| As a non-renewable fossil energy source,the crude oil known as "industrial blood"is still the main energy source used today.In recent decades,with the deepening of human industrialization and increasing of the world's population,consumption of crude oil has increased,causing that proven oil reserves will be exhausted in the expected decades.Now new energy have yet been discovered,but coal and natural gas conversion technologies are far from mature,so that the energy humans depend on is becoming increasingly tense.After primary oil recovery and secondary oil recovery have been unable to meet the huge energy needs of human beings,tertiary oil recovery has played a very important role in improving oil recovery.Compared with other surfactants for oil displacement,alkyl-benzene sulfonate is widely used in the oilfield industry.However,industrial alkyl-benzene sulfonates are usually a mixture of various isomers,which have different alkyl carbon numbers,different alkyl chain numbers,and different positions of sulfonic acid groups attaching to the benzene ring.It is difficult to study the structure and properties of individual components of such surfactants because that the effect may be due to the synergistic behavior of certain components.Therefore,it is particularly important to continue to improve oil recovery by synthesizing different types of alkyl-benzene sulfonates with higher purity and studying the relationship between their structure and oil-water interface properties and aggregation behavior.This paper design and synthesize sodium dodecyl benzene sulfonate isomeric with high purity,then study the influence of molecular structure,concentration,temperature and inorganic salt on oil-water interface properties by experimental means.The molecular dynamics simulation reveals the kinetic and structural information of the surfactant molecules on the oil-water interface at molecular level.In addition,we mix the anionic surfactant with the cationic building element molecules to construct a pseudogemini surfactant system and explore the effect of structure on the ordered molecular aggregation behavior.This paper consists of the following five parts:Section ?:Mainly introduces the application of surfactants in enhanced oil recovery,the classification and development of surfactants for oil displacement,the synthesis and research progress of alkylbenzene sulfonates,experimental study on the properties of different kinds of alkylbenzene sulfonates at oil-water interface and theoretical studies using molecular dynamics simulations,investigation of the aggregation behavior of alkylbenzene sulfonates in pseudogemini surfactant systemsSection ?:Three sodium dodecylbenzene sulfonate isomerics were designed,and a series of high purity samples were synthesized in the laboratory through a series of steps such as alkylation,sulfonation,neutralization and separation and purification.The samples were characterized by HNMR and IR spectrometer.The dynamic interfacial tension of these three sodium dodecylbenzene sulfonate isomerics was systematically studied.The effects of concentration,inorganic salt and temperature were discussed.Studies have shown that at the same concentration,the branch(5,6)has the best effect of reducing the interfacial tension of oil-water,but the equilibrium time required is the longest;the addition of inorganic salts NaCl,CaCl2 and MgCl2 will cause the increase of oil-water interface cations.The repulsion between the head groups is weakened,resulting in a decrease in the oil-water interfacial tension during equilibrium,wherein CaCl2 has the best effect;in addition,as the concentration of inorganic salts increases,the interfacial tension decreases and then tends to moderate,wherein the branches(5,6)The change of oil-water interfacial tension is the smallest,indicating that its salt resistance is the best;at the same concentration,with the increase of temperature(from 20? to 60?),the oil-water interfacial tension of the three samples is increasing.It is indicated that the increase of temperature destroys the adsorption and arrangement of surfactant molecules at the oil-water interface,thus reducing the activity of the active agent molecules.The addition of inorganic salts has little effect on the surface tension of sodium dodecylbenzene sulfonate,but it significantly reduces CMCSection III:The modulus and phase angle of three sodium dodecylbenzene sulfonates were measured by TRACKER interfacial tension/rheometer.The influence of concentration,frequency,inorganic salt and temperature on interface dilatational modulus and phase angle were studied.The results show that the dilatational modulus of the three sodium alkylbenzene sulfonates reaches a maximum with increasing concentration;the oil-water interface dilatational modulus of the three alkylbenzene sulfonates increases with the increase of the frequency,because the interface deformation speed gradually increases as the frequency increases gradually,the surface The surfactant molecules can't repair the interfacial tension gradient to increase the interfacial expansion modulus.With the increase of CaCl2 concentration in the system,the dilatational modulus of the three sodium dodecyl benzene sulfonate solutions increases rapidly.It indicates that the addition of CaCl2 enhances the interaction of surfactant molecules at oil-water interface.When the CaCl2 concentration increases to a certain extent,the addition of CaCl2 no longer acts on the molecular interaction,and the oil-water interface is adsorption saturation,MgCl2 is similar to CaCl2;the dilatational modulus of three surfactants decreases with increasing temperature(from 20? to 60?);at lower concentrations,the diffusion exchange process in sodium alkylbenzene sulfonate solution contributes small,the phase angle is low,and the interface film is mainly elastic.As the concentration increases,the phase angle increases gradually,and the interface film viscosity increases.The addition of inorganic salt first increases the viscosity of the interface film,and then gradually increases the elasticity of interface film.;the addition of inorganic salt MgCl2 will first increase the viscosity of the interface film,and then gradually increase the elasticity of the interface film;the increase of temperature exacerbates the thermal motion of the molecule and enhances the diffusion of the surfactant between the bulk phase and the interface.Therefore,the adhesive portion of the interface film at a certain frequency is lowered,and the phase angle is decreased.Section IV:The molecular dynamics method was used to construct the theoretical model of oil-water interface.The aggregation behavior of alkylbenzenesulfonate(sodium salt)molecules at the oil-water interface was studied by using professional software such as Gromacs and Materials Studio.The density profiles of the different components and groups of the surfactant molecules show that the hydrophilic group(-SO3-)and the hydrophobic alkane chain are not completely in the same plane,interface adsorption single layer film of branched structure(i,j=3,8),(i,j = 5,6)is more stable than linear(i,j = 0,11).The radial distribution function between the rigid groups of the surfactant molecules was calculated.It was found that there was a strong and complex interaction between the benzenesulfonic acid groups,and the distribution function about the diameters of the water molecules and sodium ions around the polar groups were counted,it is found that the first hydration layer has both water molecules and sodium ions.The water molecules directly interact with the oxygen atoms in the polar groups through hydrogen bonds,with the greatest binding effect and the most stable structure.The water molecules in the layer interact with the water molecules in the first hydration layer mainly in the form of hydrogen bond donors to form a hydrogen bond network structure;from the spatial distribution function diagram,it can be seen that when the salt bridge is formed,sodium ions tend to form a 1:1 type,that is,a sodium ion directly coordinates with an oxygen atom in the polar group;the arrangement of the surfactant at the oil-water interface is calculated and counted,and the results show that the benzenesulfonate group The closer the group is to the middle of the alkane chain,the smaller the angle between the surfactant molecule and the normal of the oil-water interface and the more concentrated the distribution.The surfactant(5,6)has a stronger orientation and surface activity;effect of increasing temperature on hydrogen number is little,but the hydrogen bond lifetime formed between the three surfactant molecules and the water molecules decreased with increasing temperature,and among all three temperature gradients,the hydrogen bond formed between(5,6)and the water molecule has the longest life,indicating that(5,6)has the strongest temperature resistance.Section V:A cationic double-headed linker[mim-C4-mim]Br2 were designed and synthesized,which is mixed with SDBS of linear(0,11)and branched(3,8)at a molar ratio of 1:2.We systematically investigated the effects of different kinds of SDBS on the aggregation behavior of pseudogemini surfactant systems.Studies show that,from the phase behavior of the two systems,we can see:(1)the same point:with the increase of concentration,both systems have observed rich phase behavior,aqueous two-phases and the phase transformation from micelles to vesicle phase.(2)Differences:As the concentration increases,the phase transformation speed of two systems from the micellar phase to vesicle phase is inconsistent.At the same concentration,the phase behaviors of the two systems are different.The concentration of aqueous two-phases disappearance is different,[mim-C4-mim]Br2-(SDBS)2-(3,8)have a lower aqueous two-phases appearance concentration than[mim-C4-mim]Br2-(SDBS)2-(0,11),appearance concentration of the vesicle phase is also lower,the vesicle phase of[mim-C4-mim]Br2-(SDBS)2-(3,8)appears at about 75 mM,while[mim-C4-mim]Br2-(SDBS)2-(0,11)is at about 100 mM.In addition,it can be found from the Cyro-TEM image that the[mim-C4-mim]Br2-(SDBS)2-(0,11)system forms polydisperse vesicles at a higher concentration,In the system of[mim-C4-mim]Br2-(SDBS)2-(3,8),onion-like spherical multi-layered vesicles were observed. |
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