Rheological characterization of optically clear adhesives using an in situ UV-rheometer: Insights from UV intensities and acrylate monomers

This study investigates the rheological properties of optically clear adhesives (OCAs) commonly used in the display industry, with a focus on the effects of ultraviolet (UV) curing intensity and acrylate monomer composition. Using an in situ UV-rheometer, the research particularly explores the role of isobornyl acrylate (IBOA) in influencing the internal crosslinking structure of OCAs. Results from temperature ramp, creep-recovery, and oscillatory shear tests (SAOS and LAOS) revealed that the incorporation of IBOA leads to higher glass transition temperatures (T_g) of about 30 °C and increased storage modulus (G′) of about 1.1 times, attributed to its bulky molecular structure that limits chain mobility. While I-0 (without IBOA) formed a robust, chemically crosslinked network with solid-like behavior, I-40 (with IBOA) exhibited viscoelastic properties indicative of linear or branched chain structures. These differences were traced to pre-curing chain formation dynamics, where the presence of IBOA and its propagation rate resulted in early crosslinking with shorter chains. The findings provide valuable insights into optimizing UV-curing processes and monomer formulations to tailor OCA performance for advanced display applications.