Poly(Ionic Liquid)s Dispersants for Lubricants: A Review on Structure–Property Relationships

Poly-(ionic liquid)-s (PILs) have emerged as a versatile class of materials whose structural diversity, ranging from backbone chemistry and side-chain functionality to counterion type, governs their aggregation behavior, interfacial adsorption, and nanoscale self-assembly. These attributes make PILs attractive candidates for advanced applications in lubrication, dispersion stabilization, and sustainable functional materials. However, correlating molecular architecture with macroscopic performance remains a significant challenge, largely due to the complex and dynamic nature of their structural evolution. This review critically examines recent progress in understanding PIL structure-property relationships through multiscale characterization. Surface tension provides insight into interfacial activity, while small-angle X-ray scattering and small-angle neutron scattering elucidate nanoscale organization and hierarchical assembly. Complementarily, zeta-potential measurements quantify electrostatic interactions and the colloidal stability. Together, these techniques enable a coherent framework linking molecular design, interfacial phenomena, and bulk performance. Key knowledge gaps are highlighted, including the need for in situ and operando studies under realistic operating conditions as well as the integration of experimental techniques with computational modeling to capture dynamic restructuring and long-term stability. By synthesizing insights across structural chemistry, scattering techniques, and interfacial science, this review establishes future research directions for the rational design of PILs as next-generation dispersants, lubricants, and sustainable advanced materials.