Surface Modification of ZrO(2) Nanoparticles with TEOS to Prepare Transparent ZrO(2)@SiO(2)-PDMS Nanocomposite Films with Adjustable Refractive Indices

Here, highly transparent nanocomposite films with an adjustable refractive index were fabricated through stable dispersion of ZrO(2) (n = 2.16) nanoparticles (NPs) subjected to surface modification with SiO(2) (n = 1.46) in polydimethylsiloxane (PDMS) (n = 1.42) using the Stöber method. ZrO(2) NPs (13.7 nm) were synthesized using conventional hydrothermal synthesis, and their surface modification with SiO(2) (ZrO(2)@SiO(2) NPs) was controlled by varying the reaction time (3–54 h). The surface modification of the NPs was characterized using Fourier-transform infrared spectroscopy, dynamic light scattering, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and ellipsometry. The surface modification was monitored, and the effective layer thickness of SiO(2) varied from 0.1 nm to 4.2 nm. The effective refractive index of the ZrO(2)@SiO(2) NPs at λ = 633 nm was gradually reduced from 2.16 to 1.63. The 100 nm nanocomposite film was prepared by spin-coating the dispersion of ZrO(2)@SiO(2) NPs in PDMS on the coverslip. The nanocomposite film prepared using ZrO(2)@SiO(2) NPs with a reaction time of 18 h (ZrO(2)@SiO(2)-18h-PDMS) exhibited excellent optical transparency (T(average) = 91.1%), close to the transparency of the coverslip (T(average) = 91.4%) in the visible range, and an adjustable refractive index (n = 1.42–1.60) as the NP content in the film increased from 0 to 50.0 wt%.