A new type of transparent scratch resistant coatings including in-situ modified SiO2 （g-SiO2） in flame spray pyrolysis （FSP） process was prepared. The maximum content of g-SiO2 in the coating was 15 wt%, which is higher than that of SiO2 modified by traditional wet chemical route （I-SiO2, only 10 wt%）. The results of transmission electron microscopy have demonstrated that in-situ surface modified g-SiO2 particles dispersed well with smaller agglomerates in the final coating, which was much better than the particles modified via wet chemical route. Visible light transmittance and haze tests were introduced to characterize the optical quality of the films. All coatings were highly transparent with the visible light transmittance of above 80%, especially for coatings containing g-SiO2, which exhibited slightly higher visible light transmittance than l-SiO2 embedded one. The haze value of coatings incorporated with 15 wt% g-SiO2 was 1.85%, even lower than the coating with 5 wt% I-SiO2 （haze value of 2.09%）, indicating much better clarity of g-SiO2. The excellent optical property of g-SiO2 filled coatings was attributed to the good dispersion and distribution of particles. Nano-indention and nano-scratch tests were con- ducted to investigate the scratch resistance of coatings on nano-scale. The surface hardness of the coatings rose by 18% and 14%, and the average friction coefficient decreased by 15% and 11%, respectively, compared to the neat coat due to the addition of 10 wt% g-SiO2 and I-SiO2. The pencil hardness of the coating with 15 wt% g-SiO2 increased from 2B for the neat coating to 2H. However, the pencil hardness of coating with 10 wt% I-SiO2 was only H. The results showed that the g-SiO2 embedded coatings exhibited higher scratch resistance and better optical properties.
Hydrophobic silica nanoparticles grafted with a high amount of organic molecules were successfully pre- pared by an in situ functionalization method in flame spray pyrolysis （FSP） process. Hydrophilic SiO2 nanoparticles were converted into hydrophobic ones by silylation between 3-methacryloxypropyltrimethoxyl silane （MPS） and silica＇s surface hydroxyl groups. The freshly formed silica nanoparticles in flame were continuously functionalized by a fine spray of 3-methacryloxypropyltrimethoxyl silane （MPS） solution at a preferred temperature. The functionalization extent, morphology structure and size of silica nanoparticles were characterized by transmission electron microscopy （TEM）, Brunauer-Emmett- Teller （BET）, thermogravimetric analysis （TGA）, Fourier transform infrared spectroscopy （FT-IR） and X-ray photoelectronic spectroscopy （XPS）. The influence of concentration, pH value and pre-activation of organic silane solution on the surface grafting density was investigated in detail. The obtained silica nanoparticles had a higher MPS functional content of 15.0 wt% （an average density of 2.7 MPS molecule/nm^2） than that of the silica modified by wet chemistry route, showing an excellent, stable hydrophobic property. The results have demonstrated that the in situ FSP functionalization process is a simple, effective and prom- ising route for the scalable preparation of advanced, hydrophobic nanomaterials.
