Molecular Dynamics Simulation Of The Aggregation Behavior Of Anionic/Zwitterionic Surfactant Mixed System At Oil/Water Interface

The development of high effiency and low cost has been a hot topic in the field of chemical industry,molecular dynamics method can be used to clarify the self-assembly behavior of surfactants at the molecular level,but it is difficult to achieve the consitions by the traditional experiment.Molecular dynamics simulation method was used to study the aggregation behavior of the surfactant mixed system of N-Dodecyl-N,N-Dimethyl-3-Ammonio-1-Propanesulfonate?SB12-3?/Sodium Dodecyl Benzene Sulfonate?SDBS?at oil/water interface and the interaction between SB12-3 and SDBS.And the salt tolerance and alkali resistance of the mixed system were also investigated.1.Interface formation energy?IFE?was used to screen the best ratio of the SB12-3/SDBS mixed system.The simulation results showed that there were well synergistic effects between SDBS and SB12-3,and the synergistic effects reached maximum when the ratio of SDBS and SB12-3 was 4:6 due to the lowest value of IFE.There was strong interaction between –SO3-of SB12-3 and hydrogen atoms of water molecules.-N+ in SB12-3 preferentially approached to-SO3-in SDBS by the electronic interaction,making two surfactants intertwined with each other.This is a phenomenon indicated that –SO3-in SDBS was protected that it was under minor influence in the mixed system,so-SO3-in SB12-3 was the main hydrophilic group of SB12-3/SDBS surfactant mixed system.2.Radial distribution function and order parameter were used to study the salt resistance of SB12-3/SDBS surfactant mixed system.Ca²⁺ and Mg²⁺compressed the headgroups of SB12-3 and SDBS and made them arrange more closely at the oil/water interface,this changed the aggregation behavior of SB12-3/SDBS surfactant mixed system and make the amphiphilic properties of the mixed system better.In addition,the impact of Mg²⁺on the mixed system is stronger than Ca²⁺.However,the concentration of Na+ have almost no influence of the aggregation behavior of SB12-3/SDBS surfactant mixed system.3.The interfacial activity of SB12-3/SDBS surfactant mixed system was improved when Na OH was at the concentration of 0.6%-1.2%,but when the mass concentration of Na OH reached 1.2%,the interfacial activity decreased obviously.This is due to the OH-in Na OH will become priority to water to form the hydrogen bonds,made the number of hydrogen bonds between headgroups of surfactant and water decreased sharply so that the hydrophilic of SB12-3/SDBS surfactant mixed system decreased.We also studied weak base Na2CO3,and the simulation results showed that the interfacial activity of SB12-3/SDBS mixed system became increasingly with the mass concentration of Na2CO3 increased.