In situ Synthesis of High Refractive Index PDMS/Metal Oxide Nanocomposites

Abstract

Organic-inorganic hybrids have been prepared with tailorable and enhanced properties which are unachievable using polymers or ceramics alone. By combining the flexibility of polymers with the electronic and optical properties of ceramic materials, these hybrids offer great potential for many optical, electrical and mechanical applications. Silicone polymers because of their desirable surface properties, excellent physical properties, heat stability, and high resistance to chemical and UV attack, have been widely used. Hybrid siloxane-metal oxide gels have been prepared via sol-gel techniques, by using hydroxyl-terminated polydimethylsiloxanes (PDMS) crosslinked by metallic alkoxides, M(OR)n. In this technique, the use of organic solvents permits organic and inorganic components to be combined at a molecular level with the desired composition. By varying the type and percentage of metal alkoxides during synthesis, transparent and homogeneous organic-inorganic hybrid materials with unique properties were obtained. Also a secondary metal oxide species was introduced to synthesize binary metal oxide-PDMS hybrids. Systematic experiments were carried out to study the effect of the reaction conditions and metal alkoxides-PDMS ratios on the properties of the final hybrids. These hybrids were spin coating on silicon wafers or molded into bulk films to be tested. The composition and the properties of the transparent inorganic-organic hybrids were investigated and characterized by ellipsometer and Fourier Transform Infrared (FTIR) spectroscopy. Experimental results showed that the refractive index of the hybrid materials exhibits a proportional relationship with the metal oxide content, the higher the metal oxide content the higher the refractive index. The refractive index was increased from 1.4 of PDMS to 1.7 of metal oxide-PDMS hybrid with highest prepared metal oxide loading. From the FTIR spectra, the structures of the hybrids for various metal oxide-PDMS compositions were examined.

Tuning the Electromechanical Properties of Silicones by Crosslinking Agent

“…These differences cannot influence very much the behaviour of the films. The dilution of the initial mixture with chloroform allows mixing the components at the molecular level, thus creating the premise for a uniform distribution of the hydrolysis‐condensation products of the crosslinker excess within polydimethylsiloxane matrix …”

Structure and Optical Properties of Titania-PDMS Hybrid Nanocomposites Prepared by In Situ Non-Aqueous Synthesis

“…The versatility of the sol-gel chemistry offers wide possibilities for synthesis of organic-inorganic materials with desired contents and nanostructures [ 12 , 13 ]. Hybrid materials based on polydimethylsiloxane (PDMS) have been widely investigated to tune for example the mechanical properties [ 14 , 15 ], the refractive index [ 16 , 17 ] and the hydrophobicity [ 18 , 19 ]. A large family of metal-polydimethylsiloxane nanocomposites (M-PDMS) using metal alkoxides M(OR) z (M = Si, Ti, Zr, Ge, Nb, V, Al, Ta) as precursors have been prepared via various sol-gel approaches [ 14 , 15 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ].…”

“…However, the synthesis required a high pH of 10–13 and two weeks of reaction time. Lu and Mullins [ 16 ] proposed a preparation method in which, contrary to previous methods, no inhibitor nor water was used, greatly simplifying the synthesis of Ti-PMDS materials. The strategy resides in the use of isopropanol as solvent, being also the product of the hydrolysis reaction of titanium(IV) isopropoxide (TIP) and shifting the reaction towards stabilization of the TIP precursor.…”

“…In this work, we extended the sol-gel procedure described by Lu and Mullins [ 16 ] by using different PDMS-OH precursors and various TIP/PDMS-OH molar ratios (i.e., 25 cSt, 50 cSt and 750 cSt and 2:1, 5:1, 10:1, 15:1 and 20:1, respectively) to prepare mould-casted and spin-coated Ti-PDMS hybrid materials. The samples are labelled Ti-PDMS- X - Y :1, where X is the viscosity of the PDMS-OH precursor (in cSt) and Y is the molar ratio of TIP/PDMS-OH.…”

<em>In Situ</em> Synthesis of Hybrid Inorganic-Polymer Nanocomposites

“…More recently, Lu and Mullins [61] used a non-aqueous sol-gel procedure for PDMS-TiO2 nanocomposites. The hydrolysis of TIP was reduced by mixing with isopropanol, before being mixed with PDMS.…”