Molecular Insight Into The Oil/Water Interfacial Property Of Amphiphilic SiO₂ Nanoparticles

Recently,the development of low-permeability reservoirs has attracted great attention because of the dramatically growing energy consumption.However,it is still challenging to develop low-permeability reservoir because that traditional tertiary oil recovery techniques cannot work well due to the complexity of reservoir situation.Developing oil recovery techniques is urgently required,for example,the use of nano-materials.Silica nanoparticle is easy to be modified,which could facilitate the design and development of efficient oil-displacement agents for low-permeability reservoirs.Besides,the low-cost silica nanoparticle is financially advantageous for the large consumption in oil displacement.The recovery efficiency depends on the sweep efficiency and the displacement efficiency of oil recovery agent.Silica nanoparticles can greatly improve the sweep efficiency by increasing the viscosity of oil recovery agent.However,pure silica nanoparticle is inadequate in the displacement efficiency,which needs to be improved.Fortunately,modifying silica nanoparticles with alkyl chains may be a promising solution for this problem.In this work,with molecular dynamics simulation,we gave molecular insight into the oil/water interfacial activity of silica nanoparticles modified with alkyl chains.With studying the effect of modification,we aimed to reveal the mechanism of modified silica nanoparticles in decreasing the oil/water interfacial tension.To decrease oil/water interfacial tension,silica nanoparticles should stay at the interface.However,we found that pure silica nanoparticles could not migrate from water to oil/water interface,which is the reason for the insufficiency in interfacial activity.With modification,we found that silica nanoparticles can easily migrate to the interface owe to the drag of alkyl chains.Moreover,the modified silica nanoparticles can increase the thickness of the oil/water interface,which also benefit the decrease of interfacial tension.We also studied the effect of the ratio of modified hydrophilic/hydrophobic groups on the interfacial activity.The dodecane and hydroxyl were adopted in modification.We found that the interfacial activity reaches the highest point when the difference between nanoparticle/oil interaction energy and nanoparticle/water interaction energy is minimum.However,only when the particle/oil interaction energy does not reach a single peak can we get this result.With setting the ratio of modified hydrophilic/hydrophobic groups as 1:1,and altering the type of the modified groups,we also obtained the result that “the interfacial activity reaches the highest point when the difference between nanoparticle/oil interaction energy and nanoparticle/water interaction energy is minimum”.Furthermore,the effect of nanoparticles on the thickness of oil/water interface could be higher with bigger particle/oil interaction energy,which generates stronger ability in decreasing the oil/water interfacial tension.