A finite deformation theory of desolvation and swelling in partially photo-cross-linked polymer networks for 3D/4D printing applications.

Photopolymerization is a process strongly dependent on the light field in the resin. This typically results in a non-uniformly crosslinked network where some parts of the network are fully cross-linked while other parts are partially crosslinked. The partially crosslinked part could exhibit a high volume expansion upon swelling and a high volume shrinkage upon desolvation. Through control over the light field in the photopolymer resin, this feature has been used to create solvent responsive shape changing structures as well as 3D/4D printed smart devices, showing promising application potential. In this paper, we develop a finite deformation theory to consider the nonuniform crosslink density of the network and the interaction between different species inside the network. The mechanical properties of the network are correlated with the reaction process and the existence of residual uncrosslinked monomers is included in the partially crosslinked network. The efficiency of the theory is proved by the finite element simulations of two special applications of the partially crosslinked network.