Architecting interfacial resilience: A gemini ionic liquid for steel protection under extreme acid attack

Conventional wisdom in inhibitor design often marginalizes the intramolecular distribution of active sites, which becomes decisive under extreme conditions. Here, we report a thermally stable Gemini ionic liquid (GIL), C6(2-MI12)2Br, specifically tailored to safeguard N80 steel in aggressive downhole acidizing environments. Characterized by a dual-imidazole architecture and twin dodecyl chains, the GIL exhibits thermal resilience up to 232 °C. Weightlessness and electrochemical assessments identify the molecule as a robust mixed-type inhibitor, delivering an inhibition efficiency of 91.68% in 15% HCl at 363 K, which elevates to 99.34% through a “skeleton-filling” synergy with propynol ethoxylate. In situ Scanning Vibrating Electrode Technique (SVET) resolves an interfacial potential homogenization pathway, wherein the inhibitor suppresses localized corrosion hotspots. Thermodynamic and kinetic analyses resolve a medium-dependent mechanistic divergence: inhibition is entropy-controlled via chemical anchoring in dilute acid (1 M HCl), shifting to an enthalpy-driven physical barrier mechanism in concentrated acid (15% HCl). Density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulations link these trends to oriented orbital overlap (Eads = -10.71 eV) and self-assembly of a dense, thermally resistant film. Mechanistically, exceptional protection arises from a multi-mode transition: adsorption initiates through rapid electrostatic anchoring of quaternary ammonium centers, evolving into a stable physiochemically dominated regime involving N-Fe coordination and hydrophobic repulsion. This dynamic assembly constructs a robust molecular shield that intercepts corrosive species and facilitates the immobilization of corrosion products (Fe2O3, FeOOH). These results establish a comprehensive multi-scale framework for programming high-performance interfacial protection in extreme industrial environments.