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Different analytical methods were utilized to investigate the mechanisms for wettability alteration of oil-wet sandstone surfaces induced by different surfactants and the effect of reservoir wettability on oil recovery. The cationic surfactant cetyltrimethylammonium bromide (CTAB) is more effective than the nonionic surfactant octylphenol ethoxylate (TX-100) and the anionic surfactant sodium laureth sulfate (POE(1)) in altering the wettability of oil-wet sandstone surfaces. The cationic surfactant CTAB was able to desorb negatively charged carboxylates of crude oil from the solid surface in an irreversible way by the formation of ion pairs. For the nonionic surfactant TX-100 and the anionic surfactant POE(1), the wettability of oil-wet sandstone surfaces is changed by the adsorption of surfactants on the solid surface. The different surfactants were added into water to vary the core surface wettability, while maintaining a constant interfacial tension. The more water-wet core showed a higher oil recovery by spontaneous imbibition. The neutral wetting micromodel showed the highest oil recovery by waterflooding and the oil-wet model showed the maximum residual oil saturation among all the models.

The dynamic interfacial tensions (IFTs) of enhanced oil recovery (EOR) surfactant/polymer/organic alkali systems against a homologous series of alkanes have been investigated by a spinning drop interfacial tensiometer. Two organic alkalis with different molecular sizes, ethanolamine (EA) and diethanolamine (DEA), two surfactants with high interfacial activity, heavy alkyl benzenesulfonate (HABS) and petroleum sulfonate (SLPS), and two kinds of polymers, partly hydrolyzed polyacrylamide (HPAM) and hydrophobically modified polyacrylamide (HMPAM), were employed to study the real mechanisms controlling the IFT behavior. The experimental results show that the addition of organic alkali may affect the dynamic IFTs of surfactant solutions through different mechanisms. First, the possible reaction of organic alkali with the oil-soluble components in industrial surfactants will influence the surface active spices at the interface and enhance the dynamic behavior. Second, the hydrophilic–lipophilic balance (HLB) of...

Synergism of water-soluble hydrophobically associating polyacrylamide (HA-PAM) with nonionic surfactant laurel alkanolamide (LAA) was investigated via the rheology, fluorescence spectroscopy and dissipative particle dynamics (DPD) simulation methods. The viscosity and elasticity of HA-PAM solutions increased in a large LAA concentration range, which was principally ascribed to the crosslinking effect of LAA by aggregating to the hydrophobic chains of HA-PAM molecules as confirmed by the DPD simulation and experimental results. The crosslinking effect was enhanced in the presence of an appropriate amount of electrolyte or with increasing temperature in the studied temperature range of 20–70 °C. Thus, the LAA not only significantly enhanced the salt resistance of HA-PAM but also retarded the decrease of the viscosity and elasticity of the HA-PAM solutions at high temperature. The HA-PAM/LAA binary systems exhibit great potential for application in tertiary oil recovery of oil fields with high salinity.

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.

Stimuli-responsive polymer brushes modified surfaces and binary polymer surfaces can be created on an initiator terminated substrate via surface initiated atom-transfer radical polymerization (SI-ATRP), in which the growth kinetics can be modulated by Cu(II) ratio. As stimuli-responsive brushes, many environmental triggers can drive their conformation change such as pH and salt concentration. The external-stimuli modulated reversible conformational changes of polymer brushes can influence the charge transport behavior investigated by electrochemistry method, which have potential applications in in situ switching ion permeability and charge transport. The charge transport of binary polymer brush can be switched on or off by different ion flexibly which is an electrochemical logic switch.

The interfacial activity of surfactants is an issue that attracts considerable attention. However, most of the literature focuses on pure surfactants, and the effect of impurities on surfactant activity remains an elusive puzzle in the understanding of structure–performance relationships. In this paper, the nonionic surfactant laurel alkanolamide (LAA) synthesized by a one-step method was found to decrease the oil–water interfacial tension to ultra-low values at low concentration without co-surfactants. LAA also had surprising oil phase adaptability, making it a perfect model not only to study the theoretical mechanism for obtaining ultra-low interfacial tension, but also for distinguishing the contribution of the molecular interfacial array behaviour of surfactants and concomitants (defined as the residual reactants and by-product) on the interfacial activity. The oil–water interfacial activity of LAA with or without concomitants was investigated experimentally and theoretically using dissipative dynamic simulation (DPD). The detailed molecular array behaviour of LAA and the concomitants at the oil–water interface was investigated by molecular dynamics (MD). The concomitants were found to coexist with LAA at the oil–water interface and distribute at different positions in the interfacial layer, resulting in the high interfacial activity and oil phase adaptability. The experimental results agree well with the simulation results. We hope our strategy can provide an avenue to understand the structure–performance relationship of surfactants at the molecular level and reveal an effective approach to obtaining ultra-low interfacial tensions with different oil phases.

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 counterion...

In the present work, the influences of different types of electrolytes on interfacial dilational properties of anionic surfactant sodium 4,5-diheptyl-2-propylbenzene sulfonate 377 and asymmetrical anionic Gemini surfactant C 12 COONa-p-C 9 SO 3 Na in the absence or presence of 1500 ppm partly hydrolyzed polyacrylamide were studied at decane–water interface, respectively, by means of interfacial tension relaxation measurements. The decay curves of interfacial tension were fitted by the summation of a number of exponential functions. The dilational elasticity ( ɛ r ) and dilational viscosity component ( ɛ i ) were calculated by Fourier transform and displayed as Cole–Cole plots (plotting ɛ i or ɛ i / ɛ 0 as a function of ɛ r or ɛ r / ɛ 0 respectively). The experimental results show that only single reorientation process dominates the interfacial properties in the presence of any electrolyte for 1 × 10 −6 mol L −1 377 solution, resulting form the more compacted film by electrostatic screening. On the other hand, the contribution of reorientation process at higher frequency decrease after the addition of NaCl and there exists no pure reorientation process in the presence of CaCl 2 or MgCl 2 for Gemini surfactant because of the slight increase of interfacial concentration due to larger molecular size and strong steric hindrance between alkyl chains. The addition of polymer can significantly modify the dilational properties of adsorbed surfactant layer due to the formation of mixed adsorption film through hydrophobic interaction between polymer chain and alkyl chain of surfactant molecule. The normalized Cole–Cole plots of surfactant-polymer films with different types of electrolytes show the similar characteristic in general and no pure reorientation process can be observed in any case.

A series of novel surfactants, sodium N-2-(alkylphenoxy)-tetradecanolytaurinates (12 + nB-T, where 12 means the carbon number of alkyl chain in the main chain and n is the carbon number of alkyl chains in the side chain attached to the phenoxyl group, n = 0, 2, 6) bearing identical polar groups, were designed and synthesized. The dilational properties of the three surfactants at the water–air and water–decane interfaces were investigated by drop shape analysis. The influences of oscillating frequency and bulk concentration on dilational properties were explored, and the effect of alkyl chain length in the side chain on interfacial behavior has been expounded. The longer alkyl chains in the side chains lead to a higher surface dilational elasticity at low bulk concentrations, owing to strong interaction among the longer hydrophobic alkyl chains. However, at high bulk concentrations, the longer the hydrophobic alkyl chain is, the easier the diffusion-exchange between the bulk and the surface becomes. As a r...

This present article employs four anionic Gemini surfactants with different spacer groups and investigates their physicochemical and aggregation properties. The critical micelle concentration (CMC), surface tension at CMC (γCMC) and C 20 of these surfactants have been investigated using the du Nouy ring method. The aggregation number (N) was determined with intrinsic fluorescence quenching method using pyrene as a fluorescence probe and benzophenone as a quencher. Results show that these anionic Gemini surfactants have lower CMC and C 20 values compared with those conventional ones and show higher surface activity. As expected, the spacer plays an important role in the aggregation properties of Gemini surfactants. Under experimental conditions, Gemini B–D with an alkoxylated group as spacer has a lower CMC and a higher aggregation number than Gemini A with methylene as spacer. For Gemini B–D, the CMC and aggregation number values decrease with the increasing flexible spacer length. The micropolarity also affects the aggregation of the present anionic Gemini surfactants. The micropolarity of micelle becomes low when the concentration of surfactants increases. Aggregation numbers of surfactants increase and fluorescence intensities decrease with the increasing concentration of NaCl. These results will help us to understand the relationship between the architectures of Gemini surfactants and their various properties in aqueous solution.

The microscopic flow mechanism of polymer flooding was examined using an industrial microfocus computerized tomography system. On the basis of scanned slices acquired in the process of water flooding and polymer flooding, three-dimensional visualization of oil and water distribution in different flooding conditions was achieved with a series of image processing methods, including pre-processing, interpolation, segmentation, and three-dimensional construction, which are effective techniques for both the qualitative description and the quantitative characterization of the microscopic flow mechanism. This study has confirmed the suggestion that the displacement efficiency of polymer flooding is higher than that of water flooding, and effectively revealed the microscopic mechanism of oil recovery in polymer flooding. The water/oil mobility ratio was improved after polymer flooding, which resulted in a break of the “equilibrium” flow field that was formed during water flooding and the redistribution of the regions of oil saturation. The remaining oil was flushed out as the result of the flow redirection and the viscoelastic effect of polymer flooding. Compared to water flooding, polymer flooding increased the microscopic sweep efficiency as well as the microscopic displacement efficiency, and thereby the ultimate oil recovery.