Enhanced Solubility of Dicofol through Micellization in Anionic and Cationic Surfactant Systems at Different Temperatures: A Conductometric Study and Thermodynamic Analysis

Abstract

This study investigates the interactions of the insecticide dicofol with simple micellar systems. Conductometric measurements were employed to examine the interactions between dicofol and aqueous anionic (SDS) and cationic (TMTFB) surfactants under varying temperature conditions (303.15–331.15 K). The concentration of dicofol ranged from 0 to 25 µmol·L⁻¹. The observed decrease in the critical micelle concentration (CMC) in the presence of dicofol indicates a strong association between the surfactant molecules and the insecticide. A 21% reduction in the CMC of SDS was observed, compared with a 57.61% decrease for TMTFB at 303.15 K, indicating a stronger interaction between dicofol and the cationic surfactant. The critical micelle concentration (CMC) of the surfactants, as well as the thermodynamic parameters of micellization (ΔH°, ΔS°, and ΔG°), were determined. The negative values of the standard free energy of micellization (ΔG°) ranged from −37.8 to −36.56 kJ·mol⁻¹ for SDS and from −38.26 to −34.29 kJ·mol⁻¹ for TMTFB. Furthermore, the variation of specific conductivity as a function of surfactant concentration at different temperatures (303.15–331.15 K), in the presence of 1 µmol L⁻¹ dicofol, revealed that the CMC of TMTFB changes significantly (≈33%), whereas that of SDS remains essentially constant. Under these conditions, the standard free energy of micellization (ΔG°) ranged from −46.52 to −39.74 kJ·mol⁻¹ for SDS and from −51.42 to −40.50 kJ·mol⁻¹ for TMTFB. The results demonstrate a decrease in CMC with increasing dicofol concentration and temperature, confirming both the effective solubilization of dicofol in the two micellar media and the thermodynamically favorable nature of the micellization process. The positive standard enthalpy values (ΔH° > 0) indicate that the interactions between dicofol and the surfactants are endothermic, while the positive standard entropy values (ΔS°) suggest that the micellization process is predominantly driven by entropic contributions.