Three-dimensional imaging and measurement of the microscale deformation in soft thin films under micro-indentation

Micro-indentation has been used in measuring mechanical properties of soft materials. However, the complex contact mechanics of soft interfaces pose challenges in the accurate characterization of mechanical parameters from conventional measurement methods. In this work, we present an in situ imaging setup capable of measuring three-dimensional (3D) microscale deformation of soft elastic thin films subjected to a microindenter. Combining fluorescent confocal imaging and particle tracking techniques, microscale surface displacement profiles and stress–strain distributions are accurately quantified. Using this technique, we directly compare microscopic deformations in thin soft films with a thickness range, demonstrating the transition from “sink-in” to “pile-up” as the thickness of the film decreases. We also reveal an intricate difference in displacement fields for different lubrication conditions between the microindenter and soft thin film. These results demonstrate the capacity of our experimental setup as a powerful tool in understanding the unique micro-mechanical behaviors of various soft materials.