In this Letter, we study the interaction between a self-sustaining exothermic reaction
front propagating in a direction perpendicular to that of gravity and the buoyancy-driven
convective flow during frontal polymerization (FP) of a low-viscosity monomer resin.
As the polymerization front transforms the liquid monomer into the solid polymer,
the large thermal gradients associated with the propagating front sustain a natural
convection of the fluid ahead of the front. The fluid convection in turn affects the
reaction-diffusion (RD) dynamics and the shape of the front. Detailed multiphysics
numerical analyses and particle image velocimetry experiments reveal this coupling
between natural convection and frontal polymerization. The frontal Rayleigh (Ra) number
affects the magnitude of the velocity field and the inclination of the front. A higher
Ra number drives instability during FP, leading to the observation of thermal-chemical
patterns with tunable wavelengths and magnitudes.
