Impact of size effects on photopolymerization and its optical monitoring in-situ

TL;DR

This study investigates how layer thickness influences photopolymerization in 3D printing, revealing size-dependent effects on curing time and network formation through in-situ optical monitoring and modeling.

Contribution

It introduces a size-dependent model for photopolymerization rates and demonstrates the impact of volume on curing efficiency in additive manufacturing.

Findings

Curing time increases as volume decreases below a threshold.

Size effects influence network formation regardless of curing mechanism.

Optical monitoring enables real-time analysis of polymerization dynamics.

Abstract

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.