Photorheologic silicone composites with adaptive properties by utilizing light-degradable organosilica nanoparticles as fillers

Implementing inorganic filler particles is a powerful method for improving the mechanical properties of the formed composites. Fillers made of silicon dioxides can be found in countless polymeric materials. Because the interaction of the silica with the polymer determines the physical properties, factors like the surface-to-volume ratio (controlled via the particle size) and surface modification are important. Systems in which the particles are just physically dispersed in the polymer behave significantly differently to those for covalent anchoring of the fillers. Another possible functionality of the filler particles we focus on in the current publication is that they can bring stimuli-responsive properties to the system. Our concept is that photo-degradable organosilica nanoparticles can change the mechanical properties of a polymer/filler composite after it has been prepared. Because of the of the huge applicability of polysiloxanes ranging from building materials to medicine, silicones were selected as the center of interest for the current paper. After the synthesis of organosilica nanoparticles containing a bridging nitrobenzyl ether, and the investigation of the photochemical decomposition processes, the preparation of the composites is described. It is shown that vinyl groups attached to the surfaces are crucial for securing a homogeneous distribution of the filler particles inside the polymer matrix. Finally, the light-induced decomposition of the organosilica is executed and the mechanical properties are investigated by dynamic mechanical analysis. Other than expected, the material becomes stiffer. This effect is explained by a coupled increase of the surface-to-volume ratio of the silica particles accompanied by the emergence of hydroxy groups which interact with the polysiloxane backbone.