Ref HAL: hal-01580200_v2
Ref Arxiv: 1811.08753
DOI: 10.1021/acs.langmuir.7b01199
WoS: WOS:000405536100019
Ref. & Cit.: NASA ADS
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28 Citations
Résumé:

We study the swelling and shrinking behavior of core-shell microgels adsorbed on silicon wafers. In these systems, the core is made of cross-linked poly(N isopropylmethacrylamide) and the shell consists of cross linked poly(N-n propylacrylamide). In suspension, these particles exhibit an extended linear swelling behavior in the temperature interval between the lower critical solution temperatures of the two polymers. Using ellipsometry and AFM, we show that this linear response is also observed in the adsorbed state.

Ref HAL: hal-01580193_v1
DOI: 10.1021/acs.macromol.7b00954
WoS: WOS:000405642700029
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12 Citations
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The microstructure of polymer nanocomposites made with disordered silica filler (Zeosil(R) 1165MP) of industrial relevance and various coating agents is quantitatively analyzed using a combination of SAXS, TEM, and a recently developed structural model. The polymer matrix is formed by an end-functionalized styrene-butadiene statistical copolymer capable of covalent grafting on the silica nanoparticles. The effect of the coating agents with different alkyl chain length (C8, C12, and C18) on filler structure quantified in terms of aggregate formation, for different concentrations (up to 8%wt with respect to silica), and the effect of a commonly added catalyzer, DPG, are studied using the structural model. As a result we show that a strongly synergetic effect of both DPG and coating agent exist. Our findings open the road to a fundamental understanding and rational design of model and industrial nanocomposite formulation with optimized coating agents.

Ref HAL: hal-01574850_v1
DOI: 10.1039/c6cp06475b
WoS: WOS:000394940400044
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2 Citations
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Gene therapy is based on nucleic acid delivery to pathogenic cells in order to modulate their gene expression. The most used non viral vectors are lipid-based nanoaggregates, which are safer than viral carriers and have been shown to assemble easily with both DNA and RNA. However, the transfection efficiency of non viral carriers still needs to be improved before intensive practise in clinical trials can be implemented. For this purpose the in depth characterization of the complexes formed by nucleic acids and their transporters is of great relevance. In particular, information on the structure and assembly mechanism can be useful to improve our general knowledge of the se artificial transfection agents. In this paper the complexation mechanism of short interfering RNA and DNA molecules (siRNA and siDNA, respectively) with cationic micelles are investigated by combining Small Angle X-Ray Scattering experiments and Molecular Dynamics simulations. Micelles were obtained by Gemini surfactants with different spacer length (12-3-12, 12-6-12). The siRNA and siDNA used were double strand molecules characterized by the same length and homologous sequence, in order to perform close comparison. We showed that complexes appear in solution immediately after mixing and, therefore, the investigation of complex formation requires fast experimental techniques, such as stopped-flow synchrotron SAXS. The obtained systems had internal arrangement constituted by layers of squeezed micelles alternating the nucleic acids. Both SAXS and MD analysis allowed to evaluate the mean size of complexes in the range of few nanometers, with looser and less ordered stacking for the DNA containing aggregates.

Ref HAL: hal-01552103_v1
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Ref HAL: hal-01552100_v1
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Small-angle scattering is a powerful and popular technique for the characterization of the average structure of dense nanoparticle assemblies and aggregates. It is usually limited to not too big assemblies due to the limited q-range, and low enough concentrations to avoid interactions. A straightforward and quantitative analysis of the generally available scattered intensity – even for large assemblies, at high concentrations – at intermediate-q is detailed. It is based on the similarity in local structure between infinitely large homogeneous assemblies of hard spheres or moderately sticky hard spheres with any finite-sized nanoparticle assembly dominated by hard sphere interactions. The method provides information on the local volume fraction of particles. The approach is then extended to polydispersities up to 40%, using numerical simulations of hard spheres and mildly sticky hard spheres. As a result, a simple relationship between the observed structure factor minimum – termed the correlation hole – and the local volume fraction on the scale of neighboring particles, which is also linked to the coordination number, is given. This relationship shall be useful as a simple and efficient tool for the structural analysis of arbitrary aggregated colloidal systems. Finally, recent examples of filler structure in model and industrial polymer nanocomposites will be reviewed.

Ref HAL: hal-01552098_v1
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Polymer nanocomposites are mixtures of nanoparticles and polymer chains, where the filler particles are usually added to enhance mechanical properties, e.g. of car tire materials. Performance depends to a great extent on the structure of the filler, i.e. its dispersion state in the polymer matrix, which itself depends on mixing protocols, but also on the thermodynamics of the system. The latter can be tuned by performing either chemical surface modifications of the nanoparticles, or by playing with the mass and/or grafting properties of the polymer chains. Some straightforward ways to obtain information from small-angle scattering on the filler structure of nanocomposites will be presented. In particular, we recently developed a quantitative analysis of the scattered intensity in the intermediate q range. It is based on the similarity in local structure between infinitely large homogeneous assemblies of hard spheres or moderately sticky hard spheres with any finite-sized nanoparticle assembly dominated by hard sphere interactions. This method provides direct information on the local volume fraction of particles. It will then be applied to the impact of small molecules on the silica structure in nanocomposites close to industrial applications.Finally, a second issue for the mechanical response of nanocomposites relates to the polymer dynamics, which may also be governed by the filler dispersion. We will present first quasi-elastic neutron scattering results showing the impact of the aggregation state on the segmental dynamics of the same samples by means of incoherent neutron spin-echo.

Ref HAL: hal-01548255_v1
DOI: 10.1038/s41598-017-04271-x
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Nowadays powerful X-ray sources like synchrotrons and free-electron lasers are considered as ultimate tools for probing microscopic properties in materials. However, the correct interpretation of such experiments requires a good understanding on how the beam affects the properties of the sample, knowledge that is currently lacking for intense X-rays. Here we use X-ray photon correlation spectroscopy to probe static and dynamic properties of oxide and metallic glasses. We find that although the structure does not depend on the flux, strong fluxes do induce a non-trivial microscopic motion in oxide glasses, whereas no such dependence is found for metallic glasses. These results show that high fluxes can alter dynamical properties in hard materials, an effect that needs to be considered in the analysis of X-ray data but which also gives novel possibilities to study materials properties since the beam can not only be used to probe the dynamics but also to pump it.