UV-curable epoxy based nanocomposite adhesive for applications in integrated optics

Abstract

UV-curable epoxy based adhesive was filled with nansize SiO2-particles with particle diameters of about 10 nm (SiO2-content in the composite adhesives up to 35 wt.-%). Viscosities of the filled uncured adhesives were kept low at about 1000 mPa-s to 2000 mPa-s by surface modification of the particles. Volume shrinkage rate was reduced from 5.0% (unfilled system) to 3.6 % in the case of a composite material with 20 wt.-% (approx. 12 vol.-%) nanosized SiO2. Hence the coefficient of thermal expansion in a temperature range from -50°C to 100°C, was reduced from 70.10(-6) K-1 to 57.10(-6) K-1. The refractive index decreased from 1.525 to 1.514 at a wavelength of 644 nm. Transmission electron microscopy (TEM) investigations demonstrate that the nanosized SiO2-particles are not agglomerated in the cured material.