Self-Assembly of Surfactants in Ionic Liquids: Mechanisms, Applications and Recent Developments

Surfactant self-assembly in ionic liquids (ILs) has attracted increasing attention because ILs provide highly tunable ionic environments that differ fundamentally from conventional aqueous media. Unlike water-driven aggregation dominated by the hydrophobic effect, self-assembly in ILs is governed by the cooperative interplay of solvophobic interactions, electrostatic screening, hydrogen-bond networks, specific ion effects, and solvent nanostructuring. Although substantial progress has been achieved during the past decade, a unified mechanistic understanding that links IL structure to aggregate morphology and functional performance remains lacking, and the literature is fragmented across system classes that are rarely compared under matched experimental conditions. This review presents a mechanism-oriented synthesis of surfactant self-assembly in IL media. The review is organized around an explicitly defined classification of IL-amphiphile systems, distinguishing neat IL media, IL-water mixtures, surface-active ionic liquids (SAILs), ILs used as cosurfactants, and conventional surfactants dissolved in ILs, and it states the literature-search strategy and eligibility criteria used to assemble the evidence base. The fundamental driving forces responsible for aggregation are then analyzed critically, with emphasis on how solvophobic interactions, electrostatic screening, hydrogen bonding, and packing-parameter modulation jointly determine aggregate formation and structural evolution, and on the quantitative thermodynamic and structural parameters, namely the Gibbs energy, enthalpy, and entropy of micellization, the critical micelle concentration (CMC), and the aggregation number, that make these contributions comparable between systems. Representative self-assembled architectures, including micelles, reverse micelles, lyotropic liquid crystals, microemulsions, and worm-like micelles, are discussed together with the resolution limits, artifacts, and applicable concentration ranges of the characterization techniques and simulation approaches used to resolve them. Applications in nanomaterial synthesis, electrochemical energy storage, drug delivery, enhanced oil recovery, and green separation technologies are reorganized around explicit structure-property-performance relationships, and claims that currently rest on schematic or correlative evidence are identified as such. Finally, a critical roadmap is presented that addresses reproducibility, standardized reporting, viscosity and transport limitations, impurity and water sensitivity, scale-up, cost, toxicity, recyclability, and quantitative predictive design, including realistic opportunities for machine-learning-assisted modeling. By integrating recent advances from molecular mechanisms to practical applications, this review provides a unified framework for understanding surfactant self-assembly in ionic liquids and offers guidance for the rational design of next-generation soft functional materials.