MD Simulations Of The Effect Of Inorganic Salts On Aggreation Behavoir Of Anionic Surfactants At The Oil/Water Interface

Anionic surfactants play an important role in tertiary oil recovery,and one of their principles is reducing the interface tension of oil/water interface through oriented adsorption at the interface.Since anionic surfactants in aqueous solution can decompose into counterion and the negatively charged active part,mineral salts including Na⁺?Mg²⁺ and Ca²⁺ can significantly affect surface activity of anionic surfactants.The investigation on the influence of salt ions in anionic surfactants adsorption at the oil/water interface would be useful to understand the relative experimental phenomena and the salt-tolerant mechanism of anionic surfactants.In view of this,the dynamics process of anionic surfactants moving from water solution to the oil/water interface is preliminarily explored by using molecular dynamics?MD?simulations in this paper.On that basis,the effect of salt ions on the dynamics process of anionic surfactants moving to the oil/water interface is investigated.And then,molecular dynamics simulation is used to study the influence of salt ions in the interfacial propertites of anionic surfactant adsorpted at iol/water interface.As the dynamics process of surfactants moving from water solution to the oil/water interface is preliminarily explored in this paper,the rationality of the initial model is vertified.Simulation results show that the order of the interfacial activity of Sodium dodecyl sulfate?SDS?,Sodium dodecylbenzene sulfonate?SDBS?,Sodium lauryl polyoxyethylene ether sulfate?AES?and Sodium dodecyl polyoxyethylene ether carboxylate?AEC?is: AES>AEC>SDBS>SDS,which is in coinsident with the reported experimental results.And this result indicates that the initial model is reasonable.The dynamics process of anionic surfactants adsorption shows that the influence of Mg²⁺ concentration in SDBS surfactant is larger that than of Na⁺ concentration;Compared with the effect degree of Mg²⁺,the effect degree of Ca²⁺ on the interfacial activity of AES is more severe;The salt-tolerance of AES is supercior to that of SDBS.The properties of anionic surfactants adsorpted at the oil/water interface shows that inorganic salts have influence in AES molecules configuration,the electricial double layer,the hydration of AES heads and the binding tendency between ions and AES heads;The impact degrees of inorganic salts on properties above of AES systems follew the order: Ca²⁺>Mg²⁺>Na⁺,which is in coincident with the reported experimental results about the effect of salt ions on the interfacial activity of AES adsorpted at the oil/water interface;Besides,in the condition of high concentration of Ca²⁺ in AES system,Ca²⁺ can bind with AES heads forming calcium compound which has low solubility,resulting in reducing AES hydrophily and AES molecules prefer to lay in the oil/water interface.