Standardized Metrics for Polydimethylsiloxane Bonding: Rupture Pressure-Stress Correlation in Air Plasma-Activated Interfaces.

Reliable and robust bonding of PDMS interfaces is essential for performing microfluidic and flexible electronic devices, where surface activation governs interfacial bonding. This study introduces a geometry-correlated scaling function that converts rupture pressure into maximum von Mises stress at the bonding interface, a threshold as a material property for a given interface, enabling a standardized cross-platform evaluation of bonding strength. Using this material threshold-based framework, we assess the efficacy of air plasma treatment through hydrophilicity measurements, adhesion testing, rupture experiments, and thermal postbonding treatment. Postbonding incubation enables interfacial stresses of 60-120 psi (414-827 kPa), comparable to the published results of oxygen plasma bonding. The strain energy release rate (SERR) of 0.02-0.07 in-lbf/in2 (3.5-12.3 J/m2), while below typical fracture energies, is consistent with the nonasymptotic nature of the rupture configuration. Aging studies show that mild air plasma exposure supports stable long-term bonding. These results show air plasma as a feasible alternative to oxygen plasma and provide a transferable protocol for consistent, interfacial rupture stress-based evaluation of the interfacial bonding performance across platforms.