Dilute Surfactant Solutions Research Articles

Absolute small angle light scattering measurements from weakly scattering systems in a shear flow apparatus

We describe an optical detection layout that allows absolute small angle light scattering measurements on samples sheared in a concentric cylinders geometry. The two main features are the use of a focused incident beam and of a spatial filter that minimize the problem of stray light arising from digs and scratches in the optical path. The scattering intensity is imaged directly onto a cooled 12 bits charge-coupled device sensor. We are thus able to measure scattering intensities as low as about 4×10−4 cm−1 (about ten times the intensity scattered from a toluene standard) for scattering wave vector values between 5×10−5 and 3.5×10−4 Å−1. Some preliminary results of experiments on dilute surfactant solutions are given to demonstrate the performance of the instrument.

Light Sheet Visualization of the Shear-Induced Flow Pattern of Cationic Surfactant Solutions in a Searle Geometry

The flow patterns in a Searle gap of two dilute cationic surfactant solutions, tetradecyl trimethyl ammonium salicylate (TTASal) and hexadecyl trimethyl ammonium salicylate (HTASal), are investigated by means of a light sheet visualization. Although the surfactant solutions differ only slightly in the chain length of the surfactant molecule and in concentration, the observed structures in flow are significantly different. In the case of the TTASal solution the observed structures are dark and only a short temporal evolution takes place, with a final state of inwardly and outwardly developing string-like structures similar for all shear rates above a critical value and with a limited amount of structures for high shear rates. The structures in the HTASal solution are in contrast mainly light and the temporal evolution is quite long, becomes faster with shear rate and shows different states in accordance to the shear rates. For higher shear rates typically first finger-like, afterwards bubble-like structures and finally a kind of homogenization can be observed.

715 界面活性剤水溶液の円柱群内における圧力損失と流れの可視化

715 界面活性剤水溶液の円柱群内における圧力損失と流れの可視化

Cone angle effects, radial pressure profile, and second normal stress difference for shear-thickening wormlike micelles

Many dilute surfactant solutions containing long, thin, wormlike micelles undergo a shear-thickening transition at which the apparent viscosity jumps to a much higher value due to the formation of shear-induced structures. However, the behavior of the normal-stress differences N1 and N2 has not been studied at the low-shear rates and shear stresses (<0.1 Pa) at which shear thickening occurs in most of the commonly studied systems, such as aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSS). For dilute equimolar solutions of CTAB/NaSS, the validity of measurements of the shear flow properties η, N1 and N2 via cone-and-plate rheometry is assessed by systematically varying the cone angle, and by measuring the pressure profile during cone-and-plate flows. The dependence on the cone angle of the apparent viscosity value is consistent with a stratified fluid structure, as shown to occur in Couette rheometers by Hu and co-workers [Hu, Y. T. et al., J. Rheol. 42, 1209–1226 (199...

Measurement of wall-slip-layer rheology in shear-thickening wormy micelle solutions

A microscope-mounted torsional shearing-flow cell is constructed and microscopic particle imaging velocimetry is employed to directly visualize and map the velocity slip layer in a shearing flow of dilute micellar surfactant solutions of cetyltriammonium bromide/sodium salicylate. It is shown that the thickness of the wall-slip layer is about 100 μm at low shear rates, decreasing to around 50–60 μm at high shear rates. Surprisingly, we find that the wall slip layer emerges only near the upper rotating plate of the flow cell, and not the lower surface. The rheological properties of the wormy micellar solutions are also measured by using a stress-controlled rheometer and the results are compared to the visualization results of wall-slip velocity in the shearing-flow cell. The rheometer measurements are consistent with literature reports [Hu et al. (1998a,1998b)] in that there is a critical shear rate at which the apparent shear viscosity increases drastically. Above the critical point, the shear viscosity r...

Comparison of drag reduction, rheology, microstructure and stress-induced precipitation of dilute cationic surfactant solutions with odd and even alkyl chains

Cationic surfactant systems of different alkyl chain lengths with counterion, CnTAC(5 mmol/l)/3-Cl-Benzoate(12.5 mmol/l) (n=15, 16, 17, 18), were investigated for drag reduction, rheological behaviors, microstructure, and stress-induced precipitation. These are the first measurements of these characteristics for odd chain length (C15 and C17) quaternary ammonium surfactants. The lower and upper effective drag reduction temperature limits, viscoelasticity, and stress-induced precipitation temperature increased with alkyl chain length. Krafft temperature, critical turbidity temperature, and lower drag reduction effectiveness temperature limit showed a zigzag odd-even effect, while the stress-induced precipitation temperature did not. Light microscopy and cryo-TEM showed that cooling the C15 solution below 20 °C produced crystals, while above that temperature threadlike micelles were present. The same was true for the solutions of C18 that had threadlike micellar network microstructures when clear and crystals formed upon cooling. Micellar solutions can remain in a homogenous metastable state at a temperature below the Krafft temperature and above the critical turbidity temperature for days without external disturbance. Imposition of flow stress causes the systems to overcome the energy barrier and precipitate.

添加剤を用いた抵抗低減流れのレイノルズ応力に寄与するコヒーレント構造に関する研究

Dilute polymer solutions produce considerable drag reduction in turbulent pipe flows. The mechanisms of drag reduction have been widely studied by many researchers. Despite these many their efforts, it is still difficult to define the mechanisms. In order to understand the turbulent structures of dilute polymer solution flow and surfactant solution flow, we measured 2 components of velocity by 2D-LDV, estimated mean velocity and turbulent intensity, and calculated Reynolds shear stress from the velocity fluctuation data. Reynolds shear stress was analyzed by classifying the data into four quadrants. The characteristics of coherent structure (amplitude for each event, amplitude ratio, probability for each event) are discussed and compared with drag reducing flow and solvent (water) flow. It was found that the contributions to Reynolds shear stress from ejection(event of quadrant 2 ) and sweep(event of quadrant 4 ) are smaller near the wall in drag reducing flow than in solvent flow. We also found that the contributions to Reynolds shear stress from outward interaction(event of quadrant 1 ) and wallward interaction(event of quadrant 3 ) are important to reduce the drag. Contributions from each event in high drag reducing flow such as surfactant flow are equal, thus the flow has no coherent structure and it is a randomly mixing flow. Moreover, the relationships between eddy extension and Reynolds shear stress in drag reducing flows are discussed under the consideration that the drag reducing solutions are viscoelastic fluids. It is predicted that the eddy extension of drag reducing flow would be suppressed by the elasticity of the surfactant. The results obtained from this research are useful for the construction of a constitutive equation.

Phase diagram of dilute lattice surfactant solution

We have studied the temperature–composition phase diagram for a dilute surfactant model solution on the square lattice through Monte Carlo simulations. A micellar region and a solubility line were identified from the measurement of different properties, among which the volume fraction of aggregate, specific heat, and convergence of relaxation from different initial conditions. We have compared properties of the above system with those of a symmetric lattice solution in the dilute regime. Comparison of data allow an interpretation of the micellar phase as a transition region between a microscopically homogeneous phase and a solid phase.

Adsorption of Anionic Surfactant by Activated Carbon: Effect of Surface Chemistry, Ionic Strength, and Hydrophobicity

This work investigates the interrelationship between the adsorbent surface chemistry and relative hydrophobic nature and the solution ionic strength and solution hydrophobicity during dilute anionic surfactant solution adsorption. The adsorbents were coconut- and coal-based, steam-activated carbons and wood-based, acid-activated carbons. The adsorptives were dodecanoic acid and octanoic acid dissolved in water or strong caustic solution. The activated carbons (ACs) were immersed in the strong caustic solution at different temperatures for various lengths of time prior to adsorption measurements. The oxygen content and surface functional group chemistry of each AC sample was analyzed using elemental analysis and X-ray photoelectron spectroscopy. The equilibrium solution concentration of each surfactant was determined using gas chromatography–flame ionization detection techniques. The amount of surfactant adsorbed by each AC indicates that an inverse linear relationship exists between the amount of surfactant adsorbed and the adsorbent oxygen content. Although the steam-activated carbons offer lower pore volumes than the acid-activated carbons, they exhibit the higher adsorption capacity. The high solution chemistry pH promotes adsorbent surface oxidation and anionic surfactant dissociation, leading to an interfacial repulsion force and decreased C12- and C8-acid adsorption. Overall, this study demonstrates that both the surface chemistry and the solution properties should be considered for an adsorption analysis since each has a significant influence on the adsorption process.

Flow regimes of dilute surfactant solutions

The shear-thickening of dilute surfactant solutions is investigated using water/cethyltrimethylammonium tosylate (CTAT) systems. We show that shear induced structures (SIS) are obtained in Couette and parallel-plate flows when the shear stress is higher than a critical shear stress, independently of the type of shear cell. Three different regimes are observed in Couette flow, confirming the results of Hu and co-workers on TTAA/NaSal/water systems. Flow regimes in parallel-plate flow geometries are studied with the aid of particle image velocimetry (PIV). Particular attention is paid to the calibration of the experimental set-up using pure water in order to distinguish between deviations of the rheometric velocity profile due to the onset of purely hydrodynamic instabilities from those due to the occurrence of SIS. It is noteworthy that spatial and temporal fluctuations in the local velocity fields are observed when SIS exists, even when rheometric measurements show an apparently steady-state situation. When no SIS is present we found that the surfactant solutions behave like Newtonian fluids. Laminar secondary flows are present for both cells under the same conditions as those found for classical hydrodynamics.

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.

The flow of a dilute cationic surfactant solution past a circular cylinder

The influence of a dilute solution of the cationic surfactant C14Sal on the flow past a cylinder was investigated by means of LDV and Toepler Schlieren optics for visualization of both the flow and structure of the fluid. At low Reynolds numbers the flow is similar to the Newtonian Karman vortex street. The periodic vortex shedding disappears simultaneously with the occurrence of a shear-induced structure. The alteration of the turbulence characteristics is especially pronounced in the turbulent velocity fluctuations with the urms being many times over the values in water, whereas the vrms are drastically reduced.

A105 界面活性剤水溶液の噴流特性におよぼす温度の影響(オーガナイズドセッション1 : 機能性流体の熱伝達)

The present experiment study is conducted to examine the near field characteristics of the axisymmetric jet discharged from circular pipe for a dilute drag-reducing surfactant solution (Ethoquad O/12). The temperature effect on the jet behavior is studied for a fixed Reynolds number of 10000. It is found that the turbulence suppression effect reduces with the development of jet and strongly depends on the temperature.

Influence of Added Electrolytes on the Lyotropic Phase Behavior of Triethylammoniodecyloxycyanobiphenyl Bromide (OCB-C10NEt3Br)

The influence of added electrolytes (NaBr, NaCl, Na2SO4, Na3PO4, Na2HPO4, NaSCN) on the lyotropic mesophase behavior of triethylammoniodecyloxycyanobipenyl bromide (OCB-C10NEt3) has been studied using optical microscopy, X-ray diffraction, and NMR. Optical microscopy was employed to map the existence regions of the lamellar mesophase, while X-ray diffraction gave its interaggregate dimensions, and NMR was employed to monitor water ordering. Only lamellar and micellar phases have been observed. In all of the electrolytes except NaSCN, partial miscibility of surfactant and water is induced above a certain concentration. This usually involves the separation of a dilute surfactant solution from a more concentrated one. It does not occur within the extensive lamellar phase region. X-ray diffraction and NMR results demonstrate that the major influence of the electrolytes is to reduce the area per headgroup within the aggregates. The effects of the electrolytes follow the Hofmeister series and are attributed to adsorption or desorption of anions at the aggregate surface rather than to changes in “water structure”. Sodium thiocyanate causes the occurrence of a “re-entrant” isotropic phase, in part because the lamellar phase is stabilized to low concentrations. The displacement of OCB groups from the micellar surface by SCN ions is suggested to account for this, which, if valid, offers a potential route to obtaining true amphitropic mesophases (i.e., materials with both thermotropic and lyotropic liquid crystalline order).

Surfactant Tracheobronchial Lavage for the Management of a Rabbit Model of Meconium Aspiration Syndrome

We evaluated the effect of tracheobronchial lavage with diluted surfactant solution (bovine lipid extract surfactant, bLES) in a rabbit model of meconium aspiration. All animals were anaesthetized, tracheotomized and given 3–4 ml/kg of 25% slurry of human meconium into the endotracheal tube and mechanically ventilated for 1 h. The animals were then randomly assigned to surfactant lavage (n = 12) with 15 ml/kg of diluted surfactant at a concentration of 5.4 mg phospholipid/ml administered in aliquots of 2 ml; or simple endotracheal suction (control n = 12) when the oxygenation index (OI) was ≥15. Changes in the arterial blood gases and the histomorphological and radiological appearances of the lungs were recorded. The OI and arterial/alveolar oxygen tension (a/A PO₂) of the surfactant lavage group improved significantly at 5 min post-treatment, and these improvements were observed throughout the ensuing 4 h of ventilation. There was significantly more solid content recovered by surfactant lavage compared with the control group (p = 0.0001). Radiologically, the post-treatment air space opacification scores of the lavage group were significantly lower compared with the control (p = 0.002). The post-treatment radiographs of the lavage-treated rabbits were rated by the radiologist, who was blinded to the treatment groups, as much improved in 5 and improved in 4, whereas the control rabbits were rated as much worse in 3 and worse in 4. Histological examination showed the lungs of the lavaged rabbits had significantly more normal airway (p < 0.0001), more fields showing completely normal airspace (p = 0.0001) and less fields showing severe overdistension with meconium (p = 0.0005). We concluded that lavage with diluted surfactant solution effectively washed out the meconium, improved gases exchanges, and improved the histological and radiological appearances in the rabbit model of MAS.

Effect of Added Salts or Polyols on the Cloud Point and the Liquid-Crystalline Structures of Polyoxyethylene-Modified Silicone

The effect of added salts (NaCl, Na2SO4, and NaSCN) or polyols (glycerin (Gly), 1,3-butanediol (1,3-BD), ethylene glycol (EG), and polyethylene glycol (PEG400)) on the hexagonal liquid-crystalline structure of polyoxyethylene-modified silicone was investigated by means of small angle X-ray scattering (SAXS). The effective cross-sectional area of the lipophilic part of the aggregate, as, in the hexagonal phase decreases upon the addition of salts, on one hand, lowering the cloud point in the dilute aqueous siloxane surfactant solutions. On the other hand, if added salt raises the cloud point, the as increases. Similar results were obtained in the case of the addition of polyols. Since the as mainly depends on the EO chain length, the above results are direct evidence that the hydration or dehydration of the EO chain is affected by these additives. The static fluorescence probe method was applied to the Gly and 1,3-BD systems using 8-anilino-1-naphthalene-sulfonic acid, ANS, to know the change in hydration of the EO chains. In the Gly system, the hydration of the EO chain monotonically decreases whereas 1,3-BD first increases the hydration and then decreases it at high 1,3-BD content. These results are very consistent with the SAXS and cloud temperature results.

Shear-Thickening Dilute Surfactant Solutions: Equilibrium Structure As Studied by Small-Angle Neutron Scattering

We have combined rheology and small-angle neutron scattering experiments to investigate dilute aqueous solution of cetyltrimethylammonium tosylate (CTAT). Rheology experiments have been performed under controlled strain conditions as function of concentration (φ = 0.05 − 1%) and temperature (T = 23−45 °C). At low surfactant concentration and under steady shear conditions, the CTAT exhibits a continuous increase of the apparent viscosity with increasing shear rates, also termed a shear-thickening transition. The critical shear rate for shear thickening varies strongly with the temperature according to an Arrhenius behavior, but very weakly with concentration. On the same solutions that were studied by rheology, neutron scattering was performed at rest to search for a correlation between the rheological features of the shear-thickening transition and the equilibrium micellar structure. We have found that (i) for all concentrations that display the thickening transition, the local morphology is that of cylindrical micelles, with a radius R = 21.0 ± 0.5 Å; (ii) all spectra exhibit a scattering correlation peak due to strong electrostatic repulsion between charged micelles; (iii) the shear-thickening transition in CTAT displays the same rheological features for solutions prepared either in the dilute (φ < φ*) or in the semidilute (φ* < φ < 0.8%) regimes.

Surfactant lavage for meconium aspiration syndrome: a pilot study.

Meconium aspiration syndrome (MAS) is a major cause of respiratory morbidity and mortality in term infants. We reported our pilot experience on the use of diluted bovine lung surfactant lipid extract solution (Survanta [Ross Laboratories, Ohio, USA]) as a tracheobronchial lavage fluid for the treatment of infants with severe MAS. Our goal was to establish the safety and the effectiveness of this procedure before organizing a randomized controlled trial. Six infants with severe MAS necessitating mechanical ventilation with an oxygen index of >/=15 within 6 hours of life recruited consecutively during a 11/2-year period were treated with tracheobronchial lavage with 15 mL/kg of diluted surfactant solution (Survanta) at a phospholipid concentration of 5 mg/mL administered in 2-mL aliquots. The outcome of treatment was assessed by comparison with 6 consecutive historic control infants with equally severe MAS of similar inclusion criteria retrospectively. The mean oxygen index, mean airway pressure, fraction of inspired oxygen, and arterial/alveolar oxygen tension ratio improved significantly within the first 48 hours after treatment in the lavage group. The duration of ventilation (mean +/- SEM, 55.3 +/- 4.6 hours vs 131 +/- 60 hours) and oxygen therapy (mean +/- SEM, 4.1 +/- 0.5 days vs 20.8 +/- 8.2 days) were also significantly reduced in the lavage-treated group compared with the control group. All 6 patients in the lavage group survived without sequelae whereas there were 2 deaths in the control group. The process of administering the surfactant lavage was well tolerated with no air leak complications. Our experience suggested that surfactant lavage seems to be an effective and safe method for treatment of severe MAS. A multicenter randomized control trial is indicated to further study the efficacy of this treatment.

Self-association and reverse hemimicelle formation at solid–water interfaces in dilute surfactant solutions

Using monodisperse anatase and hematite particles, such classical techniques as colloid stability, ζ potential and wettability measurements along with fluorescence spectroscopy show that anionic alkyl sulfate and sulfonate surfactants first associate into hemimicelles at the interface and cause the particles to begin to coagulate and to become hydrophobic. Maximum coagulation and hydrophobicity occur under conditions where the ζ potential is zero. At higher surfactant concentrations, the particles redisperse and regain their hydrophilicity. Upon reversal of the ζ potential, the adsorbed surfactant ions appear to form hemimicelles with reverse orientation or bilayers, at surfactant concentrations significantly lower than the critical micelle concentration. The results of these experiments correlate well with spectroscopic and adsorption measurements.

Mass transfer correlation in flotation of palm oil by colloidal gas aphrons

Colloidal gas aphrons (CGAs) are micron-sized bubbles, which are produced by stirring a dilute surfactant solution at a high speed. In this work, CGAs have been used to clarify oily wastewater by flotation technique. The CGAs sparging rate was a critical factor that governed the efficiency of the process. A model for the determination of the mass transfer coefficient is also developed for the purpose of process design.