Metal-Ligand Coordination as a Strategy for Tuning the Viscoelasticity and Adhesion of 3D-Printable Ionic Liquid Polymer Networks

Abstract

Pressure-sensitive adhesives (PSAs) are soft viscoelastic materials that form adhesive bonds under light pressure and are widely used in applications ranging from medical devices to electronics. Their performance depends on balancing adhesion and cohesion, which requires materials to be soft enough to wet substrates during bonding while maintaining sufficient cohesive strength to resist deformation and failure during debonding. This balance is difficult to achieve because tack, peel strength, and shear resistance are governed by viscoelastic behavior across different deformation timescales. In addition, most PSAs are processed as films or tapes, limiting the ability to fabricate customized adhesive structures. This dissertation investigates 3D printable ionic liquid polymer networks with metal-ligand coordinated crosslinks as a platform for tunable pressure-sensitive adhesives. Ionic liquid polymer networks provide a soft, conductive, and adhesive material platform, while metal-ligand coordination introduces dynamic crosslinks that can alter frequency-dependent relaxation and energy dissipation. By combining permanent covalent crosslinks with reversible metal-ligand crosslinks, these materials can be designed to balance processability, cohesion, and adhesive performance. Chapter 1 introduces the adhesion-cohesion tradeoff in PSAs, the use of rheology and viscoelastic windows to relate frequency-dependent behavior to adhesive performance, and the role of ionic liquids and metal-ligand coordination in dynamic polymer networks. Chapter 2 describes the formulation and processing of metal-coordinate ionic liquid polymer networks for vat photopolymerization, showing how metal identity, ligand-to-metal ion ratio, and chemical crosslinker concentration affect printability and viscoelastic behavior. Chapter 3 examines the adhesive performance of these materials by correlating viscoelastic window analysis with loop tack and lap shear testing across formulations varying in metal identity, metal concentration, and chemical crosslinker concentration. Altogether, this work demonstrates that metal-ligand coordination can be used to tune the rheological and adhesive properties of 3D-printable ionic liquid polymer networks. These results provide a framework for designing multifunctional, additively manufactured PSAs in which dynamic and permanent crosslinks are used together to control relaxation behavior, cohesive strength, and adhesion across application-relevant timescales.