Network-forming materials are ubiquitous and appear in industrial products such as tires, food and cosmetics as well as composing the cytoskeleton within the cells of living organisms. They are lightweight and display properties such as optical transparency and reversible deformability up to large strains. However, microscopic mechanisms protecting a network against macroscopic fracture and the processes that control crack growth are still poorly understood. A deeper understanding is needed to fully exploit the potential of polymer networks in advanced and novel material design. To this end, we adapt photon correlation imaging [1] (PCI) to reveal the microscopic rearrangements within poly(ethyl acrylate) networks [2] during deformation by extension and fracture. PCI creates a time-resolved macroscopic map (field of view of several mm) of the microscopic movements (on the order of 1µm) induced by the applied strain preceding fracture. We find that, in our nearly transparent samples, surface scattering dominates the PCI signal, obscuring bulk rearrangements. To address this issue, we first minimise surface scattering by immersing the sample in a pool filled with refractive index matching glycerol, where the geometry of the pool walls is carefully designed to avoid reflections. Furthermore, the pool design allows PCI to be performed at both high (176o) and low (4o) angles simultaneously to measure rearrangements of the polymer network on length scales of 200 nm and 5 µm, respectively. Second, we introduce melamine formaldehyde nanoparticles to the polymer networks to increase the scattering from the bulk. Preliminary measurements reveal non-affine contributions even at low strain, well within the linear regime. We will continue by investigating the role that network architecture, such as interpenetrated multiple networks [3,4], has in the dynamic response of the network and the resultant resistance to fracture. References: [1] A. Duri, D. A. Sessoms, V. Trappe, and L. Cipelletti Phys. Rev. Lett., 2009 102(8), 085702.[2] P. Millereau, E. Ducrot, J. M. Clough, M. E. Wiseman, H. R. Brown, R. P. Sijbesma, and C. Creton, PNAS, 2018 115(37), 9110–9115.[3] J. P. Gong, Y. Katsuyama, T. Kurokawa, and Y. Osada Adv. Mater., 2003 15, 1155. [4] E. Ducrot, Y. Chen, M. Bulters, R. P. Sijbesma, and C. Creton Science, 2014 344, 186.
