Surface Modification of ZrO2 Nanoparticles with TEOS to Prepare Transparent ZrO2@SiO2-PDMS Nanocomposite Films with Adjustable Refractive Indices

Abstract

Here, highly transparent nanocomposite films with an adjustable refractive index were fabricated through stable dispersion of ZrO2 (n = 2.16) nanoparticles (NPs) subjected to surface modification with SiO2 (n = 1.46) in polydimethylsiloxane (PDMS) (n = 1.42) using the Stöber method. ZrO2 NPs (13.7 nm) were synthesized using conventional hydrothermal synthesis, and their surface modification with SiO2 (ZrO2@SiO2 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 SiO2 varied from 0.1 nm to 4.2 nm. The effective refractive index of the ZrO2@SiO2 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 ZrO2@SiO2 NPs in PDMS on the coverslip. The nanocomposite film prepared using ZrO2@SiO2 NPs with a reaction time of 18 h (ZrO2@SiO2-18h-PDMS) exhibited excellent optical transparency (Taverage = 91.1%), close to the transparency of the coverslip (Taverage = 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%.

Zirconia nanocomposites and their applications as transparent advanced optical materials with high refractive index

“…[29][30][31][32] A suitable EMA model should be selected by comparing the calculated and measured refractive indices, medium uniformity, and NP content in the medium. 33…”

“…[45][46][47][48] SiO 2 is optically transparent and has excellent mechanical, chemical, and thermal stability. 33 SiO 2 layers can be reproducibly formed on ZrO 2 NPs using the sol-gel process, called the Stöber method, with effective controls of the layer thickness in nanometer. 21,43 The commonly used SiO 2 precursors for the solgel method are tetramethoxysilane (TMOS) and [Correction added on 1 April 2023, after first online publication: In the second sentence of section "Surface modification and functionalization of ZrO 2 NPs for THPN applications", the nanomaterials has been updated in this version.]…”

“…Representative EMA models include the Arago–Biot equation, Maxwell–Garnett theory, and Bruggeman model 29–32 . A suitable EMA model should be selected by comparing the calculated and measured refractive indices, medium uniformity, and NP content in the medium 33 …”

“…The surface modification of NPs with SiO 2 layers can be introduced as a simple method to improve NPs dispersion in polymer matrices 45–48 . SiO 2 is optically transparent and has excellent mechanical, chemical, and thermal stability 33 . SiO 2 layers can be reproducibly formed on ZrO 2 NPs using the sol–gel process, called the Stöber method, with effective controls of the layer thickness in nanometer 21,43 .…”

“…Alkoxysilane‐capped NPs are advantageous in introducing functional polymer layers on NP surfaces, identical to or chemically compatible with the polymer matrix, and improves the NPs dispersion with consideration of the polymer chemistry. Similar approaches have been applied in fabricating THPN with ZrO 2 @SiO 2 NPs, incorporated into polydimethylsiloxane (PDMS) 33 . Pixelligent Inc. a representative commercial ZrO 2 NPs supplier, has introduced organic layers onto the surface of ZrO 2 NPs to develop ZrO 2 NPs, which have strong chemical affinities with various polymers matrices, such as epoxy, acryl, and siloxane resin 51,52…”