Molecular Control via Dynamic Chemical Bonding Enables Material-level Responsiveness in Additively Manufactured Metallo Polyelectrolytes (MPEC)

One class of materials, metallo-polyelectrolyte complexes (MPEC), is unique in that it contains organic frameworks that can undergo reversible electrostatic interactions through the formation and dissociation of dynamic bonds. They consists of negatively charged polyanions crosslinked by metal cations via electrostatic interactions. These molecular-level processes give rise to a wide range of material dynamic responses, for example, stimuli-responsiveness, self-healing, dissolution in solvent, and improved toughness through enhanced energy dissipation. The knowledge gap between molecular-level chemistry of dynamic bonds and continuum-level material properties have limited the development and utilization of these materials in real-world applications. Existing state-of-the-art fabrication methods typically involve cumbersome, multi-step solution-based synthesis, and the multitude of time/length scales in actuation and stimulus-driven response of MPECs presents computational challenges, which limits theoretical guidance for experiments.<br/><br/>We demonstrate a single-step stereolithography-based additive manufacturing (AM) method to produce MPEC gels, which produces homogeneous, stable, and long-lasting materials using a straightforward synthesis route. We demonstrate that the AM-fabricated MPEC gels<br/>allow for tunability in their mechanical response via two control parameters: (1) metal ion valency and (2) polymer charge sparsity. We discover that the mono-, di-, and trivalent metal ions afford control of the coordination environment and bond strength within the polymer matrix, which propagates to the macroscale properties where higher valency ions result in stiffer and tougher materials. This work provides a comprehensive understanding of the metallo-polyelectrolyte behavior and lays out their parameter space, enabling selective design of advanced compliant and multifunctional materials.