Formation Of Wormlike Micelles Research Articles

Unusual pH-responsive fluid based on a simple tertiary amine surfactant: the formation of vesicles and wormlike micelles

A novel pH-responsive viscoelastic micellar system was prepared by N,N-dimethyl oleoaminde-propylamine without the addition of hydrotropes. The micellar system undergoes a gradual transition from vesicles to spherical micelles to wormlike micelles by adding an HCl solution. Rheology, Cryo-TEM and dynamic light scattering (DLS) results revealed that the pH-responsive flow behavior is attributed to the microstructural transition among the spherical micelles, vesicles and worm-like micelles. In this paper, we found out that a vesicle is extremely pH sensitive because the degree of protonation and the concentration of Cl− strongly affect the pH areas which could form worm-like micelles. The notable advantages of vesicles and worm-like micelles can be utilized to prepare pH-responsive viscoelastic fluids in the desired pH areas.

Effect of Molecular Parameters on the Architecture and Membrane Properties of 3D Assemblies of Amphiphilic Copolymers

Reliable prediction of the 3D structure of self-assembled amphiphilic copolymers is essential for applications in which specificity has to be carefully controlled, as for example in nanomedicine. Since supramolecular assemblies are strongly affected by the chemical nature of block copolymers and the preparation methods, it is essential to understand the influence of such parameters on the self-assembly process. We have now successfully synthesized a library of amphiphilic block copolymers, poly(dimethylsiloxane)-block-poly(2-methyl-2-oxazoline) (PDMS-b-PMOXA), and investigated the molecular parameters and self-assembly conditions that generate a specific architecture in particular polymersome. We found that 3D assemblies are strongly affected by the preparation method, but not by the initial concentration of block copolymer and solution pH. The phase diagrams of self-assembly behavior show a strong influence of the hydrophilic to hydrophobic ratio (fPMOXA), and the molecular mass of each block. In particular, the formation of polymersomes was possible only for block copolymers with high molecular mass PDMS and low fPMOXA values. A combination of very low molecular mass PDMS and small fPMOXA values induced formation of worm-like micelles, while low molecular mass PDMS and high fPMOXA values generated a mixture of small micelles and spherical particles. The polymersome membranes were characterized by electron paramagnetic resonance, which indicated a multilayer structure (PMOXA outer layer, PDMS middle part, and PMOXA inner layer) with low flexibility and permeability. Addition of detergent increased both the flexibility and permeability of the PDMS block, which was proven to act as a barrier layer for the membranes.

Formation of worm-like micelles in mixed N-hexadecyl-N-methylpyrrolidinium bromide-based cationic surfactant and anionic surfactant systems.

Through the descriptive and rheological characterization of worm-like micelles formed by N-hexadecyl-N-methylpyrrolidinium bromide and sodium laurate, the formation and properties of the worm-like micelles were affected by the concentrations of sodium laurate and temperature. Additionally, cryogenic transmission electron microscopy images further validated the formation of worm-like micelles.

Effect of presence of benzene ring in surfactant hydrophobic chain on the transformation towards one dimensional aggregate

The formation of wormlike micelle and the following significant changes in rheological properties suffer misunderstanding from both theoretical and fundamental aspects. Recently, we have introduced a theory for interpreting such important phenomenon which is referred to as critical intermolecular forces (CIF). The theory has stated that the hydrophobic effect is the main factor for the formation of worm-like aggregates. Therefore, it seems interesting to check out the validity of this new physical insight through investigating the presence of benzene ring as less hydrophobic group in contrast to that of alkyl in surfactant tail. The mixture of anionic sodium dodecylbenzenesulphonate (SDBS) and cationic cetyltrimethylammonium bromide (CTAB) shows a high dynamic viscosity peak at the ratio of 80/20 of 3wt.% CTAB/SDBS indicating the formation of wormlike micelles. The thermodynamic properties have been evaluated for this mixture exhibiting good agreement with the rheological changes. Interestingly, the results show the presence of benzene ring (in SDBS) causing a negative effect towards the formation of one dimensional aggregate in contrast to previous results which support the proposed CIF theory. The presence of nonionic surfactant TritonX-100 in binary and ternary systems of SDBS and CTAB prohibits the formation of wormlike micelles.

In‐Situ Formation of Viscoelastic Wormlike Micelles in Mixtures of Non‐Surface‐Active Compounds

AbstractViscoelastic fluids based on surfactant self‐assembled wormlike micelles have been in focus over the past decade. In this work, we report wormlike micellar solutions formed in situ by simply mixing two non‐surface‐active compounds, N‐(3‐(dimethylamino)propyl)palmitamide (C16AMPM) and salicylic acid (HSal), without specialized organic synthesis of a surfactant. In the absence of HSal, C16AMPM is poorly soluble in pure water; after introducing HSal, C16AMPM is protonated into quaternary ammonium, behaving like a cationic surfactant with a low critical micellar concentration (0.25 mM) and a small area per molecule, which favors the formation of long cylindrical wormlike micelles. Above the overlapping concentration (~28 mM), the wormlike micelles formed entangle each other into viscoelastic networks, enhancing the viscosity by several orders of magnitude. In contrast to the worms formed by a single ultra‐long‐chain surfactant, the current system shows the advantages of a smaller flow activation energy and end‐cap energy, simpler formulation and lower cost, which make it more suitable for practical use.

The Elasticity of Soap Bubbles Containing Wormlike Micelles

Slow-motion imaging of the rupture of soap bubbles generally shows the edges of liquid films retracting at a constant speed (known as the Taylor-Culick velocity). Here we investigate soap bubbles formed from simple solutions of a cationic surfactant (cetyltrimethylammonium bromide - CTAB) and sodium salicylate. The interaction of salicylate ions with CTAB leads to the formation of wormlike micelles (WLM), which yield a viscoelastic behavior to the liquid film of the bubble. We demonstrate that these elastic bubbles collapse at a velocity up to 30 times higher than the Taylor-Culick limit, which has never been surpassed. This is because during the bubble inflation, the entangled WLM chains stretch, storing elastic energy. This extra energy is then released during the rupture of the bubble, yielding an additional driving force for film retraction (besides surface tension). This new mechanism for the bursting of elastic bubbles may have important implications to the breakup of viscoelastic sprays in industrial applications.

Manipulation of the viscosity behavior of wormlike micellar gels by changing the molecular structure of added perfumes

We studied the effect of a trace amount of perfumes and oils on the rheological properties of micellar solutions formed in a water/sodium dodecyl sulfate (SDS)/tri(oxyethylene) dodecyl ether (C12EO3) system which gives a maximum zero-shear viscosity as a function of surfactant mixing fraction due to wormlike micelle formation. By adding high-polarity perfumes and oils (9-decen-1-ol, 1-decanol, l-menthol, geraniol and α-terpineol), the viscosity peak shifts to lower hydrophobic surfactant composition and the degree of the viscosity peak shift is the largest for the linear-chain molecules and smaller for the branched or cyclic molecules. Dynamic frequency tests show that the zero-shear viscosity behavior for different high-polarity perfume and oil systems varies due to the change in the relaxation time behavior. The linear-chain molecules can penetrate well in the palisade layer of micelles and the penetration could be interrupted by branched or cyclic molecular architecture. On the other hand, by adding low-polarity perfumes and oils (p-cymene, hexahydrocumene, butylbenzene, d-limonene and decane), the behavior of the viscosity curve is quite different for decane and for other molecules, i.e. decane decreases the viscosity peak without shift of surfactant mixing fraction whereas other molecules behave as high-polarity molecules.

Effects of Spacer Chain Length of Amino Acid-Based Gemini Surfactants on Wormlike Micelle Formation

We studied the effects of the spacer chain length of amino acid-based gemini surfactants on the formation of wormlike micelles in aqueous solutions. The surfactants used were synthesized by reacting dodecanoylglutamic acid anhydride with diamine compounds (ethylenediamine, pentanediamine, and octanediamine), and were abbreviated as 12-GsG-12 (s: the spacer chain length of 2, 5, and 8 methylene units). These surfactants yielded viscoelastic wormlike micellar solutions at pH 9 upon mixing with a cationic monomeric surfactant, hexadecyltrimethylammonium bromide (HTAB). We found that the rheological behavior was strongly dependent on the spacer chain length and HTAB concentration. When the shortest spacer chain analogue (12-G2G-12) was used, an increased HTAB concentration resulted in the following structural transformations of the micelles: (i) spherical or rodlike micelles; (ii) anionic wormlike micelles exhibiting a transient network structure; (iii) anionic wormlike micelles with a micellar branching or interconnected structure; and (iv) cationic wormlike micelles. Similarly, when the middle spacer chain analogue (12-G5G-12) was used, a structural transformation from anionic to cationic wormlike micelles occurs; however, molecular aggregates with a lower positive curvature were also formed in this transition region. When the longest spacer analogue (12-G8G-12) was used, the formation of cation-rich molecular aggregates was not observed. These transition behaviors were attributed to the packing geometry of the gemini surfactants with HTAB. Additionally, as the spacer chain length increased, the zero-shear viscosity in the anionic wormlike micellar region decreased, suggesting limited one-dimensional micellar growth of spherical, rodlike, or anionic wormlike micelles.

Rheological Behavior of Viscoelastic Wormlike Micelles in CTAB/SSS/H2O Systems

The effect of the addition of sodium 4-styrenesulfonate (SSS) and KNO3 as well as temperature and shear rate on the structural transition of aqueous micellar solutions of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) was studied by viscosity. The effect of hydrocarbons on viscoelastic CTAB solutions was also examined. Possible mechanism for formation of CTAB wormlike micelles in the presence of sodium 4-styrenesulfonate (SSS) and KNO3 was discussed. The rapid increase in the apparent viscosity of CTAB solutions on the addition of SSS and KNO3 was due to the transition in micellar shape from spheres to wormlike ones. The rheological properties of CTAB solutions fit Maxwell model at low shear frequency. AFM image indicated a structure of transient network of CTAB/SSS/KNO3/H2O solution.

Effects of sodium salicylate on the microstructure of a novel zwitterionic gemini surfactant and its rheological responses

Solutions of a novel zwitterionic gemini surfactant, 1,2-bis[N-ethyl-N-(sodium 2-hydroxyl-3-sulfopropyl)-dodecyl-ammonium] ethane betaine (DBA2-12), in presence of sodium salicylate (NaSal) can form wormlike micelles and thereby show a viscoelasticity. At low molar ratio of NaSal/DBA2-12, R ≤ 0.3, the systems behaved like a Newton fluid. However, as the R increased, the systems exhibited shear-thinning behavior. The zero-shear viscosity η 0 increased dramatically with increasing R and peaked with R = 0.8 at a value of 18.8 Pa s. This was attributed to the formation of long wormlike micelles (1.6 ∼ 2.9 μm) and network structure confirmed by scanning electron microscopy. Further increase in R beyond 0.8 resulted in a slight decrease in η 0, which may be caused by the branched micelles formed at high salt concentration. In addition, the tested systems showed a Maxwellian behavior at lower frequencies, but deviated from the Maxwellian mode at higher frequencies.

Unusual viscoelasticity behaviour in aqueous solutions containing a photoresponsive amphiphile

Here, we report unusual behaviour of the viscoelasticity of surfactant aqueous solutions consisting of cationic cetyltrimethylammonium bromide (CTAB) and an anionic photoresponsive amphiphile, sodium [4-(4-butylphenylazo)phenoxy]acetate (C4AzoNa). When C4AzoNa molecules are trans-isomers, spheroidal micelles are formed in the surfactant solution, the viscosity of which is low. Irradiation of this solution by ultraviolet (UV) light yields an aqueous solution of CTAB/cis-C4AzoNa (cis-isomers of C4AzoNa), which is a highly viscous gel consisting of wormlike micelles. The drastic change in the surfactant solution viscosity is attributed to the formation and disruption of wormlike micelles. The geometrical structural transformation of the azobenzene groups in the C4AzoNa molecules of the CTAB/C4AzoNa mixture would lead to a change in the critical packing parameter of the mixture, thereby inducing the morphological transformation of the aggregates (spheroidal micelles to wormlike micelles). To our knowledge, this is the first report of a drastic increase in surfactant solution viscosity by UV light irradiation.

Efficient Control of the Rheological and Surface Properties of Surfactant Solutions Containing C8–C18 Fatty Acids as Cosurfactants

Systematic experimental study is performed about the effects of chain length (varied between C8 and C18) and concentration of fatty acids (FAc), used as cosurfactants to the mixture of the anionic surfactant SLES and the zwitterionic surfactant CAPB. The following properties are studied: bulk viscosity of the concentrated solutions (10 wt % surfactants), dynamic and equilibrium surface tensions, surface modulus, and foam rheological properties for the diluted foaming solutions (0.5 wt % surfactants). The obtained results show that C8-C10 FAc induce formation of wormlike micelles in the concentrated surfactant solutions, which leads to transformation of these solutions into viscoelastic fluids with very high apparent viscosity. The same FAc shorten the characteristic adsorption time of the diluted solutions by more than 10 times. In contrast, C14-C18 FAc have small effect on the viscosity of the concentrated solutions but increase the surface modulus above 350 mN/m, which leads to higher friction inside sheared foams and to much smaller bubbles in the formed foams. The intermediate chain C12 FAc combines some of the properties seen with C10 FAc and other properties seen with C14 FAc. These results clearly demonstrate how appropriate cosurfactants can be used for efficient control of the rheological properties of concentrated surfactant solutions and of some important foam attributes, such as bubble size and foam rheology.

Effect of a Hydrophilic Head Group on Krafft Temperature, Surface Activities and Rheological Behaviors of Erucyl Amidobetaines

AbstractUltra‐long‐chain amidobetaine surfactants have become one of the hot topics recently, but the influence of the hydrophilic head group on the aggregation behaviors and the correlation between surface activities and thickening ability have been less documented. In this work, comparative studies on the effect of the hydrophilic group on Krafft temperature (TK), surface activities and rheological behaviors of erucyl amidobetaines with sulfonate, hydroxyl‐sulfonate or carboxylate were examined. Compared to the sulfobetaines, the carboxybetaine is more water‐soluble; the addition of an hydroxyl group onto the head group of sulfobetaine increases water‐solubility leading to a lower TK. Unexpectedly, the nature of the head groups has little effect on the critical micelle concentration and thickening ability of these surfactants. The packing parameter prediction verifies the formation of wormlike micelles which accounts for the strong thickening ability of the surfactant aqueous solutions.

A new reverse worm-like micellar system from a lecithin, multivalent carboxylic acid and oil mixture

We developed new lecithin organogels composed of reverse worm-like micelles with lecithin/multivalent carboxylic acid/oil systems, and discussed their phase behavior and rheological properties. The most important findings in this study are the following. From a screening test of many carboxylic acids for gelation, it was found that the number and position of the carboxyl groups of the multivalent carboxylic acids are the determinants for the formation of reverse worm-like micelles, and appropriate carboxylic acids such as citric acid and 1,2,3-propanetricarboxylic acid can change the lecithin/oil solution into a gel. Furthermore, upon addition of these carboxylic acids, the zero-shear viscosity of solutions increased monotonically until phase separation or cloudiness occurred. For example, when citric acid was used, the maximum zero-shear viscosity of the solution was 70,000,000 times larger than that of n-decane. From studies on the scaling of rheological parameters, it was found that further addition of multivalent carboxylic acids not only induced the formation of linear reverse worm-like micelles but also brought about their branching.

Self-assembled nano structures of cationic ester-containing gemini surfactants: The surfactant structure and salt effects

The aggregation behavior of ester-containing cationic gemini surfactants, dodecyl esterquat and dodecyl betainate geminis was investigated using tensiometry, conductometry, viscometry, dynamic light scattering (DLS), transmission electron microscopy (TEM) and optical microscopy techniques in the absence and presence of NaBr electrolyte. The effect of chemical structure (i.e. the presence of ester bond in alkyl chain and the spacer length) on physicochemical properties and morphology of the surfactants was studied. The results showed that the ester-containing gemini surfactants formed spherical aggregates at dilute concentration (1.1%wt). At higher concentration (∼3.7%wt) the morphology is different depending on the position of ester bond in alkyl chain and the spacer length. Dodecyl betainate gemini with short spacer (s=2) formed gel as a result of the formation of worm-like micelles in the aqueous solution. Dodecyl betainate gemini (s=3) formed large vesicles enclosing smaller ones and dodecyl esterquat gemini (s=3) formed both short cylindrical and spherical micelles. The salt addition induced the growth of micelles and in the case of dodecyl betainate (s=2) gemini changed the morphology from worm-like micelles to lamellar phase.

Molecular Interactions between Lecithin and Bile Salts/Acids in Oils and Their Effects on Reverse Micellization

It has been known that the addition of bile salts to lecithin organosols induces the formation of reverse wormlike micelles and that the worms are similar to long polymer chains that entangle each other to form viscoelastic solutions. In this study, we further investigated the effects of different bile salts and bile acids on the growth of lecithin reverse worms in cyclohexane and n-decane. We utilized rheological and small-angle scattering techniques to analyze the properties and structures of the reverse micelles. All of the bile salts can transform the originally spherical lecithin reverse micelles into wormlike micelles and their rheological behaviors can be described by the single-relaxation-time Maxwell model. However, their efficiencies to induce the worms are different. In contrast, before phase separation, bile acids can induce only short cylindrical micelles that are not long enough to impart viscoelasticity. We used Fourier transform infrared spectroscopy to investigate the interactions between lecithin and bile salts/acids and found that different bile salts/acids employ different functional groups to form hydrogen bonds with lecithin. Such effects determine the relative positions of the bile salts/acids in the headgroups of lecithin, thus resulting in varying efficiencies to alter the effective critical packing parameter for the formation of wormlike micelles. This work highlights the importance of intermolecular interactions in molecular self-assembly.

Multiscale study on the interaction mechanism between ginsenoside biosurfactant and saikosaponin a

Ginsenoside is an important class of saponin biosurfactant that is derived from ginseng. The interactions between ginsenoside Ro, Rb1, and Rg1 with saikosaponin a (SSa) were explored using multiscale methods. The order of interaction strength was found to be Ro>Rb1>Rg1. Ro markedly increased the solubility of SSa; however, Rb1 could only disperse SSa solid in aqueous medium. No significant interaction was observed between Rg1 and SSa. Ro formed vesicles in aqueous medium while Rb1 and Rg1 formed spherical micelles. The differences in the available surface area of the aggregates appear to have some influence on the interactions between ginsenoside and SSa. However, more important effects are related to their chemical structures and interaction energy. According to the molecular simulation results, glucuronic acid linked to Ro molecules significantly reduced the potential energy through its strong electrical attraction to SSa, which contributed greatly to the strong compatibility between them. The greater number of sugars in Rb1, as compared to Rg1, created more binding sites with SSa, thus resulting in stronger interaction between Rb1 with SSa than between Rg1 and SSa. Spherical and worm-like micelles were found to be formed by Rb1 and SSa molecules. This was different from Ro and SSa, which formed vesicles. The formation of worm-like micelles was through the fusion and modification of small spherical micelles. These results may guide in expanding the applications of ginsenoside.

Structure formation in binary mixtures of lipids and detergents: Self-assembly and vesicle division

Self-assembly dynamics in binary surfactant mixtures and structure changes of lipid vesicles induced by detergent solution are studied using coarse-grained molecular simulations. Disk-shaped micelles, the bicelles, are stabilized by detergents surrounding the rim of a bilayer disk of lipids. The self-assembled bicelles are considerably smaller than bicelles formed from vesicle rupture, and their size is determined by the concentrations of lipids and detergents and the interactions between the two species. The detergent-adsorption induces spontaneous curvature of the vesicle bilayer and results in vesicle division into two vesicles or vesicle rupture into worm-like micelles. The division occurs mainly via the inverse pathway of the modified stalk model. For large spontaneous curvature of the monolayers of the detergents, a pore is often opened, thereby leading to vesicle division or worm-like micelle formation.

Synergistic Interaction of Short-Chain Phospholipids in the Adsorbed Film and Micelles: Study by Surface Tension and Dilational Viscoelasticity Measurements

The aggregate formation and surface adsorption of aqueous binary mixture of short-chain phospholipids, dihexanoyl-phosphatidylcholine (DC6PC), and dioctanoyl-phosphatidylcholine (DC8PC), were examined by surface tension and dilational viscoelasticity measurements. The concentration versus composition diagram of aggregate formation was constructed by analyzing the surface tension data. The diagram demonstrated a synergetic effect that even when the mole fraction of DC8PC in the aqueous solution was 0.02, worm-like micelle was formed and furthermore the addition of DC6PC to DC8PC solution lowered the DC8PC concentration at which worm-like micelle formation starts, although DC6PC molecules do not form worm-like micelles solely. The phase diagram of adsorption was also constructed to elucidate the miscibility of two components in the adsorbed film. The calculated excess Gibbs energy of adsorption was negative, again suggesting a synergistic attractive intermolecular interaction between two species in the adsorbed film. A staggered arrangement was proposed as a favorable intermolecular arrangement. The dilational viscoelasticity was also measured by the electrocapillary wave method, and both storage and loss modulus showed a maximum at around the surface composition of the minimum of the excess Gibbs energy of adsorption.

Formation and properties of wormlike micelles in solutions of a cationic surfactant with a 2-hydroxypropoxy insertion group

The rheological properties of aqueous solutions of a cationic surfactant, 3-hexadecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R16HTAB), and its mixed solution system with sodium salicylate (NaSal) have been studied by using steady state and frequency sweep rheological measurements. The microstructure of the formed wormlike micelles has been ascertained by transmission electronic microscopy and 1H NMR technology. The effects of the surfactant concentration, added salt, temperature and different counterions on the viscoelastic solutions have been systematically investigated. In a salt-free state, the η0 and R16HTAB concentrations obey the relationship of the power law, i.e. η0 ∝ C2.53, in the examined concentration range. The addition of NaSal greatly promoted the micellar growth in R16HTAB aqueous solution and resulted in the generation of wormlike micelles. The causes of the formation of wormlike micelles and the strong network structure have been analyzed.