CONTROLLING THE REFRACTIVE INDEX OF EPOXY ADHESIVES
John M. Messinger, & Peter T. Lansbury
THE NEED FOR MATCHING THE REFRACTIVE INDEX of a mending adhesive to that of a broken glass object has been noted elsewhere.1,2 In an ideal world, this need could be met with a two-component adhesive system, one component of a very high refractive index and the other component of a very low refractive index. Mixing any ratio of the two components would yield an excellent glass adhesive, with the added bonus of creating an adhesive with a refractive index somewhere between the two components and dependent only on the relative amounts of each. Thus, the refractive index of the adhesive mixture could be tailored to that of the glass. Unfortunately, this adhesive system does not yet exist.
The purpose of this study was to find a compound with a very high refractive index that can be added to commercially available, two part epoxy adhesives with lower refractive indices, thereby raising the refractive index of the cured adhesive. Using this three component adhesive system (resin, hardener, and high refractive index additive), a mixture with a refractive index matching that of a cracked piece of glass might thus be obtained by varying the ratio of additive to epoxy resin.