Janus Nanoparticles by Pickering Emulsions: A Versatile Approach for the Selective Functionalization of SiO ₂

Janus nanoparticles (JNPs) are fascinating colloidal-sized particles characterized by different properties on opposite sides. Among the synthetic approaches, the preparation of JNPs by a masking approach with paraffin wax in water Pickering emulsions appears to be a flexible method for the selective modification of SiO₂ NPs. However, the preparation of JNPs by Pickering emulsions at the nanometric level has yet to be investigated. With the aim of extending the applicability of the method to the modification of nanofillers, commonly employed in polymer composites, the preparation of Pickering emulsions with SiO₂ and paraffin wax has been rationalized. In detail, starting from micrometric silica, a procedure valid for particles of different sizes down to 30 nm was established for the first time. The NPs were functionalized on one hemisphere with (3-aminopropyl)triethoxysilane (APTES), and the resulting APTES-JNPs were further modified with commercially available polymers. The polymer-JNPs show anisotropic characteristics that could impart interesting properties for different applications and could be further modified to create specific building blocks.