Preparation of optical axial GRIN components through migration of charged amorphous ZrO2 nanoparticles inside an organic–inorganic hybrid matrix by electrophoresis

A novel sol–gel synthesis route for the preparation of a transparent organic–inorganic nanocomposite was developed by combining methacrylic acid (MA) stabilized, amorphous ZrO2 nanoparticles, which were synthesized by the sol–gel process, with an organic–inorganic dodecandioldimethacrylate (DDDMA)/3-methacryloxypropyl trimethoxysilane (MPTS) hybrid matrix. The average hydrodynamic particle size was determined to be approximately 6 nm by photon correlation spectroscopy. HR-TEM micrographs present irregular shaped zirconia particles with diameters up to 3 nm. Nearly solvent-free nanocomposites with zirconium (Zr) contents up to 15.2 mol% were synthesized and photochemically cured to transparent crack-free bulks. The surface charged nanoparticles in 1-propanol had an electrophoretic mobility of 0.017 (μm cm)/(V s), measured by Laser Doppler Anemometry (LDA) and a refractive index ne of ⩾1.648 ± 0.007 determined by spectroscopic ellipsometry. After filling the nanocomposite into a linear electrophoresis cell (1 × 1.6 × 0.8 cm3), positively charged high refractive nanoparticles migrated through the low refractive hybrid matrix toward the cathode by the application of an electric potential difference of 2 kV/cm for 96 h. A 67% increase in Zr over a distance of 8 mm between the cathode and anode was observed by high-resolution scanning electron microscopy (HR-SEM) and energy dispersive X-ray spectroscopy (EDXS).