The antagonistic effect of processing and thermal annealing on both the filler structure and the polymer matrix is explored in polymer nanocomposites based on natural rubber with precipitated silica incorporated by coagulation from aqueous suspension followed by roll-milling. Their structure and linear and non-linear rheology have been studied, with a particular emphasis on the effect of high temperature thermal treatment and the number of milling passes. Small-angle X-ray scattering intensities show that the silica is organized in small, unbreakable aggregates containing ca. 50 primary nanoparticles, which are reorganized on a larger scale in filler networks percolating at the highest silica contents. As expected, the filler network structure is found to be sensitive to milling, more milling inducing rupture, as evidenced by the decreasing Payne effect. After thermal treatment, the nanocomposite structure is found to be rejuvenated, erasing the effect of the previous milling on the low-strain modulus. In parallel, the dynamics of the samples described by the rheology or the calorimetric glass-transition temperature remain unchanged, whereas the natural latex polymer network structure is modified by milling towards a more fluid-like rheology, and cannot be recovered.

Silica–wollastonite xerogel composites (xerocomposites) with different wollastonite filler content were obtained after classical drying of silica–wollastonite gels. Two different silica precursors were used, TEOS and colloidal LUDOX, for composites named TW and LW, respectively. We utilized SAXS experiments, N2 adsorption–desorption, and SEM techniques to determine the textural and structural properties of these porous materials. For both the TW and LW composites, it was shown that a macroporosity and a mesoporosity coexist. We argue that the proportion of macroporosity directly depends on the proportion of wollastonite fillers in the composite. We propose a unique two-stage drying mechanism to explain the formation of macropores. We additionally found that the surface of wollastonite fillers was covered by a dense multilayer packing of silica colloids in LUDOX LW xerocomposites. We believe that these surface-modified wollastonite fillers could improve the carbonation kinetics of wollastonite when used as a precursor for aqueous mineral carbonation, a promising route for safe and durable carbon sequestration.

Silica-wollastonite xerogel composites (xerocomposites) with different wollastonite filler content were obtained after classical drying of silica-wollastonite gels. Two different silica precursors were used, TEOS and colloidal LUDOX, for composites named TW and LW, respectively. We utilized SAXS experiments, N2 adsorption-desorption, and SEM techniques to determine the textural and structural properties of these porous materials. For both the TW and LW composites, it was shown that a macroporosity and a mesoporosity coexist. We argue that the proportion of macroporosity directly depends on the proportion of wollastonite fillers in the composite. We propose a unique two-stage drying mechanism to explain the formation of macropores. We additionally found that the surface of wollastonite fillers was covered by a dense multilayer packing of silica colloids in LUDOX LW xerocomposites. We believe that these surface-modified wollastonite fillers could improve the carbonation kinetics of wollastonite when used as a precursor for aqueous mineral carbonation, a promising route for safe and durable carbon sequestration.

L’existence d’une phase « Nematique twist Bend » (NTB) a été prédite par I.Dozov dès 2001 [1] mais n’a été observée expérimentalement qu’en 2010 [2]. Cette phase est assez originale car elle présente optiquement des défauts de type coniques focales sans réel ordre translationnel observable en diffusion des rayons X. Généralement cette phase est présente à des températures élevées (au-dessus de 100°C) dans les corps purs. L’ajout d’un nématogène [comme le 4-Cyano-4'-pentylbiphenyl (5CB)] à un composé NTB [tels que le 1,7-bis (4-cyanobiphényl-4-yl) heptane (CB7CB)] permet de diminuer fortement la plage d’existence de la phase NTB [3] tout en modifiant continûment les propriétés thermiques et diélectriques. Dans ce travail, nous avons exploré les modifications dues à l’ajout au CB7CB de smectogènes, et en particulier du 4′-octyl-4-biphénylcarbonitrile (8CB). Le diagramme de phase de ce dernier mélange binaire présente des caractéristiques surprenantes. Malgré leur ressemblance macroscopique, les phases SmA et NTB semblent ainsi incompatibles et restent séparées par une phase nématique s’étendant à très basse température (-20 ° C) pour une fraction CB7CB de ϕ_c≈20%. Nous avons par ailleurs caractérisé les propriétés optiques, thermiques, diélectriques et d’ancrage des phases N et NTB des mélanges. Les propriétés optiques sont très différentes de celles du CB7CB sur une large gamme de composition et de forts effets pré-transitionnels sont observables à l'approche de ϕ_c≈20%. Les propriétés d’ancrage (fig1) sont également significativement modifiées par l'ajout de 8CB au CB7CB ce qui facilite l'alignement homéotrope, très difficilement obtenu pour le CB7CB.

The dynamic and static properties of the interfacial region between polymer and nanoparticles have wide-ranging consequences on performances of nanomaterials. The thickness and density of the static layer are particularly difficult to assess experimentally due to superimposing nanoparticle interactions. Here, we tune the dispersion of silica nanoparticles in nanocomposites by pre-adsorption of polymer layers in the precursor solutions, and by varying the molecular weight of the matrix chains. Nanocomposite structures ranging from ideal dispersion to repulsive order or various degrees of aggregation are generated and observed by small-angle scattering. Pre-adsorbed chains are found to promote ideal dispersion, before desorption in the late stages of nanocomposite formation. The microstructure of the interfacial polymer layer is characterized by detailed modeling of X-ray and neutron scattering. Only in ideally well-dispersed systems a static interfacial layer of reduced polymer density over a thickness of ca. 2 nm is evidenced based on the analysis with a form-free density profile optimized using numerical simulations. This interfacial gradient layer is found to be independent of the thickness of the initially adsorbed polymer, but appears to be generated by out-of-equilibrium packing and folding of the pre-adsorbed layer. The impact of annealing is investigated to study the approach of equilibrium, showing that initially ideally well-dispersed systems adopt a repulsive hard-sphere structure, while the static interfacial layer disappears. This study thus promotes the fundamental understanding of the interplay between effects which are decisive for macroscopic material properties: polymer-mediated interparticle interactions, and particle interfacial effects on surrounding polymer.

Ordered mesoporous silica materials were prepared under different pH conditions by using a silicon alkoxide as a silica source and polyion complex (PIC) micelles as the structure-directing agents. PIC micelles were formed by complexation between a weak poly-acid-containing double-hydrophilic block copolymer, poly(ethylene oxide)-b-poly(acrylic acid) (PEO-b-PAA), and a weak poly-base, oligochitosan-type polyamine. As both the micellization process and the rate of silica condensation are highly dependent on pH, the properties of silica mesostructures can be modulated by changing the pH of the reaction medium. Varying the materials synthesis pH from 4.5 to 7.9 led to 2D-hexagonal, wormlike or lamellar mesostructures, with a varying degree of order. The chemical composition of the as-synthesized hybrid organic/inorganic materials was also found to vary with pH. The structure variations were discussed based on the extent of electrostatic complexing bonds between acrylate and amino functions and on the silica condensation rate as a function of pH.

Aerogels are ultraporous materials with a very low permeability. They exhibithigh specific surface area but, due to their huge porous volume, their mechanical properties are quite poor. Aerogels belong to two main families: inorganic materials as silica, silicates, and a few aluminates and organic aerogels which are easily transformed into carbon aerogels by a simple pyrolysis thermal treatment. In this chapter, we mainly report experiments performed on alcohol-dried aerogels. Due to their broad range of porosity, aerogels canfitin very different applications: from analysis of cosmic dust to nuclear waste containment glasses. Advantages of large porosity are sometimes used directly like in thermal and acoustic insulation, or in catalyzers, but a too high pore volume can also be a drawback like in glass precursor and host matrix. Fortunately, aerogel porosity can be tailored using sintering or room isostatic compression or eventually a combination of both methods. Knowledge in this area allows now to synthesize aerogels with a broad range of porosity and also a very broad range of texture.