  Photopolymerization processes are exploited in light exposure-based 3D
printing technologies, where either a focused laser beam or a patterned light
sheet allows layers of a UV curable, liquid pre-polymer to be solidified. Here
we focus on the crucial, though often neglected, role of the layer thickness on
photopolymerization. The temporal evolution of polymerization reactions
occurring in droplets of acrylate-based oligomers and in photoresist films with
varied thickness is investigated by means of an optical system, which is
specifically designed for in-situ and real-time monitoring. The time needed for
complete curing is found to increase as the polymerization volume is decreased
below a characteristic threshold that depends on the specific reaction pathway.
This behavior is rationalized by modelling the process through a size-dependent
polymerization rate. Our study highlights that the formation of
photopolymerized networks might be affected by the involved volumes regardless
of the specific curing mechanisms, which could play a crucial role in
optimizing photocuring-based additive manufacturing.
