Suspensions of modified TiO2 nanoparticles with supreme UV filtering ability

TiO2 nanoparticles (20-23 nm in size) were coated with a silica layer onto which lauric acid was strongly bound. The strong (probably covalent) bonding was proved using detailed comparative thermal analysis. The functionalized TiO2 nanoparticles exhibited significantly reduced agglomeration, both in dry and in dispersed states (in oily media). The reduced tendency towards agglomeration was consistent with contact angle measurements which showed an increased hydrophobicity of functionalized TiO2. The strong (covalent) bonding also greatly improved the stability of the nanoparticulate sample in suspensions. Finally, the UV filtering efficiency of functionalized samples was much improved when compared to non-functionalized or those functionalized using conventional stabilizers based on adsorption. This effect was consistent with our theoretical prediction in which we correlated the particle size and the UV filtering ability.