Double-Sided Pressure-Sensitive\nAdhesive Materials\nunder Human-Centric Extreme Environments

Maintaining the adhesion strength of flexible pressure-sensitive\nadhesives (PSAs) is crucial for advanced applications, such as health\nmonitoring. Sustainable mounting is critical for wearable sensor devices,\nespecially under challenging surroundings such as low and high temperatures\n(e.g., polar regions or deserts), underwater and sweat environments\n(physical activity), and cyclical shear complex stresses. In this\narticle, we consider the adhesive, mechanical, and optical properties\nof medical-grade double-sided PSAs by simulating extreme human-centric\nenvironments. Diverse temperature conditions, water and humidity exposures,\nand cyclical loads were selected and tested over long intervals, up\nto 28 days. We observed that high temperatures increased the shear\nadhesion strength due to the pore closing and expanding contact area\nbetween the adhesive layer and substrate. Conversely, low temperatures\ncaused the adhesive layers to harden and reduce the adhesive strength.\nImmersion in salty and weakly acidic water and excessive humidity\nreduced adhesion as water interfered with the interfacial interactions.\nPSA films showed either adhesive or cohesive failure under extreme\nmechanical stresses and cyclical loading, which is also affected by\nthe presence of various polar solvents. We demonstrated that the variable\nadhesive performance, mechanical properties, and optical transparency\nof pressure-sensitive materials can be directly related to changes\nin their morphologies, surface roughness, swelling state, and alternation\nof the mechanical contact area, helping to establish the broader rules\nof design for wearable human health monitoring sensors for the long-term\napplication of wearable devices, sensors, and electrodes.