Many properties of polymeric systems are determined almost exclusively by the interfaces between various material components. The research in the Illuminating Interfacial Mechanics Lab focuses on the development of novel measurement tools to assess the micromechanical behavior of polymer surfaces and interfaces while observing the resulting deformation with various microscopy techniques. This seminar will focus on the role of interfacial strength on the stress field developed in the matrix of a glass/polymer composite. Here, we utilize a mechanically-activated fluorescent dye molecule (referred to as a mechanophore, MP) to visualize stress gradients that develop around a rigid inclusion upon mechanical deformation. By coupling our experimental observations of mechanophore activation with finite element analysis of the various stress states in the loaded composites, a novel approach to quantitatively calibrate the MP fluorescent activation intensity is established. We then apply our calibration to several test cases of silica/silicone composites with dramatically different levels of interfacial strength and varied geometries. This mechanophore/mechanical deformation approach enables stress fields to be directly observed in a powerful new way via confocal fluorescence imaging in a mechanically loaded polymer composite.