The dynamic interfacial tension (IFT) of ethoxylated fatty acid methyl ester solutions against n-alkanes, kerosene, and diluted heavy oil have been investigated by spinning drop interfacial tensiometry. The influences of ethylene oxide (EO) groups and alkyl chain length on IFT were investigated. The experiment results show that the water solubility decreases with an increase in alkyl chain length or a decrease in EO groups. The ability to lower the interfacial tension against hydrocarbons improves with both increasing alkyl chain length and EO group at the best hydrophilic-lipophilic balance, which can be attributed to the enhancement of the interfacial hydrophobic interactions and the rearrangement of interfacial surfactant molecules. The mixed adsorption of surfactant molecules and surface-active components may reduce IFT to a lower value. C18=E3 shows the best synergism with surface-active components. However, the IFT values against pure crude oil are obviously higher than those against hydrocarbons, which may be caused by the nature of heavy oil.

•An increase of alkyl chain length improves the surface activity of di-substituted alkyl benzene sulfonates.•The active components in daqing crude oil form mixed adsorption films with di-substituted alkyl benzene sulfonates.•The properties of surfactant films are dominated by the intermolecular interactions at kerosene/water interface.•The tight surfactant film will be weakened by the insertion of active components at crude oil/water interface.In this research, the interfacial properties of di-substituted alkyl benzene sulfonates at kerosene/water and daqing crude oil/water interfaces have been studied by interfacial tension and interfacial dilational rheological measurements. The experimental results show that the di-substituted alkyl benzene sulfonates can obviously lower the interfacial tensions of kerosene/water and daqing crude oil/water interfaces. The mixed adsorption of active components with sulfonate molecules will reduce or improve interfacial tension at low or high surfactant concentration respectively. Moreover, the adsorption layers formed by di-substituted alkyl benzene sulfonate molecules shows high value of modulus at kerosene/water interface due to the strong interactions among long alkyl chains. However, the mixed adsorption of active components with sulfonate molecules will destroy the tight arrangement of surfactant molecules and result in the obvious decrease of modulus. The possible mechanism has been proposed and ensured by modulus-interfacial pressure curves.The mixed adsorption of crude oil components with di-substituted alkyl benzene sulfonate molecules will destroy the tight arrangement of surfactant molecules.Download high-res image (98KB)Download full-size image

The stability of foams in the presence of oil is a crucial factor for foam displacement process in enhanced oil recovery. After the test of foam stability in the presence of oil of the mixtures of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (C12TAB), “catanionic” surfactant mixtures are proposed as a novel agent to enhance the oil resistance of foam. Based on the investigations of the foam evolution and the interfacial properties, the mechanisms are demonstrated by means of approaches of multiple light scattering and interfacial dilational rheological experiments. Because of the electrostatic attraction between molecules with opposite charges, catanionic mixtures are highly close-packed and form dense adsorption layers, which possess high modulus. So when oil–aqueous and gas–aqueous interfaces are approaching each other, strong pseudoemulsion films are formed. The compact adsorption layers also inhibit the diffusion exchange between the interface and the bulk, and this is the key factor to decrease the interaction between the gas–aqueous and oil–aqueous interfaces of the pseudoemulsion film. These properties increase the enter barrier of the oil droplets to the film surface.

•There is a competition between anionic surfactants and quartz surface in attracting cationic surfactants.•C12TAB molecules are constrained by SDS in solution and hardly adsorb on quartz surface.•SDDS and DAS fail to restrain the adsorption of C12TAB on quartz surface.•SDDS and DAS mixed adsorb with C12TAB on quartz surface, resulting in stronger hydrophobic modification.The adsorption behaviors of dodecyl trimethyl ammonium bromide (C12TAB) and the catanionic mixtures of C12TAB with sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (SDDS) and sodium dodecanoate (DAS) on quartz surface have been investigated. Physicochemical parameters such as the critical micelle concentration (CMC), surface tension, contact angle, adhesional tension and work of adhesion have been estimated. At the interface of quartz and aqueous solution of catanionic mixture, there is a competition between anionic surfactants and quartz surface in attracting cationic surfactants. SDDS and DAS fail to inhibit the adsorption of C12TAB because of the smaller size and less negative charge of the head-groups, even the amount of anionic surfactants well surpasses that of C12TAB. Instead the anionic surfactants are dragged by cationic surfactants to quartz surface and form a mixed monolayer on the quartz surface. The insert of anionic surfactants reduces the repulsion between the cationic molecules and results in closer packing of molecules in adsorption layers. Thus, SDDS-C12TAB and DAS-C12TAB have displayed stronger hydrophobic modification at quartz surface than pure C12TAB. However, the electrostatic attraction between excessive SDS and C12TAB is strong enough to constrain C12TAB and decreases the adsorption on quartz surface. Only a small amount of catanionic complexes with the structure like zwitterionic surfactant adsorb on quartz through the interaction between the positive sites of surfactant complexes and negative sites of quartz. Over CMC, bilayers are formed on quartz surface in the systems of SDDS-C12TAB and DAS-C12TAB, while micelle structures are adsorbed on quartz surface for SDS-C12TAB.For SDDS-C12TAB and DAS-C12TAB, the bilayer will be formed after CMC, while the aggregations of SDS-C12TAB may be formed on quartz.

•Catanionic surfactant mixtures are closely-packed at oil-aqueous interface and the adsorption layer has displayed strong viscoelasticity.•The ratio of anionic/cationic surfactants on the adsorption layer is independent with the ratio in the bulk.•The SDS-C12TAB mixture adsorption layers arrange more closely and possesses higher elasticity than SDDS-C12TAB and DAS-C12TAB.•Long alky chain makes the molecular motion, orientation and rearrangement more difficult and slows down the relaxation processes.Catanionic surfactant mixtures have shown advantages in many applicable aspects for strong synergetic behavior. In the present work, the adsorption behaviors of catanionic mixtures at oil-aqueous interface have been studied by means of interfacial tension measurements and interfacial dilational rheological experiments. Because of the electrostatic attraction, catanionic mixtures are tightly packed: at low concentration, catanionic surfactant mixtures pack as co-surfactant like Gemini, while at high concentration (≥CMC), catanionic mixtures generate closely-packed network adsorption layers at oil/aqueous interfaces, which are strongly viscoelastic. The interfacial properties indicate the ratio of anionic and cationic surfactant at interface is independent with the ratio in the solution but depends on the molecular structure of surfactants. The interaction between anionic and cationic follows the order: SDS-C12TAB > SDDS-C12TAB > DAS-C12TAB. Therefore the adsorption layer of SDS and C12TAB packs more closely at the interface and possesses higher elasticity. As to the hydrophobic groups, the increase of alkyl chain length enhances the hydrophobic force, but makes the molecular motion, orientation and rearrangement more difficult. These results provide basis for the design of catanionic mixtures to regulate and control the interfacial properties to adapt to the different applications.Surfactants with opposite charge pack as co-surfactant at low concentration, while catanionic mixtures generate closely-packed adsorption layers at oil/aqueous interfaces at high concentration.

The contact angle measurements for the aqueous solutions of two pairs of zwitterions on quartz surfaces have been investigated by the sessile drop analysis. The different physicochemical parameters such as the critical micelle concentration (CMC), surface tension, contact angle, surface excess on air–liquid and solid–liquid interfaces and work of adhesion have been estimated. The obtained results show that the contact angle of surfactants such as alkyl carboxylbetaine (ACB) and ditolyl substituted alkyl carboxylbetaine (BCB) remains almost constant in a wide range of surfactant concentration and increases gradually above CMC, which are quite different from traditional surfactants reported in the literature. Surfactants with bigger polar groups have a more steric effect on the quartz surface and the contact angle remains relatively unchanged. Moreover, an increase in quartz–liquid interfacial tension (γSL) has been observed due to the adsorption of four zwitterionic surfactants. Especially for ACB and BCB, at the surfactant concentrations higher than 5 × 10−5 mol L−1, a moderate increase in the interfacial tension of the quartz–liquid is observed, which suggests that ACB and BCB can form a saturated adsorption film briefly on the quartz surface and then adsorb again. However, the addition of alkyl sulfobetaine (ASB) and ditolyl substituted alkyl sulfobetaine (BSB) after CMC cannot adsorb on the quartz surface again due to the steric effect of bigger polar groups.

The effects of acidic components and asphaltenes on the dilational rheological properties of hydrophobically modified polyacrylamide (APP5) have been measured as a function of the time, frequency, bulk concentration, and interfacial pressure by means of a drop shape analysis method. It is established that acidic components and asphaltenes play an important role on the interfacial properties of the APP5/crude oil component mixture at water–kerosene interface. With the addition of acidic components, the dilational modulus of the mixture not only increases with time but is also higher at low concentrations and runs through a maximum at a lower concentration compared to pure APP5. Also, the phase angle of APP5/acidic components is lower compared to pure APP5. The results indicate that the appearance of more elastic films because of the mixed adsorption of acidic components and APP5 molecules. The addition of asphaltenes does not influence the interfacial properties of APP5 at high APP5 concentrations. However, one can observe changes of the interfacial tension and the dilational modulus with the addition of asphaltenes at lower APP5 concentrations. It can be concluded that the behaviors of interfacial layers of the APP5/asphaltene mixture are controlled by APP5 molecules in competition with the asphaltenes at the interface.

•The dynamic phase angle of C12BExCB film decreases with ageing time.•The dilational modulus passes through a plateau value with the increasing concentration.•The exchange between the interface and the sub-layer plays a crucial role for C12BExCB film.•The interfacial viscoelasticity of CyBE2CB film with different alkyl chain can support above mechanism strongly.The interfacial dilational rheological behaviors of four zwitterionic surfactants with benzene ring and polyoxyethylene group, p-(n-lauryl)-benzyl polyoxyethylene ether carboxybetaine C12BExCB (x = 0, 1, 2, 3), were investigated via the drop shape analysis method. The influences of time, oscillating frequency and bulk concentration on dilational properties were explored. The experimental results show that the number of ethylene oxide groups is one of the principal factors to control the interfacial film. The dilational properties of C12BExCB are quite different from those of common surfactants: the phase angle decreases with aging time, the slope of the logε − logω curve and phase angle of C12BExCB decrease in a wide concentration range, and the dilational modulus of C12BExCB passes through a plateau value with the increasing concentration for surfactant with more ethylene oxide groups. These phenomena become more and more apparent with increasing ethylene oxide groups and it cannot be attributed to the diffusion-exchange process between the bulk and the interface. It is reasonable to consider that ethylene oxide groups are flexible and can be compressed and expanded, just like a spring. The compression and expansion of the ethylene oxide groups in the interfacial layer and the exchange between interface and sub-layer play a crucial role for C12BExCB. Possible schematic diagrams of adsorbed molecules with time and concentration at the water–decane interface are proposed. The results of static modulus measurements and dynamic interfacial viscoelasticity for CyBE2CB (y = 8, 10, 12) with different length of hydrophobic chain can support our provided mechanism strongly.The exchange of ethylene oxide groups between the interface and the sub-layer plays a crucial role for the nature of C12BExCB film.

•C12E3 will reduce IFT to ultralow value for C12EO3C solution with Na+.•Both synergism and antagonism can be observed in mixed solutions with Mg2+.•The effect of Ca2+on IFTs is similar to that of Mg2+.•The hydrophilic–lipophilic balance plays the dominate role for compact adsorption films.•The mixed adsorption mainly controls the nature of loose interfacial films.The influences of nonionic surfactant on interfacial properties of anionic–nonionic surfactant against alkanes are studied by measuring the dynamic interfacial tension (IFT). The surfactants chosen are fatty alcohol polyoxyethylene carboxylate (C12EO3C) and fatty alcohol polyoxyethylene (C12E3) with various counterions, Na+, Mg2+, and Ca2+. On the basis of our experimental results, one can find that the addition of nonionic surfactants C12E3 could achieve an ultralow IFT value at some specific alkane carbon numbers under NaCl condition and the obvious synergistic effect on reducing IFT can be observed during all experimental alkane carbon numbers. However, for MgCl2 systems, the ultralow IFT values can be achieved by pure C12EO3C solutions and one can observe synergistic effect and antagonistic effect on IFTs at higher and lower alkane carbon numbers respectively by adding nonionic surfactant. On the other hand, for CaCl2 systems, the addition of 0.05% C12E3 shows the same influence on the IFTs as that of NaCl systems, while the similar effect as that of MgCl2 systems will be observed when adding 0.1% C12E3. An interfacial model combined two mechanisms, controlling hydrophilic–lipophilic balance and forming mixed adsorption film, responsible for varying IFT has been provided based on the difference of ion radius. By adding nonionic surfactant, the mechanisms of forming mixed adsorption film and controlling hydrophilic–lipophilic balance play crucial roles in effecting IFTs for NaCl systems and MgCl2 systems, respectively. Moreover, for CaCl2 systems, the responsible mechanism of forming mixed adsorption film will change into controlling hydrophilic–lipophilic balance with the increase of nonionic surfactant concentration.Graphical abstractDifferent mechanisms are responsible for the variations of IFTs of mixed surfactant solutions with Na+ and Mg2+ respectively.

Alkyl ether carboxylate is one type of surfactant that can produce ultralow interfacial tension (IFT) under high-salinity and high-temperature conditions. In this paper, the influence of counterions on dynamic IFTs of fatty alcohol polyoxyethylene carboxylate (C12EO3C) against alkanes has been studied. The effect of the temperature on the IFT has been investigated. On the basis of our experimental results, one can find that the NaCl concentration has little effect on the IFT, while divalent ions can reduce the IFT to an ultralow value. With the increasing CaCl2 or MgCl2 concentration, dynamic IFT passes through a minimum at a particular salt concentration (“V” shape). Moreover, the stable value of IFT achieves an ultralow value and also passes through a minimum at the same salt concentration. MgCl2 has a stronger tendency to achieve ultralow IFT than that of CaCl2, while the addition of CaCl2 has a stronger tendency to partition surfactant molecules to the oil phase. Ultralow IFT could also be achieved by improving the temperature because of the enhancement of oil solubility of the surfactant. An interfacial model combining two mechanisms, partitioning the surfactant into the oil phase and decreasing the charge repulsive force between interfacial surfactant molecules, responsible for the effect of the electrolyte on dynamic IFT has been provided. All experimental results above can be explained well. Our studies are of great significance in designing ultralow IFT formulation for the reservoir in a high temperature and with high-salinity formation water.

A series of anionic gemini surfactants called (oligooxa)-α,ω-bis(m-alkylbenzene sulfonate) with different length in spacer and in hydrophobic chain, C8ExC8 (x = 1, 2, 3, 4, 8) and CnE4Cn (n = 8, 10, 12), have been synthesized from 4-n-alkylphenol and their basic physicochemical properties are investigated. The results indicate that they are different from cationic gemini surfactants called (oligooxa)alkanediyl-α,ω-bis(dimethyl-dodecylammonium bromide), 12-CH2CH2(EO)s-12, in the literature. As the number of oxyethylene segments increases, the cmc (critical micelle concentration) decreases initially and then increases, and the surface area per molecule decreases initially and then tends to a constant value of approximate 1.30 nm2. Both of the breakpoints appear at number 4 of oxyethylene segments in the spacer. It is confirmed that the hydrophilic spacer with oxyethylene moieties is not fully extended at the air–water interface. With increasing spacer length, the spacer becomes sufficiently flexible to adopt a particular conformation with a loop at the water side of the air–water interface. The fluorescence data show that the micropolarity increases little from C8E1C8 to C8E4C8 and decreases obviously when x changes from 4 to 8. In addition, the plot of the logarithm of the cmc against the alkyl chain length for CnE4Cn shows a linear decrease with the increase in chain length. The micropolarity of the gemini surfactants (CnE4Cn) decreases with an increase in the alkyl chain length (n from 8 to 12).

The dilational properties of anionic gemini surfactants (oligooxa)-α,ω-bis(m-octylbenzene sulfonate) (C8ExC8) with polyoxyethylene spacers at the water−air and water−decane interfaces were investigated via the oscillating barriers method. The influences of oscillating frequency and bulk concentration on dilational properties were explored. The interfacial tension relaxation method was employed to obtain dilational parameters in a reasonably broad frequency range. The experimental results show that the number of ethylene oxide groups is one of the principal factors to control the nature of the interfacial film. With an increase of ethylene oxide groups, the dilational modulus of C8E8C8 shows two maxima with the increasing concentration. Furthermore, the dilational moduli at the water−decane interface are remarkably lower than those at the water−air interface for C8E1C8 and C8E4C8, while the dilational modulus at the water−decane interface is close to that at the water−air interface for C8E8C8, which indicates that the structure of the adsorption sublayer plays a more important role. Possible schematic diagrams of adsorbed molecules with different polyoxyethylene spacers at the water−air and water−decane interfaces are proposed. The results of relaxation experiments and Cole−Cole plots can support our provided mechanism strongly.

A novel double chained amphiphile, N-(α-4-hexylphenoxy)-lauroyltaurate (abbreviated as 10 + 6B-T), has been synthesized. The structures of main intermediate products and the title product were characterized by 1H NMR. The new amphiphile shows high surface activity. The critical micelle concentration (cmc), which is 1.1 × 10−5 mol/L, is much lower than that of conventional double chained surfactants, such as sodium bis(2-ethylhexyl)sulfosuccinate (AOT).

New nonionic–anionic surfactants of sodium straight chain alkyl benzyl alcohol homogeneous polyoxyethylenated propane sulfonates (ABEPS) were synthesized by the reaction of long chain alkyl (octyl, decyl and lauryl) benzyl chlorine with tri(ethylene glycol), followed by the reaction with 1,3-propane sultone. The physicochemical properties of ABEPS (e.g. Krafft temperature and equilibrium surface tension) have been measured. ABEPS shows favorable solubility, and all of the Krafft temperatures are below 0 °C. With increasing alkyl chain length, the critical micelle concentration (CMC), surface tension at CMC (γCMC) and surface area per molecule (Amin) of ABEPS decrease, and the efficiency in reducing surface tension (pC20) and adsorption at the air/water interface relation to micellization (CMC/C20) increase clearly. Compared with fat alcohol ether sulfates with an analogous number of carbon atoms in hydrophobic group, the values of pC20 and CMC/C20 for ABEPS were more predominant. Moreover, these surfactants in the article show the character of both nonionic and ionic surfactants due to its particular molecular structure.