Hierarchical Epoxy Thermosets—Tuning Properties at Multiple Length Scales Through Phase Separation and Additive Manufacturing

The structure and properties of epoxy thermosets can be modified via polymerization-induced phase separation (PIPS). In this work, we utilized binary mixtures of components to induce phase separation, allowing for the control of both the phase size and composition in the phase separated material. The high tunability of the material’s morphology enables the generation of feature sizes ranging from the nano- to micro-scale as well as control of the composition – a hard matrix with soft domains, or a soft matrix with hard domains. The thermomechanical properties of these materials are very dependent on the morphology and composition of the material, and the highly tunable nature of the system allows for the selection of desirable properties for different application spaces. These phase separating epoxies have shown promise as shock resilient materials at high deformation rates, and there is further space to explore shock propagation behavior through the development of hierarchical materials with the control of properties at multiple length scales. Hierarchical epoxy thermoset materials can be created through the additive manufacturing of this PIPS epoxy framework, where mesoscale structures are controlled via phase separation and macroscale structures are controlled via additive manufacturing. To explore this material design space, direct ink write (DIW) printing was utilized. In order to use this manufacturing method, modification of the PIPS epoxy system was necessary to meet the rheological property requirements for printability. This presentation is focused on the development of printable phase separated epoxy materials using dual-cure formulations and thixotropic additives. Tradeoffs between printability and modifications to the phase separating material’s properties and structure at the meso- and macro-scale are investigated.