Rapid ultraviolet curing of epoxy acrylate films with low refractive index and strong interfacial adhesion

The low refractive index of coatings for optical fiber helps to reduce the information loss in optical transmission. However, previous studies focused on decreasing refractive index by adding fluorine-containing monomers into the curing system, ignoring the effect of the functional monomer on the adhesion of the coating onto the optical fiber. To address this limitation, this paper established a rapid light-curing system that reduced the refractive index of the cured film while enhancing the interfacial adhesion between optical fiber and coatings. Based on the Lorentz equation, the low molar refractive index of fluorine atoms was utilized to reduce the refractive index of the light-cured films. Simultaneously, the bisphenol A epoxy acrylate, as an oligomeric main resin, was highly active in cationic photoreaction and can effectively enhance interfacial adhesion. Moreover, the methyl methacrylate was applied to increase the compatibility of epoxy resins and fluorine-containing monomers. The experimental data indicated that the refractive indices of the cured films with fluorine-containing monomers were adjustable from 1.4930 to 1.5576, and the light transmittance was greater than 90%. The curing rate of the sample containing 11.3 wt% of fluorine (F-11.3%) was 26.26 J∙cm−2, which was 28.6% higher compared to that without fluorine. Intriguingly, in terms of molecular dynamics simulations, the interfacial interaction between fluorine-containing monomers and SiO2 crystalline surfaces was modeled. As a result, the interfacial energy between the curing system F-11.3% and SiO2 was −1879.91 kcal/mol, which was 1.16 times higher compared with the cured system without trifluoromethyl methacrylate, proving that increasing the fluorine content is profitable to promote the adhesion force in this system. This paper provided a design method of optical fiber coatings with strong interfacial adhesion, low refractive index and rapid light curing.