The stability of the adhesive layer in cemented prisms under high-temperature conditions directly impacts their optical performance and service life. This is particularly true in precision optical systems, where debonding and deformation caused by thermal expansion, softening, or decomposition can significantly degrade image quality. Improving adhesive layer stability through additives requires three key approaches: inhibiting thermal decomposition, adjusting the thermal expansion coefficient, and enhancing interfacial bonding. This approach is achieved through a combination of molecular design and chemical modification.
Inhibiting thermal decomposition is a core function of additives. Traditional optical adhesives are susceptible to softening or volatilization due to molecular chain breakage at high temperatures. However, silicone pressure-sensitive adhesives, by incorporating cage-type polysilsesquioxanes (POSS) containing unsaturated reactive groups, form a three-dimensional network structure that inhibits thermal decomposition. The nanoscale cage structure of POSS effectively blocks heat transfer, while the high bond energy of its Si-O (452 kJ/mol) improves the thermal stability of the adhesive. Furthermore, the addition of nano-silica (SiO₂) further increases the thermal decomposition temperature, reducing the generation of volatiles at high temperatures and maintaining the structural integrity of the adhesive layer.
Adjusting the thermal expansion coefficient is key to reducing thermal stress. Differences in thermal expansion coefficients between the adhesive layer and optical glass can lead to interfacial delamination at high temperatures. However, the addition of inorganic whiskers (such as silicon nitride whiskers) and silane coupling agents can enhance the compatibility of the adhesive with the glass substrate. Silane coupling agents chemically bond to the whisker surface to form a transition layer, reducing interfacial thermal stress. For example, the addition of a silane-modified polyamide-46 blend allows the adhesive to maintain a thermal expansion coefficient close to that of glass at high temperatures, preventing delamination or cracking caused by thermal stress.
Enhancing interfacial adhesion requires optimizing the adhesive layer structure at the molecular level. Traditional adhesives are prone to debonding at high temperatures due to weak interfacial bonding. Chemical modification can improve adhesion by introducing reactive groups. For example, adding a polyamine curing agent to epoxy resin adhesives creates a denser cross-linked network while also introducing flexible segments (such as polyether segments) to balance rigidity and toughness. These modified adhesives maintain sufficient adhesion at high temperatures while mitigating thermal stress through the flexible segments, preventing brittle fracture.
The molecular design of silicone pressure-sensitive adhesives offers new insights into high-temperature stability. Its backbone is composed of silicon-oxygen bonds, which have a bond energy far higher than the carbon-carbon bonds of traditional acrylic adhesives, making it less susceptible to breakage at high temperatures. The addition of hydrogenated silicone oil and a platinum catalyst enables rapid addition curing without the formation of byproducts, ensuring a pure and non-toxic adhesive layer. Furthermore, the low glass transition temperature (Tg) of silicone silicones (as low as -120°C) enables them to maintain elasticity at low temperatures, preventing brittle cracking and achieving stable bonding over a wide temperature range, from -75°C to 240°C.
Chemical modification technology further expands the application boundaries of additives. For example, microencapsulation technology can encapsulate a repair agent within the adhesive layer. When high temperatures cause cracks, the microcapsules rupture, releasing the repair agent and automatically filling the cracks. This intelligent, responsive additive significantly improves the durability of the adhesive layer in extreme environments. Furthermore, the development of starch-based silicone pressure-sensitive adhesives has enabled biodegradable bonding in the medical field, offering a new direction for environmentally friendly bonding in high-temperature environments.
Improving the high-temperature stability of cemented prism requires the synergistic effects of additives to inhibit thermal decomposition, adjust the thermal expansion coefficient, and enhance interfacial bonding. Molecular design of silicone pressure-sensitive adhesives, modification of POSS and nano-silica, synergistic reinforcement using inorganic whiskers and silane coupling agents, and the development of intelligent, responsive additives have collectively driven breakthroughs in cemented prism's performance under high-temperature conditions. In the future, with advancements in materials science and chemical engineering, the high-temperature resistance of cemented prism will be further enhanced, meeting the demands for extreme environmental adaptability in aerospace, precision instrumentation, and other fields.
