Viscoelastic deformation during thermal cycling of adhesively bonded optical coatings
Temperature-dependent structural deformation in bonded optical materials and dielectric layers has been investigated. Structures of silicon, zinc sulfide, and diamond disks bonded to each other by a thin film of thermoplastic wax adhesive have undergone low-temperature thermal cycling in order to simulate service environments. The deformation, which may adversely affect optical properties of sensitive optical coatings, was measured as a function of temperature and time. An expected amount of elastic deformation due to thermal stresses was numerically modeled for the structures and compared to the actual observed behavior. At temperatures greater than an elastic/inelastic threshold of the adhesive layer, an irreversible deformation within all structures was observed in which the deformation deviated from the numerical elastic model. The viscoelastic behavior within the adhesive film proved to have a significant effect on the deformation of the structure and would consequently affect the optical properties of the device.
Madras, C., Wong, P., & Miaoulis, I. (1996). Viscoelastic deformation during thermal cycling of adhesively bonded optical coatings. Materials Letters, 28 (1-3), 21-26. https://doi.org/10.1016/0167-577X(96)00030-4