Colloidal silica nanoparticles synthesized from tetraethoxysiliane via a sol–gel process were surface modified by 3-(trimethoxysilyl)propyl methacrylate (MSMA) and 1,1,1,3,3,3-hexamethyldisilazane (HMDS). MSMA acted both as a C=C provider and a coupling agent, whereas HMDS was used to prevent particle aggregation and engender hydrophobicity. The modified silica particles (HMSiO2) were UV-cured together with the crosslinking agent, dipentaerythritol hexa-acrylate (DPHA) to form coatings on poly(methyl methacrylate) (PMMA) substrates. Dynamic light scattering of the synthesized sols indicated that the average size of HMSiO2 was ca. 10 nm, consistent with that obtained from TEM imaging. FTIR spectroscopic analyses demonstrated chemical attachment of HMDS to the silica particles. The cured coatings were characterized in terms of water contact angle, light transmittance, hardness, abrasion resistance, and surface morphology. It was found that hydrophobicity of the coatings increased while light transmittance and hardness decreased with increasing HMDS content. DPHA played the role of providing mechanical strength and adherence; however, the coatings became lightly hazy when the weight ratio of DPHA/silica fell in the range 0.3–0.7. In the optimal case, a hard coating (4H) with water contact angle of 108° and transmittance of ~100% (vs PMMA) had been obtained at the DPHA content of 10 wt%.
Journal of Coatings Technology and Research 13(6), p.999-1007