Hydrogen-bond driven formation of microstructured pressure sensitive adhesives (PSAs) with enhanced shear resistance

Double-Sided Pressure-Sensitive Adhesive Materials under Human-Centric Extreme Environments

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

Rheological and Mechanical Properties of an Acrylic PSA

The adhesion of pressure-sensitive adhesives (PSAs) is a complex phenomenon that can be understood through the characterization of different properties, including viscoelastic, mechanical, and fracture properties. The aim of the present paper is to determine the viscoelastic behaviour of an acrylic PSA and place it in the viscoelastic window, as well as to determine the tensile strength of the material. Additionally, different numbers of stacked adhesive layers and two crosshead speeds were applied to characterize the tensile strength of the adhesive in the different conditions. Adding a new interface between layers showed a negative influence in the tensile strength, while a higher crosshead speed implied a considerable increase in the same value. Finally, double cantilever beam (DCB) fracture tests were performed, and the J-integral approach was used to evaluate the fracture energy throughout the tests. The substrate roughness, the number of stacked layers, and the thickness of the PSA proved to decrease the performance of the PSA in fracture tests. While tensile bulk tests in viscoelastic materials are not easily found in the literature, as well as DCB tests, for fracture characterization, the obtained results allowed for the characterization of those properties in an acrylic PSA.