Silica and silicate nanoparticles decorated with guanidinium groups: an innovative platform for the generation of thermoresponsive solvent-free nanofluids

The present study proposes an original approach to obtain silica and silicates decorated with guanidinium groups to be exploited as potential platform for the generation of thermoresponsive solvent-free nanofluids (SFNs). In detail, an alkoxysilane bearing guanidinium functionalities (GuPTES) has been carefully synthesized and then used for the surface functionalization of SiO2 nanoparticles and sepiolite nanofibers, thus generating a positively charged corona layer. Upon careful characterization in terms of grafting density of the silylated guanidinium derivative, the functionalized fillers (SiO2@GuPTES and SepOH@GuPTES) were then modified by a polyethylene glycol provided with anionic sulfonate groups (sulfo-PEG) and acting as canopy, thus obtaining a SFN. The resulting composite materials were characterized by FTIR, TGA, DSC and, particularly, by Time Domain-NMR. Experimental data revealed the presence of structural constraints associated with the formation of ionic interactions between the guanylated surface of the filler and the sulfo PEG group of the polymer chains, which impart temperature-responsive properties, envisaging the promising application of SiO2@GuPTES and SepOH@GuPTES based SFNs as smart solvent-free lubricants.