Gap Filling Optical Adhesives/Epoxies
"I need an epoxy to join two BK7 glass parts together. Gap is around 0.2mm. Light will cross the interface. Reasonable index match to the glass required. Low stress/shrinkage so it doesn’t distort the parts please. Viscosity not too runny, as we want it to stay in place prior to cure."
Optical glass-bonding adhesives are available that have good adhesion to BK7 Glass, a close refractive-index match to the glass, low shrinkage (low modulus), and moderate viscosity to avoid running. Light-curable adhesives like OP-29, which is a one-part adhesive from DYMAX, are available exclusively through Fiber Optic Center. FOC also carries various 2 two-part epoxies or 1 one-part frozen epoxies which should meet your requirements. An alternative source would be to visit the Edmund Scientific website and review their adhesive selections. Epotek 353-ND and 353-T epoxy are also widely used in the glass-bonding/optical adhesives market.