Effect Of Molecular Structure On Foam Stability Of Gemini Surfactants By Molecular Dynamics Simulation

As a new type of tertiary oil recovery method,foam flooding have the high apparent viscosity and selective plugging,can improve the recovery efficiency from sweep efficiency and displacement efficiency.Foam flooding is the complement of conventional three mining technology.Foam stability is one of the most important factors which can limit the foam flooding's widely application,so how to improve foam stability became the first issue to foam flooding.At present,the traditional surfactants have been difficult to meet the needs of the production of oil or gas,but the present of Gemini surfactant offers a new way for the development of efficient foaming agent.Using molecular dynamics?MD?method,we studies effect of molecular sturctur on anionic Gemini surfactant include the type of polar head,the length of hydrophobic tail,and the linkers on foam stability,to clear the connection between the molecular structure and foam properties,and to explore the mechanism of gemini foam.The results of polar headgroups show that the type of headgroup has a great influence on foam stability.From the carboxylate?12-3L-12?,sulfonate?12-3Sn-12?to sulfate?12-3S-12?system,the order of headgroup is reduced,and the interaction between headgroups and water molecules is increased,in turn the ability of headgroup binding water molecules is gradually reduced,so the foam stability is reduced in order.The results of hydrophobic tail show that the length of chain length less affected the polar head group and water molecules.The hydrophobic tails increase the foam stability is owning to the hydrophobic interactions.With the length increase,the interaction between hydrophobic tail is enhanced,the mechanical strength of interface adsorption layer is also increased.Closely adsorption layer can effectively reduce gas permeation,and improve foam stability of foam film.So with the carbon number increase,the foam stability of gemini surfactant system is increased.The results of spacer show that the length of spacer can affect both the nature of head and tail chain of gemini surfactants.From three CH₂ to six CH₂,the foam stability is increased.This is mainly attributed to supporting function of spacer,the longer spacer can screen the interaction between the headgroups,to reduce the repulsion between polar headgroups,to increase polarity attraction between head and water,so as to increase the foam stability.But when the number of spacer still increased,for example,from six CH₂ to nine CH₂,the foam stability of gemini surfactant system is reduced.although long spacer can reduce the repulsion between polar headgroups,but overlong spacer make the monolayer structure porous,which is adverse to the stability of foam liquid.