Ellipsoidal shape manufacturing enabled by frontal polymerization with manually induced fluid field

Frontal polymerization (FP) has been reported as an energy-efficient and environment-friendly alternative to the traditional manufacturing of polymer composites. FP can only produce polymeric parts in rectangular or circular shapes without molds or a second manufacturing procedure. In the present work, using the reaction-diffusionconvection model, we demonstrate a concept of shape manufacturing for FP using manually induced fluid flow. The manually induced fluid field can lead to anisotropic front propagation, which produces a controllable ellipticity for the polymer products. Multiphysics finite element analyses reveal that the fluid field can introduce anisotropic front propagation, which produces a controllable elliptic shape of polymer products. A parametric study is conducted to establish the relationship between the processing conditions of frontal polymerization and the ellipticity of the FP-generated product, which is quantitatively described by a scaling law. According to the thermal analyses, a large fluid momentum can quench the front by carrying fresh resin at a lower temperature to the exothermic front. Detailed computations suggest that the final shape of the polymer produced by the quenched front can also be adjusted by leveraging the pre-gelling state of the resin, initial temperature, and the magnitude of the fluid field. A large fluid velocity will break the balance between reaction and diffusion, which causes the instability, leading to reaction patterns. This study provides a fundamental understanding of the interactions between the polymerization front and the manually induced fluid field. The results and findings lay the theoretical foundation for developing future FP-based manufacturing methods to achieve special shapes and patterning of polymeric parts by leveraging complex fluid dynamics.