Spatial-temporal dynamics at the interface of 3D printed photocurable nanocomposite layers

Additive manufacturing (AM) is used to fabricate polymeric materials into complex three-dimensional (3D) structures. As the 3D structure is built by sequential layer-by-layer deposition of filaments dispensed from a translating nozzle, defects often form at the filament-filament interface. The out-of-equilibrium structural development that occurs during the printing process is difficult to directly measure by quantitative means, limiting our understanding of the physical mechanisms at play. Here, we utilize in-operando X-ray photon correlation spectroscopy (XPCS) measurements with microbeam capability to probe the real-time structural evolution at the filament-filament interface during extrusion 3D printing. We investigate the solidification of a dual cure (UV/thermal) acrylate/epoxy resin during multilayer 3D printing as a rational model by tracking the nanoscale motion of filler particles ("tracers") embedded in the polymer matrix. The spatially and temporally resolved dynamics are measured during the deposition of a single filament as well as during the deposition of a second layer on top of the cured underlayer. The XPCS microrheology approach provides insight into the nanoscale mechanisms that dictate the interfacial crosslinking process between printed filaments and progresses towards overcoming the barriers limiting industrial use of extrusion-based AM.