Systematic investigation of cationic monomeric, dimeric, and trimeric surfactants for self-assembly, adsorption thermodynamics, and enhanced oil displacement

Tailoring surfactant topology offers a powerful route to govern interfacial phenomena and fluid displacement in harsh subsurface environments. Herein, we systematically examine the influence of headgroup multiplication across three homologous tetradecyl quaternary ammonium architectures: single-chain MC14, dimeric GC14, and trimeric TC14. Spectroscopic characterization ( 1 H/ 13 C-NMR, FTIR) and thermogravimetric analysis (TGA) validated the target chemical frameworks and their thermal robustness, while XRD confirmed the predominantly calcitic, highly crystalline matrix of the evaluated carbonate substrate. Increasing the oligomeric degree substantially boosted surface activity and self-assembly propensity at 25 °C, lowering the critical micelle concentration (CMC) by two orders of magnitude from 3.50 mM (MC14) down to 0.114 mM (GC14) and 0.035 mM (TC14), alongside superior counterion association and surface packing efficiency. Dynamic light scattering (DLS) confirmed architecture-controlled supramolecular aggregation, tracking hydrodynamic sizes from 4.15 nm to 8.12 nm. Thermodynamic evaluations indicated spontaneous, increasingly exergonic micellization and elevated halotolerance against NaCl from monomeric to trimeric configurations. Under harsh thermal conditions (80 °C), TC14 outperformed lower-order homologues by reducing oil-water interfacial tension to a nadir of 0.21 mN/m and effectively reversing oil-wet carbonate wettability (contact angle shifted from 153° to 56° at 2 ×CMC). Synergistic tuning with sulfate ions further decoupled conditions required for minimal interfacial tension from those favoring maximal hydrophilicity. Crucially, capillary-dominated spontaneous imbibition experiments revealed that wettability-tailored TC14 solutions yielded a peak recovery of 22.1%, outperforming baseline seawater (12.7%). These insights elucidate the mechanistic advantages of multivalent trimeric surfactants as ultra-low-dosage, salt-tolerant agents for interfacial engineering and enhanced hydrocarbon recovery in carbonate formations.