamics in various environments defined by the hard silica structure. In particular, in nanocomposite samples containing 15 vol % of silica the dynamics is found to be blocked.

In this paper we used a surfactant-stabilized lyotropic lamellar model system to study the interfacial behaviour of an ion-extracting agent: N1,N3 dimethyl- N1, N3-dibutyl-2-tetradecyl malonamide (DMDBTDMA). An analysis of small angle X-ray scattering (SAXS) and polarized Attenuated Total Reflectance - Fourier Transform Infra Red (ATR-FTIR) data enabled to describe the distribution of the malonamide extractant within the bilayers and its complexation state at the equilibrium. The lamellar phase was diluted with salt water containing varying amount of complexing salt, and each structural state measured was described using a thermodynamic model based on three elementary equilibria: (i) partition of the extractant polar heads between the core and the polar shell of the bilayers, (ii) the complexation of ions by extractants at the bilayers surfaces, and (iii) the partition of bonded extractants between the core and interfaces of bilayers. This model enabled to compare the energy cost of each step.

The infrared spectra of proline rich proteins display a strong band in the 1450 cm-1 region. In the literature, this band was assigned either to the deformation modes of the CH2 and CH3 groups or to the CN stretching mode of proline residues. In order to establish the correct assignment of this band, the impact of proline vibrations in a polypeptide chain is studied and ab-initio calculations are performed for a model molecule (I) containing a repeat unit of polyproline. A strong band is effectively calculated in the 1450 cm-1 region and mostly assigned to CN stretching whereas, due to the absence of N-H bond, there is no amide II band. These results are in good agreement with the spectral features observed in the FTIR spectra of gliadins. Moreover, the spectral shifts calculated when a water molecule is complexed with (I) are consistent with the hydration effect observed in the experimental data.

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In this Letter, we show the benefit of using a lyotropic lamellar phase as a self assembled model system to investigate the distribution of a lipophilic molecule at a hydrophilic/hydrophobic interface. For complexing agents used for ion transfer in liquid/liquid extraction it is essential to determine their interfacial activity. Coupling scattering and spectrometry techniques, we show that it is possible to determine accurately the amount of this type of molecule at the interface.