Improving the Durability of Wearable Health Monitors and Flexible Displays
MIE Assistant Professor Ruobing Bai published his research on “Prevalent Low Interfacial Fatigue Threshold in Pressure-Sensitive Adhesives” in the Journal of Applied Mechanics.
Abstract:
The expanding applications of pressure-sensitive adhesives (PSAs) in fields like bioelectronics, healthcare, and flexible displays call for an urgent study on their fatigue behaviors, i.e., damage and fracture under prolonged dynamic loads. However, such studies have been sparse in the field. Here, we show a prevalent low interfacial fatigue threshold in various PSAs through experimental cyclic peeling tests. We characterize interfacial fatigue fracture in PSAs, including the 3M Scotch VHB 4905 tape, the 3M Scotch heavy-duty shipping packaging tape, and two homemade PSAs. The two homemade PSAs consist of different poly(butyl acrylate) elastomeric bulks (low-hysteresis and high-hysteresis) dip-coated with identical viscoelastic poly(butyl acrylate-co-isobornyl acrylate) sticky surface layers. The measured interfacial fatigue thresholds are 3.7 J/m2, 10.8 J/m2, 9.8 J/m2, and 8.1 J/m2 for VHB, packaging tape, low-hysteresis PSA, and high-hysteresis PSA, respectively, all much lower than their bulk adhesion toughnesses at finite crack speeds. The interfacial fatigue threshold agrees qualitatively well with a modified Lake-Thomas model despite an underestimation of the model. However, the measured slow crack threshold in monotonic peeling is larger than the fatigue threshold and shows clear dependence on the bulk dissipation. We discuss possible mechanisms for these discrepancies and potential toughening strategies for PSAs. The new experimental data confirm the prevalence of low interfacial fatigue threshold in PSAs, and further suggest that the threshold is nearly independent of their bulk dissipation.