In situ generation of CNT/silica hybrid spheres by o/w pickering emulsion templating leads to conductive composite materials with hierarchical porosity

Microcapsules have received considerable attention in various fields, like catalysis, microencapsulation or as smart fillers in nanocomposites for gas sensing. Carbon nanotubes (CNT)-reinforced silica nanocomposites combine the extraordinary strength, hardness, and thermo-chemical stability of the ceramic material with the unique optical, mechanical, and electrical properties of the CNTs and facilitate the percolation of electrically insulator ceramics into electrically conductive composites. The potential applications of CNTs, however, are hindered by their poor dispersibility in most common organic solvents and low interfacial compatibility with ceramic matrices.

We describe here a simple, and effective way of preparing electrically conductive CNT/silica nanohybrid spheres based on the self-assembly of the colloidal particles at the interface between two non-miscible liquids (Pickering emulsion templating). The oil-in-water (o/w) emulsions are stable against coalescence and sedimentation. The emulsion volume fraction was highly dependent of the silica and CNT content and the o/w ratio. There is a point of collapse where emulsification fails. CNTs and silica particles both are located in the interface, as evidenced by confocal laser scanning microscopy. The Pickering emulsions can only be generated in the presence of reactive functional groups at the particles surfaces. (3-Aminopropyl)triethoxysilane is crucial for the formation of the shell structure due to in situ polycondensation with surface hydroxyl groups. It is serving as a binder to fix the nanoparticles at the o/w interface. After drying, hierarchical, open porous structures have been generated. These new nanocomposites are promising as electrically conductive fillers for polymers or ceramics.