Fluid convection driven by surface tension during free-surface frontal polymerization

Frontal polymerization (FP) is an efficient method to manufacture thermoset polymers and composites, and is usually modeled as a reaction–diffusion (RD) process. In this study, we investigate numerically and experimentally how fluid convection ahead of the propagating front can impact the reaction–diffusion balance in the free-surface FP of dicyclopentadiene (DCPD) and 5-ethylidene-2-norbornene (ENB). Multiphysics finite element analyses reveal how the velocity of the surface-tension-driven flow described by the dimensionless Marangoni number can be modulated by varying the processing temperature and the viscosity of the monomer resin. The surface-tension-driven fluid velocity exhibits two distinct regimes, which arise from the interplay and competition between thermal and chemical advection. The dispersion of the reaction heat by the Marangoni flow leads to a reduction in the velocity of the front. The presence of fluid convection during FP can lead to instabilities in the front propagation and generate reaction patterns, which can be adjusted by controlling the initial temperature and degree of cure. The numerical findings are corroborated by experiments that combine FP and particle image velocimetry (PIV).