Additive manufacturing of high-performance, flexible 3D siloxane-based scintillators through the sol-gel route

A novel method for the production of high-performing, flexible 3D-printed siloxane-based scintillators is here described. It consists in the synthesis via sol-gel of phenyl-bearing siloxane resins with methacrylate functionalities suitable of photopolymerization by UV illumination, therefore shaped at desired geometries through additive manufacturing, namely digital light processing (DLP). Both hydrolytic and non-hydrolytic sol-gel approaches are adopted to promote the reactivity of diphenyl bearing alkoxysilane precursors and to control phase separation of dimethyl and diphenyl rich domains. The structural evolution during the sol-gel reactions is investigated by Fourier transform infrared spectroscopy (FTIR), which is also exploited to assess photocuring, after addition of diphenyl 2,4,6 trimethyl - benzoyl phosphine oxide (TPO) as UV initiator. The optical properties after addition of suitable fluorophores are studied by excitation/emission spectroscopy. Once defined the best formulations as for optical clarity, mechanical toughness and extent of photocuring, thin disks of scintillators are produced by UV illumination and exposed to α particles to define the light output values. The gathered scintillation light has been compared to the one from standard, non-flexible plastic scintillator EJ-212, resulting in values up to 44%. Photorheology is used to assess the printability by DLP, monitoring UV curing times and complex modulus plateau. Tensile tests are performed aiming to observe the stress-deformation behaviour of representative siloxane-based resins obtained by either simple casting or DLP, to get insight on possible variations induced by the fabrication technology. To assess printing resolution and capabilities, selected formulations of photocurable polysiloxanes scintillators are 3D printed by DLP in forms of benchmark shapes, i.e. gyroid and Kelvin cell, and printing quality is derived by scanning electron microscopy (SEM), while their scintillation upon 4.5 MeV H+ ion beam irradiation is gathered by CCD camera observations, affording beam spot image reconstruction.