Interfacial tension reduction mechanism by alkaline-surfactant-polymer at oil-water interface from experimental and molecular dynamics approaches

Enhanced demulsification of alkaline-surfactant-polymer flooding O/W emulsion by multibranched polyether-polyquaternium based on the size effect of oil droplets

In the alkaline-surfactant-polymer flooding emulsion, oil droplets with various sizes exhibited different interfacial properties, resulting in different stabilization and destabilization behaviors. In view of this, it is expected to achieve outstanding oil-water separation efficiency by screening targeted demulsifier for oil droplets with different size ranges (0-1, 1-5 and 5-10 μm). Based on the size effect of oil droplets, a series of multibranched polyether-polyquaternium demulsifiers that integrated different charge neutralization and interfacial displacement functionalities were designed by regulating the cationicity and EO:PO ratios. As a result, the most effective polyether-polyquaternium variant for each size range of oil droplet was screened out. By employing these three selected polyether-polyquaternium variants in a sequential batch demulsification test, the maximum demulsification efficiency of 95.1% was obtained, which was much higher than that using a single polyether-polyquaternium variant (82.5%, 80.5% and 83.8%). The adsorption behaviors of polyether-polyquaternium variants on the oil/water interface were investigated by the molecular dynamics simulation. Moreover, the interfacial properties and oil droplet size variations during the demulsification process were monitored, so as explore the demulsification mechanism. This demulsification protocol based on the size effect of oil droplets with its excellent oil-water separation performance offered significant technical promise for the emulsified oil wastewater disposal.

Insights into Zwitterionic Surfactant Interactions at the Oil-Water Interface by Interferometry Experiments and MDS Calculations

In this work, the interaction performance of zwitterionic surfactant [dodecyl dimethyl sulfopropyl betaine (DSB-12) and hexadecyl dimethyl sulfopropyl betaine (DSB-16)] at the n-octadecane oil surface is investigated from experimental and simulation insights. For a macroscopic experiment, interfacial interferometry technology was developed for real-time monitor interaction performances and to obtain the quantitative interfacial thickness and mass results. The Langmuir model was characterized by thermodynamic analysis, deducing the aggregation spontaneity of DSB-16 > DSB-12 with ΔGagg(DSB-16) = -5.94 kJ mol-1 < ΔGagg(DSB-12) = 24.08 kJ mol-1. A three-step dynamic model (adsorption, arrangement, and aggregation) was characterized by kinetic analysis, indicating arrangement process as slow-limiting step with k2(arr) < k1(ads), k3(agg). For microscopic simulation, and molecular dynamic (MD) method was utilized to theoretically investigate interaction performances and obtain the interfacial configuration and energy results. The interaction stability and interaction strength were indicated to be DSB-16 > DSB-12 with differences of final energy ΔEfin = 48-88 kcal mol-1. The interaction mechanism was explained by proposing the model of "response enhancement" and "deposition activity" for DSB-16 interactions, and "response decrease" and "elution activity" for DSB-12 interactions. The different performances can be attributed to the different interaction forms and forces of surfactants. This work provided a platform for performance and mechanism investigation between the surfactant molecule and oil surface, which is of great significance in reservoir exploitation and enhanced oil recovery (EOR).

Synergistic Interaction of Hyperbranched Polyglycerols and Cetyltrimethylammonium Bromide for Oil/Water Interfacial Tension Reduction: A Molecular Dynamics Study

Applying surfactants to reduce the interfacial tension (IFT) on water/oil interfaces is a proven technique. The search for new surfactants and delivery strategies is an ongoing research area with applications in many fields such as drug delivery through nanoemulsions and enhanced oil recovery. Experimentally, the combination of hyperbranched polyglycerol (HPG) with cetyltrimethylammonium bromide (CTAB) substantially reduced the observed IFT of oil/water interface, 0.9 mN/m, while HPG alone was 5.80 mN/m and CTAB alone IFT was 8.08 mN/m. Previous simulations in an aqueous solution showed that HPG is a surfactant carrier. Complementarily, in this work, we performed classical molecular dynamics simulations on combinations of CTAB and HPG with one aliphatic chain to investigate further the interaction of this pair in oil interfaces and propose the mechanism of IFT decrease. Basically, from our results, one can observe that the IFT reduction comes from a combination of effects that have not been observed for other dual systems: (i) Due to the CTAB-HPG strong interaction, a weakening of their specific and isolated interactions with the water and oil phases occurs. (ii) Aggregates enlarge the interfacial area, turning it into a less ordered interface. (iii) The spread of individual molecules charge profiles leads to the much lower interfacial tension observed with the CTAB+HPG systems.