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