Time-dependent heterogeneity in polyacrylic pressure sensitive adhesive

Pressure sensitive adhesive (PSA) consists mainly of tacky polymeric materials that adhere to a solid substrate upon applying a contact pressure and is one of the promising candidates for various future applications. To accelerate the application of PSA, especially to a tiny piece of material, the structure and physical properties at various size scales must be well understood. To that end, we examined local rheological properties of a random copolymer composed of n-butyl acrylate and 2-hydroxyethyl acrylate, poly(BA-r-HEA), which was a representative for polyacrylic PSAs by a particle tracking technique with nanometer-scaled particles of quantum dots (QD) as a probe. The observation for individual QDs at different locations was found to be heterogeneous as the time scale was shorter than the terminal relaxation of poly(BA-r-HEA) chains. Being aware of the appearance and disappearance of the heterogeneity will lead to the optimization of the usage process and the molecular design of PSA with improved performance.