Shear-induced State Research Articles

Suppression of the Rayleigh–Plateau instability on a vertical fibre coated with wormlike micelle solutions

We report on the Rayleigh-Plateau instability in films of giant micelles solutions coating a vertical fibre. We observe that the dynamics of thin films coating the fibre could be very different from the Newtonian or standard Non-Newtonian cases. By varying the concentration of the components of the solutions and depending on the film thickness, we show for the first time that the Rayleigh-Plateau instability can be stabilized using surfactant solutions. Using global rheology and optical visualisations, we show that the development of shear-induced structures is required to stabilize the micellar film along the fibre. Assuming that the viscoelastic properties of the shear-induced state can be described by a simple model, we suggest that, in addition to the presence of shear-induced structures, the latter must have an elastic modulus greater than a critical value evaluated from a linear stability analysis. Finally, our analysis provides a way of estimating the bulk elasticity of the shear-induced state.

界面活性剤ミセル水溶液中での連続沈降球の速度変化(<小特集>非ニュートン性,機能性を示す複雑流体の流動と応用)

In the present study, motions of a solid sphere falling through aqueous solutions of CTAB/NaSal are examined. At relatively low NaSal: CTAB mole ratios, almost the same increase ratio of the terminal settling velocity with the number of successive sphere drops is observed, independent of the diameter and the density of the sphere. The increase ratio of terminal settling velocity decreases exponentially with increasing interval time of sphere drops. At relatively high NaSal: CTAB mole ratios, the increase in the terminal settling velocity is not observed. The oscillatory change of settling velocity is observed above a critical shear rate of the sphere, accompanied by the vanishing of white turbid streak corresponding to the collapse of the shear-induced state (SIS) in the wake. The change in the settling velocity is explained by the viscous drag force and the additional drag force originated in the formation of the SIS.

Viscosity measurements of ethylene glycol solution with flow drag reduction additives

AbstractThe viscous characteristics of ethylene glycol (EG) solution with flow drag reduction additive have been investigated experimentally. In this study, oleyldihydoroxyetyl amineoxide (ODEAO) was used as the flow drag reduction additive, and an aqueous solution of EG was used as a secondary refrigerant. The viscosity of the EG solution with ODEAO was measured with a rotational rheometer. The experimental parameters of viscosity measurement were the temperature of the EG solution with ODEAO, the ODEAO concentration, and the EG concentration. From the experimental results, the apparent viscosity of the EG solution with ODEAO showed SIS (shear induced state). The non‐linear dependence of shear stress on shear rate has been well approximated by the power‐law model under high shear conditions. The power‐law contents, pseudoplastic viscosity, and index number have been estimated for each experimental parameter. Using the measured viscosity and non‐dimensional analysis, the flow drag and heat transfer reduction effect of the EG solution with ODEAO has been investigated. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(8): 553–567, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20134

2325 円管を流れる界面活性剤水溶液のレイノルズせん断応力(S42-5 複雑流体の流動現象(5),S42 複雑流体の流動現象)

Reynolds shear stress of surfactant solution flowing in a circular pipe was investigated experimentally by means of Laser Doppler anemometery. Concentrations of surfactant solution were 0, 28, 50, 100 ppm, and Reynolds numbers based on a bulk velocity, viscosity of water and a pipe diameter were set to 20000, 40000, 60000. Results show that the extreme suppression of Reynolds shear stress compared to water was occurred in the case of surfactant solution, and this was achieved by counteractions between outward interaction and ejection, inward interaction and sweep, respectively. The shear viscosity calculated from mean velocity distribution and previous results of rheometer test shows that there is a low viscosity region below the region which is in a shear induced state. This region makes a difference in streamwise velocity fluctuation between the cases of upward and downward fluid motion.

213 差分格子ボルツマン法による界面活性剤の SIS に関する研究

Drag reduction caused by surfactant solutions is considered. Surfactant contains threadlike micelles. At a critical shear rate the shear viscosity suddenly increases in this so-called shear-induced state (SIS). At high shear rates the increased shear viscosity gradually decreases. In this paper, two-dimensional numerical simulation in the surfactant solution containing threadlike micelles by the finite difference lattice Boltzmann method is reported. As a result, we formed SIS and checked the shear viscosity increasing at a critical shear rate and the increased shear viscosity decreasing at high shear rates.

Elastic properties of a dilute surfactant solution in the shear induced state

The first normal stress differences N 1 of a highly dilute cationic surfactant solution are investigated in a cone-and-plate rheometer. In continuation of a previous paper (Nowak 1998), where the buildup of a shear induced structure in such a solution was attained after a reduced deformation, the N 1 turned out to be in proportion to the square of the shear rate γ˙ reduced by a critical value γ˙ c in a first range above γ˙ c . At higher shear rates the N 1 tend to lower values than predicted by this relation. Relaxation experiments were performed in the same geometry to determine the characteristic time scales of the shear induced state's decay. In the lower range above &γdot; c the stress decay is a monoexponential process, while a second time constant has to be introduced to describe the relaxation in that range, where the N 1 deviate from the parabolic dependence of the reduced shear rate.

Viscous and elastic properties of a cationic and a zwitterionic drag reducing surfactant

The cationic CTAC and zwitterionic SPE 98330 surfactants were investigated and their rheological properties compared. Also the influence of solvent quality (the presence of ions, particularly Ca 2+) on both the viscosity and elasticity of surfactants were investigated. Differences in the storage modulus, G′, are negligible but there are substantial differences in the loss modulus, G′′. Shear induced state (SIS) was detected in all samples.

Influence of Shear on the Alignment of a Lamellae-Forming Pentablock Copolymer

We characterize shear-induced states of order and disorder in a symmetric lamellae forming poly(cyclohexylethylene) (C)−polyethylene (E) CECEC pentablock copolymer. When subjected to a large amplitude reciprocating shear strain (γ = ±600%) in the ordered lamellae state, the sample rapidly aligns in a perpendicular orientation with long-range order. The order−disorder transition temperature TODT(γ̇) decreases with increasing shear rate γ̇, such that a shear rate of γ̇ = 7 ± 1 s-1 is sufficient to disorder the material nearly 30 °C below the quiescent TODT. Small-angle neutron scattering (SANS) from the sheared disordered state displays a symmetry that suggests a fundamentally different influence of shear compared to earlier observations of shear-induced anisotropy in the disordered states of lamellae forming diblock and triblock copolymers. Abrupt cessation of shear leads to spontaneous lamellar ordering into a macroscopically well-aligned transverse orientation—an arrangement that previously has been inaccessible via processing. In contrast to this behavior, the perpendicular alignment forms when cooling the sample from above the TODT while applying low shear rates, similar to the response of di- and triblock copolymers. These findings shed fresh insight into the complex phenomena that govern flow- and deformation-induced alignment of block copolymer melts.

Heat Transfer Enhancement to the Drag-Reducing Flow of Surfactant Solution in Two-Dimensional Channel With Mesh-Screen Inserts at the Inlet

The heat transfer enhancement of drag-reducing flow of high Reynolds number in a two-dimensional channel by utilizing the characteristic of fluid was studied. As the networks of rod-like micelles in surfactant solution are responsible for suppressing the turbulence in drag-reducing flow, destruction of the structure of networks was considered to eliminate the drag reduction and prevent heat transfer deterioration. By inserting wire mesh in the channel against the flow, the drag-reducing function of the micellar structure in surfactant aqueous solution was successfully switched off. With the Reynolds number close to the first critical Reynolds number, the heat transfer coefficient in the region downstream of the mesh can be improved significantly, reaching the same level as that of water. The region with turbulent heat transfer downstream of the mesh becomes smaller as the concentration of surfactant in the solution increases. Three types of mesh of different wire diameter and opening space were evaluated for their effect in promoting heat transfer and the corresponding pressure loss due to blockage of the mesh. The turbulent intensities were measured downstream from the mesh by using a Laser Doppler Velocimetry (LDV) system. The results indicated that the success of heat transfer enhancement is due to the strong turbulence promoted by the mesh which destroys the network of rod-like micelles by applying high shear stress and thus relaxing the shear induced state (SIS).

Shear-Induced States of Orientation of the Lamellar Phase of C12E4/Water

The shear-induced states of orientation of the lamellar lyotropic mesophase of tetraethylene glycol monododecyl ether (C12E4) in water are investigated by polarizing microscopy, viscometry, small-angle light scattering, and deuteron NMR spectroscopy. The solution containing 40 w/w % surfactant shows a continuous transition from a state of aligned layers, whose normal is parallel to the velocity gradient, to a close packing of multilamellar vesicles (onion state). The size of the vesicles (diameter d) is controlled by the shear rate γ̇, following the relationship d ∝ γ̇a with a ≈ −0.5.

The velocity field of dilute cationic surfactant solutions in a Couette-viscometer

With the aid of particle image velocimetry (PIV) momentary two-dimensional velocity fields of dilute cationic surfactant solutions are measured in an annular gap between coaxial cylinders. In the shear-induced state the velocity profiles of the surfactant solutions differ from a Couette profile drastically: Time dependent flows with high shear rates near the walls are observed. The flow is almost one-dimensional, velocity components in radial or axial direction cannot be detected. The velocity profile can exhibit a local maximum. A macroscopic heterogeneous structure is observed, domains with high viscosity alternate with low viscosity regions. Elastic phenomena are observed in a relaxation experiment. Existing rheometric data of cationic surfactant solutions in the shear-induced state give only apparent viscosities.

Formation of the shear-induced state in dilute cationic surfactant solutions

Formation of the shear-induced state in dilute cationic surfactant solutions

Formation of the shear-induced state in dilute cationic surfactant solutions

In cationic surfactant solutions a change of state occurs due to mechanical stresses. In the dilute regime of rodlike micelles the formation of a so-called Shear-Induced State (SIS) occurs above a critical shear rate. In this context ‘dilute’ means that there is no sterical interaction between rodlike micelles, the solution is below the overlap concentration. Employing a mathematical model, it is shown that aggregation forces are weak compared to hydrodynamic forces. The mathematical formulation is based on a model of Israelachvili which describes the chemical potential of micelles. Hydrodynamic forces are calculated with a rigid-dumbbell model. SIS formation can be explained by the destruction of rodlike micelles.

Shear Thickening of an Aqueous Micellar Solution of Cetyltrimethylammonium Bromide and Sodium Tosylate

In this experimental study we give results concerning the shear thickening behavior exhibited by an aqueous cationic surfactant solution of CTAB in the presence of added NaTOS. We carefully investigate the rheological characteristics of this phenomenon corresponding to a shear induced state (SIS), the reproductibility and also the transient regimes. We show that with steady experiments there exist no hysteresis effect. Finally we give the evolution of the shear thickening characteristics against temperature.

Lamellar lyomesophases under shear as studied by deuterium nuclear magnetic resonance

The lamellar phases of two aqueous ethylene oxide surfactants, tetra(ethylene oxide) dodecyl ether and hexa(ethylene oxide) dodecyl ether, have been investigated by deuterium nuclear magnetic resonance spectroscopy during shear. The evolution of the shear-induced NMR line shapes and their dependence on surfactant concentration, shear geometry and shear history is analyzed. Two of three previously described shear-induced states (Diat O, Roux D, Nallet F (1993) J Phys II France 3: 1427–1452), namely the state of aligned lamellae with the layer normal parallel to the velocity gradient, which occurs at low shear rates, and the vesicular state at intermediate shear rates are found and identified by their characteristics NMR line shapes.

The influence of pre-shearing on the elongational behaviour of dilute polymer and surfactant solutions

Experimental results are presented which provide information about the elongational behaviour of pre-sheared dilute polymer and surfactant solutions. The viscosity behaviour of these pre-sheared solutions is explained on the basis of molecular data and by flow visualization. A rotational viscometer was modified in such a way that the sheared test fluid left the gap of the viscometer through an orifice in the outer cylinder. The flow-rate at a constant pressure drop through the orifice is related to the elongational viscosity of the fluid. The elongational viscosity of dilute polymer solutions increases when a critical shear gradient is exceeded. The critical shear gradient was found to be independent of the polymer concentration. It could be lowered by increasing the molecular weight of the polymer. Visualization of the orifice flows were done in a rectangular channel. A sudden increase of the apparent elongational viscosity, which is found for poly(isobutene) solutions when a certain Deborah number is exceeded, and an increase of the elongational viscosity, which for poly(acrylamide) solutions is independent of the pre-shearing deformation, can both be related to entrance vortices and instabilities of the entrance flow in the orifice. This was confirmed by flow visualization. The surfactant solutions which were used exhibit a sudden increase of the shear viscosity due to the formation of a shear-induced state (SIS) when a critical shear rate is exceeded. In the SIS their elongational viscosity is also increased. However, the Trouton ratio remains at a value of three which is characteristic for Newtonian fluids.

The behaviour of drag-reducing cationic surfactant solutions

The behaviour of two types of drag reducing surfactant solutions was studied in turbulent flows in pipes of different diameters. Our surfactant systems contained rod-like micelles; they consisted of equimolar mixtures ofn-tetradecyltrimethylammonium bromide,n-hexadecyltrimethylammonium bromide, and sodium salicylate. The structure of the turbulence was studied using a laser-Doppler anemometer in a 50 mm pipe. In the turbulent flow regime both surfactant solutions exhibited characteristic flow regimes. These flow regimes can be influenced by changing the amount of excess salt, the surfactant concentration, or the temperature. Shear viscosity measurements in laminar pipe and Couette flows show the occurrence of the so-called shear-induced state, where the viscosity increases and the surfactant solution becomes viscoelastic. The shape of the turbulent velocity profile depends on the flow regime. In the turbulent flow regime at low Reynolds numbers, velocity profiles similar to those observed for dilute polymer solutions are found, whereas at maximum drag reduction conditions more “S-shaped” profiles that show deviations from a logarithmic profile occur. An attempt is made to explain the drag reduction by rod-like micelles by combining the results of the rheological and the turbulence structure measurements.

Flow birefringence and rheological measurements on shear induced micellar structures

Aqueous solutions of cationic surfactant systems with strongly binding counterions show the striking phenomenon of shear induced phase transitions. At low shear rates or angular frequencies, the solutions exhibit Newtonian flow. At high rates of shear, however, the rheological properties change dramatically. Above a well defined threshold value of the velocity gradient, a supermolecular structure can be formed from micellar aggregates. This shear induced structure (SIS) behaves like a gel and exhibits strong flow birefringence. The formation of the shear induced structure is very complicated and depends on the specific conditions of the surfactant system. In this paper we discuss new results which have been obtained from rheological measurements and from flow birefringence data. We examine the stability of the shear induced state as a function of temperature, surfactant concentration and salt concentration and we analyse the effect of solubilisation of alcohols and hydrocarbons. The results are interpreted in terms of a kinetic model which accounts for the observed behavior.