Weak Surfactant Research Articles

The Research on Weak Alkali ASP Compound Flooding System for Shengli Heavy Oil

In order to avoid the disadvantages caused by strong alkali used in enhanced oil recovery, sodium metaborate was compounded with nonionic surfactant nonylphenol polyoxyethlene polyoxypropylene ether sulfate and hydrolyzed polyacrylamide for the first time as a chemical displacement agent for Shengli heavy oil. The interfacial tension between crude oil and aqueous solutions, emulsification tests, microscopic displacement properties and sandpack flooding were investigated. It can be observed that the interfacial tension was reduced to ultra-low value due to the synergy effect between the weak alkali and surfactant. The microscopic displacement tests showed that there was an optimum surfactant concentration for alkali-surfactant flooding system to obtain larger sweep efficiency. And the recovery efficiency can be further increased by addition of hydrolyzed polyacrylamide. The oil recovery increased with the increasing of hydrolyzed polyacrylamide concentration. The newly designed compound system was proven to have the application potential on pilot tests. Key words : Weak alkali; Sodium metaborate; Compound flooding system; Nonylphenol polyoxyethlene polyoxypropylene ether sulfate; Heavy oil

Wet adhesion and adhesive locomotion of snails on anti-adhesive non-wetting surfaces.

Creating surfaces capable of resisting liquid-mediated adhesion is extremely difficult due to the strong capillary forces that exist between surfaces. Land snails use this to adhere to and traverse across almost any type of solid surface of any orientation (horizontal, vertical or inverted), texture (smooth, rough or granular) or wetting property (hydrophilic or hydrophobic) via a layer of mucus. However, the wetting properties that enable snails to generate strong temporary attachment and the effectiveness of this adhesive locomotion on modern super-slippy superhydrophobic surfaces are unclear. Here we report that snail adhesion overcomes a wide range of these microscale and nanoscale topographically structured non-stick surfaces. For the one surface which we found to be snail resistant, we show that the effect is correlated with the wetting response of the surface to a weak surfactant. Our results elucidate some critical wetting factors for the design of anti-adhesive and bio-adhesion resistant surfaces.

Interfacial tension between benzene and water in the presence of caprolactam

We studied the physical properties and the concentration profile of benzene+water+caprolactam mixtures near the fluid–fluid interface using self-consistent field (SCF) theory. This yields the interfacial tension which plays an important role in describing the stability of transient liquid droplets of one phase in the other. The studies were performed at a fixed temperature of 313K. Flory–Huggins binary interaction parameters and the compound lattice segment numbers are input parameters for the applied SCF theory. These parameters were derived from activity coefficient relations, which are used to describe experimental liquid–liquid and vapor–liquid phase equilibrium measurements. Using first principles, the benzene–water interface was studied and the resulting interfacial tension was found to be in agreement with experimental values. This study illustrates that caprolactam accumulates at the benzene–water interface, acting as a weak surfactant. The interfacial tension is also demonstrated to be affected by the caprolactam concentration and the SCF results are in fair agreement with the experimental observations.

Complexing a small interfering RNA with divalent cationic surfactants

Small interfering RNAs (siRNAs) are double strand RNA fragments of short sequence (∼20 bp). RNA interference came into focus only 13 years ago as a major biological breakthrough and, since then, many studies have described the involvement of siRNA in gene silencing. Application to gene therapy is extremely promising, provided that appropriate vectors are used. Optimising transfection efficacy strongly relies on the knowledge and tuning of physicochemical properties of transfection complexes, such as size, surface charge and internal interactions, which govern in vitro and in vivo stability. Here we report a study on siRNA complexation with micelles of two types of divalent cationic surfactants, i.e. three Gemini bis(quaternary ammonium) bromide with variable spacer length (12-3-12, 12-6-12, 12-12-12) and one weak electrolyte surfactant with a triazine polar head. The process of complex formation was followed by SANS, DLS and zeta potential. Charge density on micelles and counterion exchange were key factors in determining the extent of complexation, as it happens to polymer electrolytes interacting with micelles. A description of complex formation was given in terms of liquid–liquid micro-phase separation, due to internally structured coacervates progressively nucleating from the micelle solution upon siRNA addition. An affinity order between surfactants and siRNA could be established on the basis of the obtained results and their comparison.

Surfactant-Induced Postsynthetic Modulation of Pd Nanoparticle Crystallinity

Modulation of Pd nanoparticle (NP) crystallinity is achieved by switching the surfactants of different binding strengths. Pd NPs synthesized in the presence of weak binding surfactants such as oleylamine possess polyhedral shapes and a polycrystalline nature. When oleylamine is substituted by trioctylphosphine, a much stronger binding surfactant, the particles become spherical and their crystallinity decreases significantly. Moreover, the Pd NPs reconvert their polycrystalline structure when the surfactant is switched back to oleylamine. Through control experiments and molecular dynamics simulation, we propose that this unusual nanocrystallinity transition induced by surfactant exchange was resulted from a counterbalance between the surfactant binding energy and the nanocrystal adhesive energy. The findings represent a novel postsynthetic approach to tailoring the structure and corresponding functional performance of nanomaterials.

Surfactant effect on the formation of CuInSe2 nanowires in solution phase synthesis

Solution-phase synthesis of CuInSe2 nanowires without using metal nanocrystal catalysts has been demonstrated. The morphology of chalcopyrite CuInSe2 nanoparticles could be varied from spheres to highly anisotropic nanowires by varying the relative amount of strong and weak binding surfactants passivating the surface. For CuInSe2 nanowires, weakly binding dioctylphosphine oxide (DOPO) was found to be the key surfactant that enables the anisotropic 1-dimensional growth. Detailed analysis of the structure of the nanowires indicates that they grow perpendicular to (112) planes, with twinning around the growth axis by ∼60° rotation. The nanowires of CuInSe2 synthesized in this study exhibit saw-tooth surface morphology resembling a stack of truncated tetrahedra which show a continuous growth mechanism.

Comparative validation of the analytical models for the Marangoni effect on foam film drainage

The aim of this paper is to evaluate four of the well-known models for drainage of thin liquid films, containing non-ionic surfactants, by applying them to different types of draining foam films stabilized by either strong or weak non-ionic surfactants. The effect of non-ionic surfactants on the drainage of foam films under different conditions was studied. The following series of surfactants were employed: (1) methylisobutyl carbinol (MIBC), (2) Dowfroth 200, (3) pentaethyleneglycol monodecyl ether (C 10E 5), (4) pentaethyleneglycol monododecyl ether (C 12E 5), (5) hexaethyleneglycol monododecyl ether (C 12E 6), (6) octaethyleneglycol monododecyl ether (C 12E 8) and (7) tetraethyleneglycol monooctyl ether (C 8E 4). The experimental ‘thickness’ vs ‘time’ dependences were processed with four kinetic models: (1) the model developed by Scheludko on the basis of the Stefan–Reynolds lubrication theory (Scheludko model); (2) the model of Radoev, Dimitrov and Ivanov for foam films confined between partially mobile planar gas–liquid surfaces (RDI model); (3) the model of Ruckenstein and Sharma for foam films with surfaces wrinkled by capillary waves (RSh model); (4) the model of Manev–Tsekov–Radoev for foam films with surfaces corrugated by quasi-stationary inhomogeneities (MTR model). A systematic validation based on the statistical level of uncertainty of the model predictions, as compared to the experimental results was preformed. The test on the model kinetic equations confirmed their validations reported in the literature. In addition, cases in which none of the models is valid were identified as well. Ultimately, it was concluded that thin film drainage is a complex phenomenon, which should be studied further by different experimental techniques and modelling approaches.

Effects of various imidazole-based weak bases and surfactant on the conductivity and transparency of poly(3,4-ethylenedioxythiophene) films

Poly(3,4-ethylenedioxythiophene) (PEDOT)-based conductive thin films with improved transparency and surface resistance can be prepared by using adequate weak bases and non-ionic surfactants. Among the imidazole-based weak bases, 2-ethyl-4-methyl-substituted imidazole showed the best performance in terms of surface resistance and transparency. It is speculated that 2-ethyl-4-methyl-imidazole causes reduced particle size because polymerization kinetics are retarded by the electron donating effect of ethyl and/or methyl groups in the imidazole ring. Addition of Triton X-100 may stabilize nanoscopic PEDOT particles in the coating solution resulting in low surface resistance (172 Ω/□) and enhanced transparency (>90%) of the PEDOT film.

Anomalous thickness variation of the foam films stabilized by weak non-ionic surfactants

The constant thickness ( H) of metastable free films of various non-ionic surfactant solutions was measured at surfactant concentrations less than the critical micelle concentrations or solubility limits with fixed 5 × 10 - 5 M sodium chloride (NaCl) serving as the background electrolyte. The surfactants include n-pentanol, n-octanol, methyl isobutyl carbinol (MIBC), polypropylene glycol (PPG-400), tetraethylene glycol monooctyl ether (C 8E 4), and tetraethylene glycol monodecyl ether ( C 10 E 4 ). H was interferometrically measured. For each surfactant in this study, the H-versus-surfactant-concentration curve finds a peak at a concentration around 5 × 10 - 6 –1 × 10 - 5 M and a valley at a higher concentration. The measured H values were compared to those predicted from the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, which considers solely the contribution from electrostatic double-layer repulsion with van der Waals attraction being neglected in the present work. In determining the double-layer repulsion, the ionic strength was determined from the electrolytic conductivity measurement of the film-forming solutions and the surface potential was estimated from the ζ -potential measurement of air bubbles. It was found that the DLVO theory failed to explain the thickness variance with surfactant concentration, implying that additional non-DLVO attractive forces might be required to explain the experimental results. Finally, the possible origins of these attractive forces were discussed.

Characterization of fatty acids and proteins associated with the xanthophyll-enriched membrane fraction isolated from the thylakoid membranes of irradiance-stressed Dunaliella salina

It has been previously reported that a considerable amount of lutein and zeaxanthin could be fractionated, upon mild detergent treatment, from the thylakoid membranes of irradiance-stressed unicellular green alga, Dunaliella salina, into a yellow pellet fraction. Such membrane pellet was found to be devoid of chlorophylls and any known proteins of photosynthesis but rather contained a significant amount of unknown polypeptides. It was speculated that this xanthophyll-rich membrane pellet might originate from incomplete solubilization of the photoinhibited thylakoids by weak surfactants, due to extra rigidity imposed by the xanthophylls being directly imbedded into the lipid bilayer. In this study, we further characterized this membrane fraction by studying its associated proteins and fatty acid composition. Analysis by gas chromatography–mass spectrometry indicated that this yellow pellet membrane was enriched in saturated fatty acids, supporting the rigidity notion of the pellet. Protein identification by MALDI-TOF MS further revealed that at least 20 water-soluble proteins were found in association with this pellet. These proteins may originate from unspecific contamination of abundant polypeptides co-precipitated with the membrane upon fractionation. Possible explanations regarding the nature of this xanthophyll-rich membrane are also discussed.

Aggregation of humic acid in solution: Contributions of different fractions

The role of lipid components in the aggregation of several humic acids isolated from different sources was investigated using surface tensiometry. A combination of aqueous alkaline and organic solvent extractions was used to isolate two humic-like fractions (HA 1 and HA 2) and one lipid-like fraction from each humic acid. Fraction HA 1 represents approximately two-thirds of the total organic carbon of the original humic acid and under alkaline conditions is a weak surfactant that lowers the surface tension of water by only a small amount. The HA 2 fraction represents up to one-third of the humic acid and significantly lowers the surface tension of water. It is also intimately associated with the lipid fraction. Unlike the original humic acid samples, HA 2 does not show micelle-like aggregation over the concentration range studied. Aggregate formation is discussed as an emergent characteristic that results from the interaction of the humic acid’s components with the lipid components serving a facilitative role.

Aqueous-biphasic hydroformylation of alkenes promoted by “weak” surfactants

The aqueous-biphasic hydroformylation of higher alkenes catalyzed by Rh/TPPTS has been carried out in the presence of imidazolium, pyridinium and triethylammonium salts. High reaction rates are achieved with imidazolium and triethylammonium salts provided that their alkyl “tail” is ≥C8. Fast and complete phase separation, and good retention of the metal in the aqueous phase could be achieved with an octyl “tail”. Imidazolium salts were found to give the highest rate enhancement. The nature of the anion showed a moderate influence on the reaction. Evidence suggests that the additive can act as weak surfactant allowing emulsions to be formed and broken by simply switching the stirring on and off.

Orientation‐Selective Incorporation of Transmembrane F0F1 ATP Synthase Complex from Micrococcus luteus in Polymer‐Supported Membranes

We report the vectorial incorporation of a highly asymmetric F0F1 ATP synthase complex from Micrococcus luteus into polymer-supported membranes. Dynamic light scattering and cryo electron microscopy confirm that the use of weak surfactants (bile acid) allows for the non-disruptive protein incorporation into lipid vesicles. Spreading of vesicles with ATP synthase onto a cellulose support results in a homogeneous distribution of proteins, in contrast to a patchy image observed on bare glass slides. The orientation of ATP synthase can be identified using an antibody to the ATP binding site as well as from topographic profiles of the surface. The method to "align" transmembrane proteins in supported membranes would open a possibility to quantify protein functions in biomimetic model systems.

Self-assembling properties of malonamide extractants used in separation processes

A review of the four microstructures present in oil phases of malonamide extractants used for nuclear fuel reprocessing is presented in relation with the extraction properties and the third phase formation. Due to their surface active properties, extractants can be considered as a weak surfactants and are organised into reverse micelles interacting through an attractive potential. The Van der Waals attractions between the cores of reverse micelles are the key parameters for understanding “third phase” formation. Extractant solutions are similar to reverse microemulsions and the stability rules known in the field of microemulsions can be applied. In some cases, micelles are transformed into a regular molecular solution by modest heating. Apart from micellar and regular solutions, two new modes of association of extractant molecules have been identified. Networks of H-bounds are obtained when “modifiers” such as octanol are added by formulators in order to improve stability range. Microphase separation in a more crystalline phase may be obtained by increasing extractant and/or ion concentrations.

Novel nanocomplexes of hyperbranched poly(ethyleneimine), and dodecyl maltoside.

The aqueous complexes of poly(ethyleneimine) (PEI), sodium dodecyl sulfate (SDS) and dodecyl maltoside (C12G2) have been studied under dilute conditions using dynamic light scattering, electrophoretic mobility, surface tension and pH measurements. According to the surface tension data the complexation between PEI and C12G2 can be neglected while a strong interaction was detected between PEI and SDS. The charged nature and size of the PEI-SDS-C12G2 complexes vary in a similar manner with SDS concentration as for the PEI-SDS systems. At large excess of SDS a kinetically stable colloid dispersion of the compact PEI-SDS-C12G2 particles forms. The electrophoretic mobility measurements indicate that the charge reversal of the PEI molecules occurs at lower SDS concentrations in the presence than in the absence of dodecyl maltoside. The enhanced charge inversion of PEI affords a significant extension of the concentration range with kinetically stable dispersion of the polyelectrolyte-surfactant nanoparticles compared with the PEI-SDS system. The pH of the PEI-SDS-C12G2 mixtures also reveals a peculiar dependence on the surfactant concentration. These latter findings are explained by the synergistic binding of the ionic and non-ionic surfactants to both the uncharged and charged amine groups of the PEI. It can be concluded that the addition of sugar surfactants is an efficient way to increase the kinetic stability and manipulate the pH of the mixtures of oppositely charged weak polyelectrolytes and surfactants.

Dimers of the Neuropeptide Y (NPY) Y2 Receptor Show Asymmetry in Agonist Affinity and Association with G Proteins

In conditions precluding activation of G proteins, the binding of agonists to dimers of the neuropeptide Y (NPY) Y2 receptor shows two components of similar size, but differing in affinity. The dimers of all NPY receptors are solubilized as ∼ 180-kDa complexes containing one G protein α β γ trimer. These heteropentamers are stable to excess agonists, chelators, and alkylators. However, dispersion in the weak surfactant cholate releases ∼ 300-kDa complexes. These findings indicate that both protomers in the Y2 dimer are associated with G protein heterotrimers, but the extent of interaction depends on affinity for the agonist peptide. The G protein in contact with the first-liganded, higher-affinity protomer should have a stronger interaction with the receptor and a larger probability of activation.

Synthesis of Tubular Gold and Silver Nanoshells Using Silica Nanowire Core Templates

We report the synthesis of tubular gold and silver nanoshells on silica nanowire core templates in solution. Silica nanowires were synthesized and characterized with optical and NMR methods. Gold nanoparticle seeds (2 to 3 nm) with weak repulsive surfactants such as tetrakis-hydroxymethyl-phosphonium chloride (THPC) were conjugated to the surface of these nanowires. A regrowth process was initiated from these nanoparticles on the surface of the silica nanowires dispersed in gold or silver stock solutions in the presence of reducing agents. Micrometers-long gold and silver tubular nanoshells (80-150 nm o.d.) were made, fully covering the silica nanowires.

Wetting alteration of mica surfaces with polyethoxylated amine surfactants

Characterization of reservoir wettability is an important part of assessment of potential oil recovery. Oil-based drilling fluids include surfactants, which can alter the wettability of mineral surfaces. Cores exposed to these fluids may not reflect the true wettability of the reservoir materials. The focus of this study was to observe wettability changes induced by adsorption and removal of surfactants of known structure on mica surfaces using tools that are applicable to studies of wetting alteration by crude oil components. The surfactants used were polyethoxylated coconut and tallow amines with chain lengths of 12 and 18 carbons and head groups consisting of two to five ethoxy groups. Mica was exposed to decane solutions of the surfactants. The treated mica was characterized macroscopically using contact angle measurements and microscopically using atomic force microscopy (AFM). Upon exposure to the surfactant solutions, the mica became oil-wet (∼ 170° for both advancing and receding conditions). AFM examination of similarly treated surfaces imaged in air revealed surfactant layers that were easily disrupted or surfaces that showed no surfactant at all. Contact angles were in the intermediate to water-wet range if the mica samples were removed from the surfactant solution, rinsed with non-aqueous solvents, and submerged in decane for measurements of water/decane contact angles. These results suggest only weak surfactant adsorption occurred from non-aqueous solutions. Differences among the structures tested were greater for increased levels of ethoxylation; differences due to hydrocarbon chain length were negligible. Stronger adsorption, higher contact angles, and more stable surfactant layers could be demonstrated when mica was exposed to aqueous solutions after surfactant sorption, depending on the pH of the aqueous phase. Low pH conditions that promote protonation of the surfactants' amine head group produced the greatest wetting alteration. Above a pH of 8 or 9, no surfactant remained adsorbed on mica surfaces.

Two-dimensional modeling of the effects of insoluble surfactant on the breakup of a liquid filament

Breakup of surfactant-laden liquid jets has received increasing consideration during the last few years because of its diverse applications, but theoretical studies have been largely restricted to evolution equations based on one-dimensional flow assumptions. Here, a fully two-dimensional finite element algorithm was used to solve the set of equations describing the dynamics of a Newtonian liquid filament covered with an insoluble surfactant in order to provide a better understanding of the underlying physical principles governing the formation of satellite drops. Results indicate that for a viscous liquid jet, formation of satellite drops between main drops is favored by the addition of surfactants. This effect is lessened, and even eliminated, by either decreasing the surfactant strength or increasing the surfactant diffusivity. On the other hand, low-viscosity liquid jets form satellite drops regardless of the presence of surfactant, but the addition of surfactant can either reduce or increase the size of the satellite formed. Reduction of the size of the satellite drop is favored by the addition of weak surfactants, a result that is in agreement with previous one-dimensional flow analyses. Conversely, addition of strong surfactants of low surface diffusivity increases the size of the satellite drop formed due to Marangoni stress-induced reversal of the capillary flow. The detailed information provided by the two-dimensional model has enabled a better understanding of the competition between viscous, inertia and capillary forces during jet breakup, and of how the competition between them changes due to the presence of the surfactant. This understanding can help in the rational design of systems such as spray, atomization, and jet printing to prevent the formation of satellite drops.

Scaled interfacial activity of proteins at a hydrophobic solid/aqueous‐buffer interface

Contact-angle goniometry confirms that interfacial energetics of protein adsorption to the hydrophobic solid/aqueous-buffer (solid-liquid, SL) surface is not fundamentally different than adsorption to the aqueous-buffer/air (liquid-vapor, LV) interface measured by pendant-drop tensiometry. Adsorption isotherms of 9 globular blood proteins with molecular weight (MW) spanning from 10 to 1000 kDa on methyl-terminated self-assembled monolayer surfaces demonstrate that (i) proteins are weak surfactants, reducing contact angles by no more than about 15 degrees at maximum solution concentrations ( approximately 10 mg/mL); (ii) the corresponding dynamic range of spreading pressure Pi(a) < 20 mN/m; and (iii) the maximum spreading pressure Pi(max) (a) for these diverse proteins falls within a relatively narrow 5 mN/m band. As with adsorption to the LV interface, we find that concentration scaling substantially alters perception of protein interfacial activity measured by Pi(a). Proteins appear more similar than dissimilar on a weight/volume basis whereas molarity scaling reveals a systematic ordering by MW, suggesting that adsorption is substantially driven by solution concentration rather than diversity in protein amphilicity. Scaling as a ratio-to-physiological-concentration demonstrates that certain proteins exhibit Pi(max)(a) at-and-well-below physiological concentration whereas others require substantially higher solution concentration to attain Pi(max)(a). Important among this latter category of proteins is blood factor XII, assumed by the classical biochemical mechanism of plasma coagulation to be highly surface active, even in the presence of overwhelming concentrations of other blood constituents such as albumin and immunoglobulin that are shown by this work to be among the class of highly surface-active proteins at physiologic concentration. The overarching interpretation of this work is that water plays a dominant, controlling role in the adsorption of globular-blood proteins to hydrophobic surfaces and that energetics of hydration control the amount of protein adsorbed to poorly water-wettable biomaterials.