Viscoelastic wormlike micelles and their applications

Yang, Jiang

doi:10.1016/s1359-0294(02)00071-7

Cited by 565 publications

(386 citation statements)

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“…The values of the critical micelle concentration (CMC) are about 0.24 wt% (SLS) and 0.11 wt% (ESLS) [7,[44][45][46][47][48][49][50]. These results are unexpected as the hydrophilic part in the ESLS molecule is expanded by addition of two molecules of ethylene oxide which should increase water solubility and ''shift'' the CMC value towards higher concentrations.…”

Section: Micellar Solutions Of Alkyl Sulfatesmentioning

confidence: 98%

The Effect of Concentration on Lubricating Properties of Aqueous Solutions of Sodium Lauryl Sulfate and Ethoxylated Sodium Lauryl Sulfate

2010

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The objective of this study was to formulate new ecological lubricating substances, primarily water-based, and to verify their tribological and physicochemical properties. Initially, simple binary solutions were investigated. Then, various additives were added depending on application targets. Two alkyl sulfates were selected as additives modifying lubricating properties of water: sodium lauryl sulfate (SLS) and ethoxylated sodium lauryl sulfate (ESLS). They have an identical hydrophobic part in the form of an alkyl chain consisting of 12 carbon atoms. The SO 4 2-anion forms the hydrophilic part in SLS molecules, whereas an ESLS molecule also contains two mers of ethylene oxide which cause an increase in its hydrophilicity relative to SLS. Both SLS and ESLS exhibit high surface activity measured by their surface tension. Micelles form in aqueous solutions of alkyl sulfates at low concentrations of the order of 1%, whereas the presence of liquid crystalline phases can be found at the concentrations of 40 and 70%. High surface activity and formation of structures in the solutions (micelles, mesophases) formed the basis for application of the compounds as additives modifying lubricating properties. Tribological properties of aqueous solutions of alkyl sulfates were verified with a four-ball machine (T02 tester) at a constant load of 2 kN. The values of friction coefficient (l) were a measure of motion resistance, while the wear scar diameter (d) was a measure of wear. Alkyl sulfates significantly improve tribological properties of water. The coefficient of friction decreased sixfold and the wear scar diameter decreased by as much as twofold relative to the base. Non-monotonic changes in the tribological properties measured were observed as a function of concentration of additives. An attempt was made to relate those atypical changes with the presence of micelles and mesophases in both the surface phase and the bulk phase. In the model proposed the whole concentration range was divided into four areas in which tribological properties correspond well with physicochemical properties, particularly with the structures formed in solutions and at the interface.

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Section: Micellar Solutions Of Alkyl Sulfatesmentioning

confidence: 98%

The Effect of Concentration on Lubricating Properties of Aqueous Solutions of Sodium Lauryl Sulfate and Ethoxylated Sodium Lauryl Sulfate

2010

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“…À ]. 44,45 The inorganic counterions of NO 3 À and NH 2 NH 3 + bind moderately to cationic CTAB and anionic SDS micelles by electrostatic attraction and screen the repulsions between the charged headgroups, respectively. Thus, the area per headgroup of the surfactant molecule is decreased, resulting in an increase of the critical packing parameter p, 39 which is beneficial to the formation of larger assemblies such as wormlike micelles.…”

Section: Freeze-fracture Transmission Electron Microscopy (Ff-tem)mentioning

confidence: 99%

“…It is believed that the present study is the first example that inorganic salt induces micellar growth and viscoelastic behavior significantly in both cationic and anionic surfactant solutions. The inorganic salt discussed here is an ionic compound, hydrazine nitrate (HN), which is composed of positively charged [NH 2 NH 3 + ] and negatively charged [NO 3 À ]. We focus on the viscoelastic behavior of cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic surfactant ABSTRACT: Hydrazine nitrate (HN), an inorganic salt, was first found to have dual effects on inducing obvious viscoelasticity of both cationic and anionic surfactant solutions.…”

mentioning

confidence: 99%

A Dually Effective Inorganic Salt at Inducing Obvious Viscoelastic Behavior of both Cationic and Anionic Surfactant Solutions

Xia

Wang

et al. 2011

Langmuir

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Viscoelasticity, induced by the entanglement of wormlike or threadlike micelles, has been observed in various surfactant systems and drawn considerable interest in both fundamental and applied science owing to the systems' special rheological properties. 1À6 The rheology of these viscoelastic surfactant fluids is similar to that of the solutions of flexible polymers. 7 However, unlike covalent chemical bonding polymers, self-assembled wormlike micelles are in dynamic equilibrium with their monomers, which are called "living polymers" owing to their ability to break and recombine rapidly. 8,9 The viscoelastic wormlike micelles often show relaxation behavior that can be described by a Maxwell model with a single relaxation time, a living polymer model proposed by Cates et al. 9À11 Viscoelastic wormlike micelles formed by ionic surfactants, especially cationic surfactants, upon addition of various additives have been studied extensively. 12À18 The additives are either simple inorganic salts or structure-forming benzyl hydrotropes, with the molar ratio of salt to surfactant typically above 1 for the former while much lower for the latter. The most interesting features of wormlike micellar solutions are their fascinating microstructural evolution and their linear and nonlinear viscoelastic behavior, depending on the interaction between the surfactant and additive molecules. Inorganic counterions (e.g., F À , Cl À , Br À , NO 3 À ) bind moderately to cationic micelles and thus lead to gradual micellar growth by screening the repulsion between the charged headgroups, 19À22 but for the same charged surfactants, i.e., anionic surfactants, the inorganic salts only play a role in regulating the ionic strength of the solutions. 23 Moreover, at high concentrations of surfactant and salt, phase separation often occurs due to the formation of precipitate, which is generally called the salting-out effect. 24À26 Compared with inorganic salts, organic counterions or hydrotropic salts that strongly bind to the micellar surface are highly efficient in promoting micellar growth 16,22,27 and inducing wormlike micelles at a significantly low ratio of salt to surfactant. However, similar to inorganic salts, only the oppositely charged hydrotropic salts can induce such microstructure transition and viscoelastic behavior in surfactant systems. On the whole, these additives induce complicated viscoelastic responses which are strongly dependent on the electric properties of the additives, and only the oppositely charged additives can show strong interaction with the surfactants, regardless of whether they are inorganic salts or hydrotropic salts.Although simple additive effects for ionic surfactants have been studied extensively, there are few reports of the abovementioned effects induced only by one salt for both cationic and anionic surfactants. It is believed that the present study is the first example that inorganic salt induces micellar growth and viscoelastic behavior significantly in both cationic and anionic surfactant soluti...

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“…4, 24 and references therein), and flow-induced structure formation (3,(12)(13)(14)(25)(26)(27)(28)(29)(30)(31)(32). Wormlike micelles have also found applications in oil recovery, drag reduction, nanotemplating, and many biomedical and health care products (33)(34)(35). Despite widespread use in different fields, the microscopic structures and mechanisms by which wormlike micelles form under flow are not fully understood, and thus remain an active area of research.…”

mentioning

confidence: 99%

Microstructure and rheology of a flow-induced structured phase in wormlike micellar solutions

Cardiel

Dohnálková

Dubash

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Surfactant molecules can self-assemble into various morphologies under proper combinations of ionic strength, temperature, and flow conditions. At equilibrium, wormlike micelles can transition from entangled to branched and multiconnected structures with increasing salt concentration. Under certain flow conditions, micellar structural transitions follow different trajectories. In this work, we consider the flow of two semidilute wormlike micellar solutions through microposts, focusing on their microstructural and rheological evolutions. Both solutions contain cetyltrimethylammonium bromide and sodium salicylate. One is weakly viscoelastic and shear thickening, whereas the other is strongly viscoelastic and shear thinning. When subjected to strain rates of ∼10 3 s −1 and strains of ∼10 3 , we observe the formation of a stable flow-induced structured phase (FISP), with entangled, branched, and multiconnected micellar bundles, as evidenced by electron microscopy. The high stretching and flow alignment in the microposts enhance the flexibility and lower the bending modulus of the wormlike micelles. As flexible micelles flow through the microposts, it becomes energetically favorable to minimize the number of end caps while concurrently promoting the formation of cross-links. The presence of spatial confinement and extensional flow also enhances entropic fluctuations, lowering the energy barrier between states, thus increasing transition frequencies between states and enabling FISP formation. Whereas the rheological properties (zero-shear viscosity, plateau modulus, and stress relaxation time) of the shear-thickening precursor are smaller than those of the FISP, those of the shear-thinning precursor are several times larger than those of the FISP. This rheological property variation stems from differences in the structural evolution from the precursor to the FISP. microfluidics | microrheology | mesh size S urfactant molecules in aqueous solutions can self-assemble into different structures, such as spherical micelles, cylindrical micelles, lamellar phases, and vesicles (1). The morphology of these self-assembled structures is influenced by surfactant concentration, temperature, external additives (e.g., cosurfactants or salts), and flow conditions. Cylindrical micelles in the presence of inorganic or organic salts can self-assemble into large, flexible, and elongated wormlike micelles that exhibit viscoelastic properties (2-4). The ionic strength of the salt screens the electrostatic repulsions between the charged surfactant head groups, promoting cylindrical micellar growth (1-3). At higher salt concentrations, the entangled linear micelles can transition to branched and multiconnected micellar networks, as evidenced by rheological measurements, light scattering techniques, and electron microcopy (EM) imaging (5-18). Additionally, wormlike micellar solutions are known to exhibit a variety of interesting phenomena, some of which are shear banding (19-21), shear thickening (22, 23), shear-induced transitions and insta...

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Viscoelastic wormlike micelles and their applications

Cited by 565 publications

References 37 publications

The Effect of Concentration on Lubricating Properties of Aqueous Solutions of Sodium Lauryl Sulfate and Ethoxylated Sodium Lauryl Sulfate

The Effect of Concentration on Lubricating Properties of Aqueous Solutions of Sodium Lauryl Sulfate and Ethoxylated Sodium Lauryl Sulfate

A Dually Effective Inorganic Salt at Inducing Obvious Viscoelastic Behavior of both Cationic and Anionic Surfactant Solutions

Microstructure and rheology of a flow-induced structured phase in wormlike micellar solutions

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