Interaction Between Surfactin And Anionic/Cationic Surfactants

Surfactin is a kind of biosurfactant with cyclic peptide which produced by microorganism.It gets high attention due to its excellent interfacial activity and specific biological activity.Heavy alkyl benzene sulfonates(HABS),a series of typical petroleum-based anionic surfactants,have a wide range of industrial applications such as tertiary oil recovery.Mixtures of surfactants always show synergistic effect due to the interaction between different surfactants.In this work,we focus on the biosurfactant,surfactin,and several synthetic surfactants,and the intermolecular interaction between biosurfactant and synthetic surfactants both at interface and in mixed micelles have been studied,and the content contains four parts as follows:1)The component of HABS from Daqing oil Refinery was analysed using HPLC-MS,and the results showed that it is a mixture of twelve alkyl benzene sulfonates that with a carbon number in hydrophobic chain of 12-25 except 14,15.Those alkyl benzene sulfonates,the carbon number in hydrophobic chain of which is 12,13,16,17,and 18,are the main component of the HABS,and they have a mass content of 86.5%of the total alkyl benzene sulfonates(ABS).ABS with alkyl chain C12,C13,C16,C17,C18,and C19,were separated by preparative HPLC and their interfacial activities were studied.The results show that the bigger the hydrophobic chain of the ABS,the lower the critical micelle concentration(cmc)values.C16ABS exhibits the the most prominent activity in reducing the crude oil/water interfacial tension,and it can lower the interfaical tension of the crude oil/simulated formation water to an ultra-low IFT value.There may occur synergism between surfactant and ionized organic acids in the crude oil produced by alkali.2)The dynamic interfacial tensions(IFT)between crude oil and aqueous solutions of lipopeptide/HABS/Na2CO3 mixtures have been studied.The results show that,at a certain concentration of mixture surfactant and Na2CO3,the IFT could be reduced to ultra-low(<10-2 mN/m)when the lipopeptide content in the surfactant mixture was within a range of 10-50%(m:m),even to a level of 10-4 mN/m for the equilibrium IFT.In a fixed Na2CO3 concentration,the higher lipopeptide content in the surfactant mixture,the lower surfactant mixture concentration was required to make equal reduction in IFT.The amount of HABS could be reduced by over than 99%when the content of lipopeptide was increased from 10%to 50%.There existed strong synergism between lipopeptide,HABS,and ionized acids which was in-situ produced.There were two functions of Na2CO3,one is that Na2CO3 may react with acids present in crude oil and in-situ produce ionized organic acids which would participate in reducing IFT;the other is that the repulsion between the head groups in two anionic surfactants(lipopeptide and HABS)could be screened by Na+ and thus the the interfacial activity was strengthened.3)Interaction between surfactin and three alkyl benzene sulfonates,C16ABS,C17ABS,and C18ABS was studied by surface tension,fluorescence measurement,and dynamic light scattering(DLS)methods.Various parameters including interaction parameters(?? and ?m)and thermodynamic properties have been determined.Negative values of ?? and ?m indicated that there are attractive intermolecular interaction though these two surfactants are all negatively charged.Such an unexpected attractive interaction might be attributed to the arrangement of alkyl benzene sulfonates and surfactin molecules into a spatial configuration that either reduces the electrostatic repulsion or promotes the hydrophobic interaction between alkyl chains.The formations of mixed monolayer at air-water interface and mixed micelle in solution are both thermodynamically feasible processes.The results of fluorescence and DLS measurements indicate that more compact and lager aggregates are formed in mixed surfactants,and large aggregates in rod-shaped and lamellar micelle or vesicle might formed at high molar fraction of alkyl benzene sulfonates.4)Intermolecular interaction between surfactin and cetyl trimethyl ammonium bromide(CTAB)in mixed micelles were studied by surface tension and fluorescence methods.Various parameters including interaction parameter(?m)in micelle and thermodynamic properties of mixed micelles formation have been determined.Synergism exits between anionic surfactin and cationic CTAB surfactants.The effort of surfactin participated in mixed micelle formation changes with mixing ratio of the two surfactants.The two surfactants combine more compactly and easily to form compact mixed micelles due to electrostatic attraction between the head groups with opposite charge as well as the hydrophobic interaction between the alkyl chains.The strongest interaction between surfactin and CTAB exhibited at a mole fraction of surfactin of 0.8.The results of fluorescence anisotropy and aggregation number indicate that the mixed system may be able to form bilayer aggregates and vesicles spontaneously.The results provide a basis for producing a preferable HABS for tertiary oil recovery.They also help us to understand the mechanism of interaction between surfactin and synthetic surfactants and provide a basis for application of surfactin in fields of oil recovery,daily-use chemical industry.Pharmaceutical industry and so on.