Tunable wettability of monodisperse core-shell nano-SiO₂ modified with poly(methylhydrosiloxane) and allyl-poly(ethylene glycol)

In this paper, vinyl-capped silica nanoparticles (V-SiO₂) were first synthesized from tetraethyl orthosilicate (TEOS) and vinyltriethoxysilane (VTEOS). Then the V-SiO₂ nanoparticles were modified with poly(methylhydrosiloxane) (PMHS) and allyl-poly(ethylene glycol) (APEG) to form core-shell hybrid particles V-SiO₂/PMHS/APEG, which showed tunable wettability as well as uniform monodispersity in ethanol and toluene. Particularly, V-SiO₂/PMHS/APEG samples with moderate wettability could be served as emulsion stabilizer for silicone oil-water system. The modified particles were characterized by static contact angle (CA), Fourier transform infrared (FT-IR) spectroscopy, FT-Raman spectroscopy, ²⁹Si CP MAS NMR, thermal analysis (TGA), transmission electron microscopy (TEM) and particle size distribution. FT-IR, FT-Raman and ²⁹Si CP MAS NMR demonstrated that PMHS together with APEG was chemically anchored to the surface of nano-SiO₂. Deduced from static contact angle, strong hydrophobicity (CA=157.76°) could be achieved for V-SiO₂/PMHS particles (m(PMHS):m(V-SiO₂)=1:1), while V-SiO₂/PMHS/APEG samples exhibited moderate wettability (CA=89.20°) when the mass ratio of V-SiO₂, PMHS and APEG was conducted at 1:1:6.0. Thermal analysis (TGA) showed that the grafting yield of PMHS and APEG was 5.76×10^-5 and 6.13×10^-4mol/g, respectively. V-SiO₂/PMHS/APEG samples displayed superior monodispersity in both ethanol and toluene, and the mean diameter was 245.5nm, revealed from particle size distribution. Furthermore, digital photos, optical micrographs and emulsion drop size distribution demonstrated that silicone oil/water emulsions were successfully stabled by the core-shell hybrid particles V-SiO₂/PMHS/APEG.