Water Surfactant Solutions Research Articles

Dielectrophoretic integration of single- and few-layer graphenes

The dielectrophoretic integration of single- and few-layered graphenes from three distinct graphene suspensions is presented, enabling the parallel assembly of individual two-dimensional nanostructures at predefined locations. The first suspension is an aqueous solution of graphene oxide, the second is ultrasonically exfoliated pristine graphene in N-methyl-pyrrolidone (NMP), and the third is exfoliated graphene in surfactant-stabilized 1 wt % aqueous SDBS solutions. The most crucial aspect for the successful thin flake deposition is the solution quality of the exfoliated graphene. After dielectrophoresis, single-layer graphene oxide is placed between the electrodes, which, while initially insulating, recovers its electrical conductivity following thermal reduction. From the chemically unmodified graphene-NMP solutions, the directed assembly of electrically active few-layer graphene flakes is realized, with flake thicknesses in the range 8–30 nm. Liquid phase exfoliation in water-surfactant solutions yields significantly thicker flake dimensions from 50 to several 100 nm due to the higher enthalpy of mixing in the dispersion. To achieve single-layer pristine graphene dielectrophoretic deposition, higher solution qualities must be available, consisting largely of single-layer graphene sheets. The reported research provides an important framework for parallel fabrication approaches of graphene-based devices.

Role of Surfactants in Carbon Nanotubes Density Gradient Separation

Several strategies aimed at sorting single-walled carbon nanotubes (SWNT) by diameter and/or electronic structure have been developed in recent years. A nondestructive sorting method was recently proposed in which nanotube bundles are dispersed in water-surfactant solutions and submitted to ultracentrifugation in a density gradient. By this method, SWNTs of different diameters are distributed according to their densities along the centrifuge tube. A mixture of two anionic amphiphiles, namely sodium dodecylsulfate (SDS) and sodium cholate (SC), presented the best performance in discriminating nanotubes by diameter. We present molecular dynamics studies of the water-surfactant-SWNT system. The simulations revealed one aspect of the discriminating power of surfactants: they can actually be attracted toward the interior of the nanotube cage. The binding energies of SDS and SC on the outer nanotube surface are very similar and depend weakly on diameter. The binding inside the tubes, on the contrary, is strongly diameter dependent: SDS fits best inside tubes with diameters ranging from 8 to 9 A, while SC is best accommodated in larger tubes, with diameters in the range 10.5-12 A. The dynamics at room temperature showed that, as the amphiphile moves to the hollow cage, water molecules are dragged together, thereby promoting the nanotube filling. The resulting densities of filled SWNT are in agreement with measured densities.

Friction and heat transfer in drag-reducing surfactant solution flow through curved pipes and elbows

A study of drag-reducing flow in curved pipes was conducted. In contrast to earlier studies we show that if we use a modified definition of drag reduction that includes only the turbulence effects, we observe indeed the same level of drag reduction in both coiled and straight pipes. More complex results showing reduced drag reduction compared to curved pipes were achieved with elbows. Two elbows of different size and type were tested in turbulent flow of both water and drag-reducing surfactant solution. A more elaborate analysis was conducted for a half-inch threaded elbow with a ratio of curvature radius to diameter of 1.2. The pressure drop and heat transfer were measured in a section downstream from the elbow over a distance of x/ D = 130 in order to investigate the hydrodynamic and thermal developments of the flow. The pressure drop coefficient of the elbow was calculated for water and a surfactant solution, based on the total increase in pressure drop in the system due to the presence of the elbow. For a larger welded elbow of 6″ diameter some drag reduction was measured for the surfactant solution.

Using Electrocapillarity to Measure the Zeta Potential of a Planar Hydrophobic Surface in Contact with Water and Nonionic Surfactant Solutions

A method is introduced for determining the zeta potential of planar surfaces by combining electroosmosis and capillarity. In this method, an electric field is applied across the channel, which is filled with aqueous solution seeded with fluorescent tracer particles. Some excess liquid is applied on both ends of the channel, which bulges out and modulates the capillary force across the channel by adjusting its curvature. While the velocity profile in the channel approaches steady state, a balance of the electroosmotic stress and Laplace pressure difference is achieved across the channel. However, as soon as the electric field is turned off, a Poiseuille flow develops in the channel due to the difference in the curvatures of the liquid bulges. We show that the measurement of the centerline velocity of the liquid inside the channel is enough to deduce the zeta potential of the surface. Utilizing this technique, the zeta potential of a hydrophobic glass surface (silanized by n-hexadecyltrichlorosilane, HC-16) has been measured to be -52.2 +/- 7.7 mV in distilled deionized water, which is in close agreement with the literature values. This technique has also been used to estimate the zeta potential of the HC-16 surface (zeta w(HC-16)), in the presence of the aqueous solutions of polyoxyethylene (23) lauryl ether (Brij 35). The zeta potential here at first becomes more negative than that in pure water, it stays flat for a while, and then it continues to become less negative as the concentration of the surfactant increases above the critical micelle concentration (CMC). This effect, where changes take place beyond the CMC but not below it, leads to a complementary Gibbs plot, where all the changes occur below the CMC but not above it. It is conjectured that the scavenging of hydroxyl ions by the Brij 35 micelles may be responsible for the observed effect.

Quantitative analysis of dispersion and doping of individual carbon nanotubes in water based solutions using absorption and Raman spectroscopy

AbstractThe concentration dependence of the dispersion of carbon nanotubes in water surfactant solution is monitored using absorption and Raman spectroscopy revealing a debundling below ∼0.07 g/l. A quantitative analysis of the doping of individual carbon nanotubes in surfactant at this concentration is conducted by varying the pH from 1 to 13 and monitoring the Raman spectrum. Mixed Gaussian and Lorentzian line shapes were fitted to the radial breathing modes and using a simple protonation model, an equilibrium constant Kp was obtained for each RBM. The protonation rate was related to the optical band gap of the tubes and the number of protons acting per entity was also calculated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dispersion of silicone oil in water surfactant solution: Effect of impeller speed, oil viscosity and addition point on drop size distribution

The preparation of dilute aqueous silicone oil emulsions has been investigated with particular attention to the effect of oil viscosity (0.49–350 mPa s), impeller selection (equal diameter Sawtooth and pitched blade turbines) and the method of addition of the oil. Emulsification was found to be sensitive to how the oil was added to the vessel with narrower drop size distributions and smaller Sauter mean diameters, d 32, obtained when the oil was injected into the impeller region. The equilibrium values were also attained in a shorter time with the equilibrium d 32 ∝ We −0.6. For addition of the oil to the surface the relationship was weaker with equilibrium d 32 ∝ We −0.4. The viscosity group was particularly useful in describing the behaviour of equilibrium particle sizes for different viscosity oils and also for viscosity changes arising from different process temperatures. An unexpected result is that the Sawtooth impellor proved to be more energetically efficient at drop break-up producing smaller droplets than the Pitched Bade Turbine. This result is particularly interesting since the power number for the latter is larger and therefore for equivalent operating conditions should produce smaller drop sizes. We suggest that one possible reason is that the local shear rates for the Sawtooth impellor are larger. Another possible reason is that the Sawtooth geometry provides more points where the local shear rates are high.

Investigation of Sodium Dodecyl Benzene Sulfonate Assisted Dispersion and Debundling of Single-Wall Carbon Nanotubes

The dispersion limit of HiPco single-wall carbon nanotubes (SWCNT) in 1% by weight sodium dodecyl benzene sulfonate (SDBS) assisted dispersions in water is reported. The starting concentration of the tubes in water surfactant solution was 5 mg/mL which was diluted sequentially by a factor of 2 down to 1.2 × 10-3 mg/mL. Sonication and centrifugation were performed to obtain a homogeneous dispersion of HiPco SWCNTs in water surfactant solution. Concentration-dependent absorption and Raman spectroscopic studies were used to analyze the SWCNTs behavior in water-based solution, and atomic force microscopy (AFM) was employed to examine the aggregation state of the nanotubes over the concentration range. Both spectroscopic techniques demonstrate a clear concentration below which the nanotube bundles become significantly dispersed in the solution. The concentration limit at which debundling starts was found to be 0.07 ± 0.03 mg/mL. The dispersion behavior and optical parameters determined are compared with those ...

Vertical two-phase flow regimes and pressure gradients under the influence of SDS surfactant

Two-phase gas/liquid flows in vertical pipes have been systematically investigated. Water and SDS surfactant solutions at various concentrations were used as the working fluids. In particular, we focus our work on the influence of surfactant addition on the flow regimes, the corresponding pressure gradients, and the bubble sizes and velocity. Adding the surfactant lowers the air critical Reynolds numbers for the bubble–slug flow and the slug flow transitions. The pressure gradients of SDS solutions are lower than those of pure water especially in the slug flow and the slug–churn flow regimes, implying turbulent drag reduction. At low Re air, the bubble sizes of the surfactant solution are lower than those of pure water due to the increase in viscosity. With increasing and at high Re air, the bubble sizes of the SDS solution become greater than those of pure water which is attributed to the effect of surface tension.

Flow boiling CHF enhancement with surfactant solutions under atmospheric pressure

Surfactant effect on CHF (critical heat flux) was determined during water flow boiling at atmospheric pressure in closed loop filled with solution of tri-sodium phosphate (TSP, Na3PO4·12H2O). TSP was added to the containment sump water to adjust pH level during accident in nuclear power plants. CHF was measured for four different water surfactant solutions in vertical tubes, at different mass fluxes (100–500kg/m2s) and two inlet subcooling temperatures (50°C and 75°C). Surfactant solutions (0.05–0.2%) at low mass flux (∼100kg/m2s) showed the best CHF enhancement. CHF was decreased at high mass flux (500kg/m2s) compared to the reference plain water data. Maximum increase in CHF was about 48% as compared to the reference data. Surfactant caused a decrease in contact angle associated with an increase of CHF from surfactant addition.

The growth kinetics of hydrate film on the surface of gas bubble suspended in water or aqueous surfactant solution

A novel experimental method to study the hydrate formation kinetics on the gas/water interface was presented and, using this method, the two-dimensional growth kinetic data of hydrate film on the surface of quiescent methane gas bubble suspended in pure water, natural water and natural water added with different contents of sodium dodecyl sulfate (SDS) were measured and compared. The experimental results showed that the presence of the low dose of ions in natural water appreciably inhibited the hydrate formation; the presence of SDS promoted the hydrate growth when its concentration was lower than 1000 mg/L while it inhibited the hydrate formation beyond this region, the concentration of SDS corresponding to the most efficient promotion was determined to be 500 mg/L or so; the presence of low-dose ions in the natural water has little negative influence upon the promotion efficiency of SDS. A two-parameter kinetic model was developed to correlate the growth rates of hydrate films in different aqueous solutions consistently, where the dimensionless Gibbs free energy difference of hydrate formation reaction was chosen as driving force. Good agreement between calculated results and experimental data was achieved and only one parameter was found to be SDS concentration dependent. The mechanism that the presence of SDS affects the hydrate formation rate was discussed based on the experimental and theoretical results with some new insights. Additionally, the three-dimensional growth of hydrate shell covering the gas bubble was studied morphologically and a series of interesting phenomena were observed and discussed.

Polymer Anchoring Layer for Atomic Force Microscopy Studies of Nanoparticle–Substrate Interactions

An immiscible polymer blend of poly(glycidyl methacrylate) and poly(vinylpyridine), PGMA/PVP, was used as an anchoring layer to attach silica nanoparticles to an oxidized silicon wafer surface. The stability of the arrays of colloidal particles was studied in pH 4 and pH 10 buffer solutions, deionized (DI) water, and nonionic surfactant solution. The array was determined to be stable. Attachment of the nanoparticles to one‐component homogeneous PGMA and PVP films was also studied in order to determine the role of each polymer in the anchoring layer. Virtually no particles were adsorbed on the surface modified with PGMA. The nanoparticles could be adsorbed on PVP, but the integrity of the polymer layer was destroyed in the environment used for adsorption, i.e., a dispersion of nanoparticles at pH 10. Measurement of adhesion between the nanoparticles attached to the anchoring layer and the glass substrate were performed in aqueous media having different pH values using a colloidal probe atomic force microscopy (AFM) technique. In Commemoration of the Contributions of Professor Valery P. Privalko to Polymer Science.

Behavior and Surrounding Liquid Motion of a Single Bubble Rising in Water-Surfactant Solutions

The effects of a surfactant on a single ascending bubble motion and its surrounding liquid motion were investigated using 1-pentanol and purified water systems. An ellipsoidal bubble (2.8 mm in equivalent diameter) was examined in a quiescent liquid. The bubble motion was visualized using a high-speed video camera. As a result, changes of the amplitude and frequency of the bubble trajectory were observed at a 1-pentanol concentration of 150ppm. At 500ppm, “small initial deformation” due to the strong damping effect was caused by adsorption of the surfactant on the bubble surface. The bubble velocity became low as reported by the other researchers. Furthermore, the liquid motion in the vicinity of the bubble was visualized via PIV method (Particle Image Velocimetry) with recursive cross correlation PIV algorithm. As a result, the difference in vorticity associated with the strength of the shed vortex was observed at the inversion points at which the bubble changes the direction of the zigzag motion. The difference affects the change of the amplitude and frequency of the bubble trajectory. An effect of the boundary condition changing from free-slip to no-slip in the contaminated system yields this difference.

Compression of Langmuir Films Composed of Fine Particles: Collapse Mechanism and Wettability

The collapse mechanism of microparticulate Langmuir films was studied experimentally in the present work. Using a Wilhelmy film balance, surface pressure vs area isotherms were determined, and the particle removal during the compression was examined by video-microscope and by naked eye. Upon compressing partially wettable 75 microm diameter surface modified glass beads at liquid (water or aqueous surfactant solution)-air (or n-octane) interfaces, different collapse mechanisms were visualized depending on the wettability of the particles. At low contact angles (below 40 degrees ) irreversible particle removal was observed as a consequence of a particulate line-by-line collapse mechanism. At higher contact angles a buckling-type collapse mechanism was revealed without particle removal from the liquid interface. In the case of irreversible particle removal we assessed the contact angles from the nondissipative part of the isotherm. These values were found to be in reasonable agreement with those determined directly on the beads.

Preparation of metal oxide-based nanomaterials using nanosecond pulsed laser ablation in liquids

Numerous experiments for nanomaterial fabrication using pulsed laser ablation in liquid have been reported. Most studies have focused on the formation of noble-metal nanoparticles and their surface plasma-resonant optical properties. This short review highlights the fabrication of metal oxide-based nanomaterials such as oxide and hydroxide nanoparticles, as well as layered nanocomposites, via nanosecond pulsed laser ablation of metallic target materials in water and aqueous surfactant solutions. These crystallized oxide-based nanomaterials are formed through the ejection of ablated species with extremely high density and high kinetic energy followed by oxidation in the liquid.

Bubble growth in saturated pool boiling in water and surfactant solution

The presence of surfactant additives in water was found to enhance the boiling heat transfer significantly. The objective of the present investigation is to compare the bubble growth in water to that of a surfactant solution with negligible environmental impact. The study was conducted at two values of heat fluxes to clarify the effect of the heat flux on the dynamics of bubble nucleation. The bubble growth under condition of pool boiling in water and non-ionic surfactant solution was studied using high speed video technique. The bubble generation was studied on a horizontal flat surface; and the natural roughness of the surface was used to produce the bubbles. We did a quantitative analysis of single bubble growth, in saturated nucleate pool boiling of water, with constant wall heat flux q = 10 and 50 kW/m 2. The captured images showed that the bubble shape is close to axially-symmetric and vertically non-symmetric. At heat flux of q = 10 kW/m 2 the life-time and the volume of bubble growth-rate in surfactant solution did not differ significantly from those of water. The time behavior of the contact angle of bubble growing in surfactant solution is qualitatively similar to that of water. At a heat flux of q = 50 kW/m 2, boiling in surfactant solution, when compared with that of pure water, was observed to be more vigorous. Surfactant promotes activation of nucleation sites; the bubbles appeared in a cluster mode; the life-time of each bubble in the cluster is shorter than that of a single water bubble. The detachment diameter of water bubble increases with increasing heat flux, whereas analysis of bubble growth in surfactant solution reveals the opposite effect: the detachment diameter of the bubble decreases with increasing heat flux.

Swirling Flow of a Viscoelastic Fluid With Free Surface—Part I: Experimental Analysis of Vortex Motion by PIV

The swirling flows of water and CTAC (cetyltrimethyl ammonium chloride) surfactant solutions (50-1000ppm) in an open cylindrical container with a rotating disc at the bottom were experimentally investigated by use of a double-pulsed PIV (particle image velocimetry) system. The flow pattern in the meridional plane for water at the present high Reynolds number of 4.3×104 differed greatly from that at low Reynolds numbers, and an inertia-driven vortex was pushed to the corner between the free surface and the cylindrical wall by a counter-rotating vortex caused by vortex breakdown. For the 1000ppm surfactant solution flow, the inertia-driven vortex located at the corner between the bottom and the cylindrical wall whereas an elasticity-driven reverse vortex governed the majority of the flow field. The rotation of the fluid caused a deformation of the free surface with a dip at the center. The dip was largest for the water case and decreased with increasing surfactant concentration. The value of the dip was related to determining the solution viscoelasticity for the onset of drag reduction.

Swirling Flow of a Viscoelastic Fluid With Free Surface—Part II: Numerical Analysis With Extended Marker-and-Cell Method

In Part I [Wei et al., 2004, 2004 ASME Int. Mech. Eng. Conference], we presented the experimental results for swirling flows of water and cetyltrimethyl ammonium chloride (CTAC) surfactant solution in a cylindrical vessel with a rotating disk located at the bottom for a Reynolds number of around 4.3×104 based on the viscosity of solvent. For the large Reynolds number, violent irregular instantaneous secondary flows at the meridional plane were observed by use of a particle image velocimetry system. Because of the limitations of our computer resources, we did not carry out direct numerical simulation for such a large Reynolds number. The LES and turbulence model are alternative methods, but a viscoelastic LES/turbulence model has not yet been developed for the surfactant solution. In this study, therefore, we limited our simulations to a laminar flow. The marker-and-cell method proposed for Newtonian flow was extended to the viscoelastic flow to track the free surface, and the effects of Weissenberg number and Froude number on the flow pattern and surface shape were studied. Although the Reynolds number is much smaller than that of the experiment, the major experimental observations, such as the inhibition of primary and secondary flows and the decrease of the dip of the free surface by the elasticity of the solution, were qualitatively reproduced in the numerical simulations.

Spreading, Evaporation, and Contact Line Dynamics of Surfactant-Laden Microdrops

An optical technique based on the reflectivity measurements of a thin film was used to experimentally study the spreading, evaporation, contact line motion, and thin film characteristics of drops consisting of a water-surfactant (polyalkyleneoxide-modified heptamethyltrisiloxane, called superspreader) solution on a fused silica surface. On the basis of the experimental observations, we concluded that the surfactant adsorbs primarily at the solid-liquid and liquid-vapor interfaces near the contact line region. At equilibrium, the completely wetting corner meniscus was associated with a flat adsorbed film having a thickness of approximately 31 nm. The calculated Hamaker constant, A = -4.47 x 10(-)(20) J, shows that this thin film was stable under equilibrium conditions. During a subsequent evaporation/condensation phase-change process, the thin film of the surfactant solution was unstable, and it broke into microdrops having a finite contact angle. The thickness of the adsorbed film associated with the drops was lower than that of the equilibrium meniscus. The drop profiles were experimentally measured and analyzed during the phase-change process as the contact line advanced and receded. The apparent contact angle, the maximum concave curvature near the contact line region, and the convex curvature of the drop increased as the drop grew during condensation, whereas these quantities decreased during evaporation. The position of the maximum concave curvature of the drop moved toward the center of the drop during condensation, whereas it moved away from the center during evaporation. The contact line velocity was correlated to the observed experimental results and was compared with the results of the drops of a pure alcohol. The experimentally obtained thickness profiles, contact angle profiles, and curvature profiles of the drops explain how the surfactant adsorption affects the contact line motion. We found that there was an abrupt change in the velocity of the contact line when the adsorbed film of the surfactant solution was just hydrated or desiccated during the phase-change processes. This result shows the effect of vesicles and aggregates of the surfactant on the shape evolution of the drops. For these surfactant-laden water drops, we found that the apparent contact angle increased during condensation and decreased during evaporation. However, for the drop of a pure liquid (n-butanol and 2-propanol) the apparent contact angle remained constant at a constant velocity during condensation and evaporation. The contact line was pinned during the evaporation and spreading of the surfactant-laden water drops, but it was not pinned for a drop of a pure alcohol (self-similar shape evolution).

The analysis of phenomena and factors having an effect on the sedimentation stability and rheology of water-based dispersions of MMA/BA/MAA copolymer in xylene

This paper presents essentially the results of sedimentation and rheological studies on aqueous dispersed systems of copolymer methyl methacrylate with butyl acrylate and methacrylic acid (MMA/BA/MAA) in a xylene solution. Non-ionic surfactants such as oxyethylenated unsaturated fatty alcohol, lauryl alcohol and oxyethylenated amines were used as well as the thickening agents: polyvinyl alcohol, sodium salt of carboxymethylcellulose (CMC-Na) and water-soluble polyurethane oligomer. The properties of surfactant water solutions were determined with the use of tensiometric and viscometric methods. The structure of the obtained copolymer was analysed by gel chromatography. The sedimentation experiment was a basic test used to determine the stability of aqueous dispersions of the obtained copolymer in xylene. It consisted in determining types of phases occurring in sedimentation equilibrium. The formation of a foamed copolymer phase was the most interesting phenomenon. A rheological test was carried out by using the so-called stable phase and was aimed to define maximum viscosity, pseudoplasticity and activation energy of a viscous flow. Moreover, the reduced viscosity, a limiting viscosity number and the Huggins constant were also determined. The relationships between these quantities were established indicating the dependences, which were the best interpretation describing interactions between particles in the dispersed system. Basing on rheological and sedimentation tests, the most probable mechanisms of stability in systems of this type were determined. The factors reducing their stability and concerned with flocculation and coalescence of particles have been defined.

Heat transfer characteristics of water and APG surfactant solution in a micro-channel heat sink

The steady increase in internal heat production of cost and high performance electronic components has lead researchers to seek improved ways to remove the heat generated. Single-phase liquid flow has been considered as a potential solution for solving this cooling problem. However, when considering that any solution needs to be of low cost and low mass fluxes and yet retain low temperature gradients across the electronic components, it seems that two-phase boiling flow is preferred. Surfactant solutions have been introduced in connection with enhancement of the boiling processes. We investigated the effects of surfactant solution flows through a micro-channel heat sink. The experimental setup included a high-speed IR radiometer and a CCD camera that were used to characterize the test module. The module consisted of inlet and outlet manifolds that distributed surfactant solutions through an array of 26 parallel micro-channels. The experimental results have shown that there exists an optimal solution concentration and mass flux for enhancing heat removal. Surfactant solution boiling flows were also found to stabilize the maximum and average surface temperatures for a wide range of applied heat fluxes. In addition, the use of surfactant solutions at low mass fluxes has led to CHF enhancement when compared to regular water flows. In the last part of this work, possible explanations for the observed non-ionic surfactant effects are presented.