The stress‒strain behavior of poly(methyl acrylate) microparticle-based polymers determined via optical microscopy

The structural integrity of microparticle-based films is maintained through interpenetration of the superficial polymer chains of the microparticles that physically crosslink neighboring microparticles. This structural feature is fundamentally different from those of conventional polymers prepared by solvent casting or bulk polymerization. To understand the mechanical properties of such microparticle-based films, it is necessary to investigate the behavior of their constituent particles. However, methods are still being developed to evaluate microscale structural changes in microparticle-based films during the stretching process leading to film fracture. In this study, we propose a method that combines a stretching stage with optical microscopy to investigate the changes in particle morphology and its positional relationship with surrounding particles during uniaxial tensile tests on microparticle-based films. In a film consisting of cross-linked poly(methyl acrylate) microparticles, the deformation of the particles deviated from affine deformation due to the cross-linked structure. However, the deformation of a group of several (local) particles was confirmed to be location-dependent and larger than that of each particle forming the film. The method established here can be used to contribute to the design of tough microparticle-based films.