Microstructure control in printable porous polymer composites

Abstract

The microstructure of a porous polymer matrix composite, specifically the organization of polymer, particles, and pores, plays a defining role in the physical properties of the material. Developing materials and processes that allow us to control the microstructure gives us a powerful tool to create materials with designed performance. Here, a series of porous polyvinylidene fluoride (PVDF) and alumina (Al2O3) composites produced through evaporation induced phase separation (EIPS) are demonstrated. This process utilizes solution processable inks and achieves porosity via a simple drying procedure. This enabled the materials to be printed using direct ink writing (DIW) techniques. The effects of particle size and loading on the mechanical properties and microstructures of these materials were studied. It was found that these materials remain significantly more ductile and extensible than what is expected from particle reinforcement. In the most extreme case, the use of 300 nm Al2O3 particles were found to only minimally reduce strain at failure, even at high loadings. We believe this behavior is enabled by how the EIPS process alters the microstructure of the material and appears to preferentially locate particles at the polymer-pore interface.