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"Hairy" nanoparticles (HNPs), i.e. inorganic NPs functionalized with polymer chains, are promising building blocks for the synthesis of advanced nanocomposite (NC) materials having several technological applications. Recent evidence shows that HNPs self-organize in a variety of anisotropic structures, resulting in an improvement of the functional properties of the materials, in which are embedded. In this paper, we propose a three-step colloidal synthesis of spherical SiO2-HNPs, with controlled particle morphology and surface chemistry. In detail, the SiO2 core, synthesized by a modified Stöber method, was first functionalized with a short-chain amino-silane, which acts as an anchor, and then covered by maleated polybutadiene (PB), a rubbery polymer having low glass transition temperature, rarely considered until now. An extensive investigation by a multi-technique analysis demonstrates that the synthesis of SiO2-HNPs is simple, scalable, and potentially applicable to different kind of NPs and polymers. Morphological analysis shows the overall distribution of SiO2-HNPs with a certain degree of spatial organization, suggesting that the polymer coating induces a modification of NP-NP interactions. The role of the surface PB brushes in influencing the special arrangement of SiO2-HNPs was observed also in cis-1,4-polybutadiene (cis-PB), since the resulting NC exhibited the particle packing in "string-like" superstructures. This confirms the tendency of SiO2-HNPs to self-assemble and create alternative structures in polymer NCs, which may impart them peculiar functional properties.

Silica–natural rubber nanocomposites were obtained through a novel non-aqueous in situ sol–gel synthesis, producing the amount of water necessary to induce the hydrolysis and condensation of a tetraethoxysilane precursor by esterification of formic acid with ethanol. The method allows the synthesis of low hydrophilic silica nanoparticles with ethoxy groups linked to the silica surface which enable the filler to be more dispersible in the hydrophobic rubber. Thus, high loaded silica composites (75 phr, parts per hundred rubber) were obtained without using any coupling agent. Transmission Electron Microscopy (TEM) showed that the silica nanoparticles are surrounded by rubber layers, which lower the direct interparticle contact in the filler–filler interaction. At the lowest silica loading (up to 30 phr) silica particles are isolated in rubber and only at a large amount of filler (>60 phr) the interparticle distances decrease and a continuous percolative network, connected by thin polymer films, forms throughout the matrix. The dynamic-mechanical properties confirm that the strong reinforcement of the rubber composites is related to the network formation at high loading. Both the improvement of the particle dispersion and the enhancement of the silica loading are peculiar to the non-aqueous synthesis approach, making the method potentially interesting for the production of high-loaded silica–polymer nanocomposites.

Silica-rubber nanocomposites were obtained by in situ sol-gel synthesis, using trialkoxysilanes with different functional groups as precursors. The functionalities were selected in order to favor the formation of differently shaped silica particles and/or to modulate the filler-filler and the filler-rubber interactions. The functional groups included (a) alkyl and alkenyl groups: triethoxy(vinyl) (VTEOS), triethoxy(propyl) (PTEOS), triethoxy (octyl) (OCTEOS); (b) N-containing alkyl groups: triethoxy(3-aminopropyl) (APTEOS), triethoxy(3- cyanopropyl) (CPTEOS), triethoxy(3-propylisocyanate) (ICPTEOS); (c) S-containing alkyl groups: trimethoxy(3-mercaptopropyl) (TMSPM), bis(3-triethoxysilylpropyl) disulfide (TESPD), bis(3-triethoxysilylpropyl) tetrasulfide (TESPT); triethoxy(3-octanoylthio-1-propyl) (NXT). Transmission electron microscopy (TEM) investigation suggested a relationship between the morphology of the filler network and the used trialkoxysilanes, as a function of the particle shape and of the interaction of the particle surface groups between them and with the matrix. The dynamic-mechanical properties of nanocomposites, both uncured and vulcanized, were discussed in relation to the network morphology, suggesting a connection between the used silica precursors and the functional properties. The filler-rubber interaction due to substituents which chemically interact with the polymer, promotes the homogeneous distribution of the silica particles in the matrix, while the filler-filler interaction, favored by the shape induced physical interactions or by the chemical interaction among surface groups, mainly contribute to the filler networking and to the dynamic-mechanical properties of the composites. © 2013 The Royal Society of Chemistry.