Methylene Blue and DTAB Synergy for Wettability Modification in Saline Media

Methylene blue (MB) can modify the wettability of carbonate and sandstone surfaces; however, its performance deteriorates with increasing salinity as chloride ions neutralize its positive charge, weakening electrostatic attraction, and reducing adsorption stability. To overcome this limitation, dodecyltrimethylammonium bromide (DTAB) was introduced as a co-surfactant to preserve MB’s cationic charge through electrostatic shielding, thereby stabilizing its interfacial behavior under saline conditions. Comprehensive analyses of surface and interfacial tension, zeta potential, thermal stability, and contact angle were conducted across salinities from 0 to 854 mM TDS and temperatures from 25 to 80 °C. Results show that DTAB reduces the critical micelle concentration and interfacial tension while maintaining MB’s positive charge and enhancing its adsorption on both carbonate and sandstone surfaces. The average of the lowest contact angle with MB alone was 92.7° on carbonate and 109.7° on sandstone, indicating weak wettability modification. When combined with DTAB, the angles decreased markedly to 30.5° and 56.7°, respectively, confirming strong and stable wettability alteration across salinity and temperature ranges. These findings demonstrate that DTAB effectively stabilizes MB’s electrostatic functionality, ensuring consistent interfacial performance and providing new insight into the design of surfactant-dye-dye systems for controlled wettability in saline environments.