Combined Effect Of Surfactants Research Articles

Dynamics of surfactant-laden drops in shear flow by lattice Boltzmann method

We developed and applied a diffuse interface lattice Boltzmann method for simulating immiscible liquids with soluble surfactants using a modified Ginzburg–Landau free energy functional. We first validated the approach through simulations of planar interfaces and drop equilibration in quiescent fluid. The proposed method accurately captures the phase and surfactant fields with diminishing spurious velocities of 10−6. We systemically examined the effects of capillary number, comparing viscous to surface forces, the combined effect of surfactant and viscosity ratio (λ) of the drop to the continuous phase, and the bulk surfactant load on the deformation and breakage in a shear flow. At a given capillary number (0.05<Ca<0.32), drop behavior is influenced by reduced surface tension, tip-stretching, Marangoni stresses, and surface dilution. These effects either promote (by tip-stretching) or hinder (via Marangoni stresses, surface dilution) the surfactant distribution at the interface, consequently affecting the final drop morphology. As Ca increases, the competition between the viscosity ratio and the presence of surfactant determines drops' topological changes. The presence of surfactants can overcome the effect of viscosity ratio (when 0.05≤λ≤1.7) and promote drop breakup, whereas highly viscous drops (either λ<0.05 or λ>1.7) do not break. Furthermore, high surfactant loads result in higher drop deformation and earlier drop breakup. In brief, our method successfully captures the dynamics of surfactant-laden drops in shear flow, elucidating the complex interplay between flow hydrodynamics and surfactant transport with 3D quantitative phase and surfactant concentration fields.

Marangoni flow and surfactant transport in evaporating sessile droplets: A lattice Boltzmann study

The circulatory Marangoni flow can alter the contact line deposition in evaporating colloidal droplets with pinned contact line. Marangoni flow can be induced by surfactants or thermal effects. Although both cases have been exclusively investigated, the combined effect of surfactant-induced and thermal Marangoni flows is still unknown. The lattice Boltzmann method is utilized to simulate droplet evaporation and corresponding Marangoni flow. Five equations for hydrodynamics, interface capturing, vapor concentration, temperature field, and surfactant transport are intrinsically coupled with each other. They are simultaneously solved in the lattice Boltzmann framework. A geometrical method is proposed to pin the contact line at the triple point. First, evaporation-induced and thermal Marangoni flows are successfully captured. By incorporating surfactant-induced effects, interesting flow patterns are observed. Considering the combined effect of surfactant and temperature gradient, maximum surfactant concentration and maximum temperature (local minima for surface tension) are found at the top and the edge of the droplet, respectively. The maximum surface tension is consequently located between them, and double-circulation flow is observed. If the thermal effect is eliminated, surfactant local concentrations intermittently converge to steady values so that the edge concentration becomes higher than the apex concentration. Until reaching the steady state, there are two patterns that the flow alternates between: one in the direction of the thermal Marangoni flow and the other in the opposite direction.

Insight into the mechanism of nanoparticle induced suppression of interfacial tension

The combined effect of surfactant and nanoparticles on the surface and interfacial tension is of great importance in various industrial processes. This study provides an insight into the combined effect of a non-ionic surfactant (Triton X-100 and Tween20) and SiO2 nanoparticles at the air–water interface using experimental and theoretical approaches. The surfactant concentration was kept constant at CMC, and nanoparticle concentration was varied from 0 wt% to 1.2 wt%. The results show that nanoparticles reduce the efficiency of Triton X-100 and Tween 20 surfactants at the air–water interface, mainly due to the adsorption of surfactants on NPs, which is also supported by the theoretical model. Furthermore, density functional theory simulations are conducted to understand the adsorption of the non-ionic surfactant on silica NPs with the variation in the degree of ionization of silica NPs. We have observed that the adsorption of the non-ionic surfactants on silica NPs reduces as the degree of ionization of NPs increases, which is in agreement with the experimental observations.

Improvement in the absorbency of ozone bleached cotton fabric by the addition of surfactant

The combined effect of surfactants with ozone bleaching process on the quality of cotton fabric was examined in this paper. The concentration of surfactants was varied between 0.01- 0.5 g/l in order to evaluate its effect on CIE whiteness, absorbency and strength of cotton fabric bleached by ozone. The maximum improvement in absorbency (1.07 s) and whiteness (WCIE 66.53) was achieved in the presence of anionic surfactant (0.01 g/l) at optimized experimental conditions. The strength properties of cotton fabric bleached by ozone in the presence of surfactant were also improved. Pollution load of ozone bleaching effluent even after adding surfactant was far less than conventional bleaching effluent. Statistically it was confirmed that surfactant addition significantly improved the whiteness and absorbency of ozone bleached cotton fabric.

Synergistic Effects of Sodium Iodide and Sodium Dodecyl Sulfate at Low Concentrations on Promoting Gas Hydrate Nucleation

Surfactants and/or salts at low concentrations are inherently relevant to gas hydrate formation in nature and industry. However, the combined effects of surfactants and salts at low concentrations on gas hydrate formation are poorly understood. Here, we aim to fill this gap of knowledge by examining the effects of sodium dodecyl sulfate (SDS) and sodium iodide (NaI) at millimolar concentrations on methane hydrate formation. We show that adding NaI to dilute SDS solutions reduces the induction time significantly, promoting gas hydrate nucleation. Meanwhile, adding NaI adversely reduces the growth of methane hydrate. Fundamental studies based on sum frequency generation spectroscopy indicate an electrostatically aligned water layer at the gas–SDS solution interface caused by the charged interface as a result of surface adsorption of dodecyl sulfate anions. This aligned interfacial water layer hinders the nucleation of gas hydrate at the gas–SDS solution interface. Added NaI diminishes the alignment of interfacial water, thereby favoring the nucleation of the gas hydrate. Even though, the adverse (inhibiting) effect of added NaI on the methane hydrate growth remains a puzzling observation that requires further investigations. This study sheds more light on gas hydrate formation in surfactant- and salt-containing systems that are important to many phenomena in nature and applications in the industry.

Transformation of Block Copolymer Nanoparticles from Ellipsoids with Striped Lamellae into Onionlike Spheres and Dynamical Control via Coupled Cahn-Hilliard Equations.

Annealing of block copolymers has become a tool of great importance for the reconfiguration of nanoparticles. Here, we present the experimental results of annealing block copolymer nanoparticles and a theoretical model to describe the morphological transformation of ellipsoids with striped lamellae into onionlike spheres. A good correspondence between the experimental findings and predictions of the model was observed. The model based on finding the steepest direction of descent of an appropriate free energy leads to a set of Cahn–Hilliard equations that correctly describe the dynamical transformation of striped ellipsoids into onionlike spheres and reverse onionlike particles, regardless of the nature of the annealing process. This universality makes it possible to describe a variety of experimental conditions involving nanoparticles underlying a heating process. A notable advantage of the proposed approach is that it enables selective control of the interaction between the confined block copolymer and the surrounding medium. This feature endows the model with a great versatility to enable the reproduction of several combined effects of surfactants in diverse conditions, including cases with reverse affinities for the block copolymer segments. A phase diagram to describe a variety of morphologies is presented. We employ the relationship between the temperature-dependent Flory–Huggins parameter and the width of the interfaces to account for changes in temperature due to the heating process. Simulation results correctly show how the transformation evolves as the temperature increases. This increment in temperature corresponds to progressively smaller values of the interfacial width. We anticipate that the proposed approach will facilitate the design and more precise control of experiments involving various kinds of annealing processes.

Behavior of silver nanoparticles in wastewater: systematic investigation on the combined effects of surfactants and electrolytes in model systems

pH, electrolytes and surfactants affected the stability of AgNPs in artificial test water system.

Effect of surfactant and mineralizer on the dielectric properties of zirconia nanocrsytals

The combined effect of surfactants (PVP/CTAB) and alkaline mineralizers (NaOH/NH4OH) on dielectric properties of zirconia nanocrystals is analyzed. It is found that, the stabilization of zirconia tetramers by surfactants and the rate of hydroxyl ions released by alkaline mineralizers have significant impact on the dielectric properties of nanocrystals. The PVP capped tetramers form highly conducting grains with insulating boundaries, whereas the grains of CTAB capped tetramers are highly insulating with conducting grain boundaries, as revealed by Nyquist plots. Consequently, the space charge polarization would be quite large in highly conducting grains resulting in higher dielectric constant values at lower frequencies. The higher dielectric constant of PVP capped nanocrystals is due to greater tetragonal coordination of 3d5/2 and 3d3/2 electrons of Zr4+ ions than that of CTAB capped nanocrystals. Further, the surface oxygen vacancies of PVP samples are higher, resulting in a high space charge polarization. The ESR signal corresponding to F+ centers appears stronger for PVP/NH4OH nanocrystals. Moreover, the larger ESR line width of PVP/NH4OH nanocrystals corresponding to more oxygen vacancies is in accordance with the inference attained from the XPS analysis.

Wettability of Complex Fluids and Surfactant Capped Nanoparticle-Induced Quasi-Universal Wetting Behavior.

Even though there are quite large studies on wettability of aqueous surfactants and a few studies on effects of nanoparticles on wettability of colloids, to the best of authors' knowledge, there is no study reported on the combined effect of surfactant and nanoparticles in altering the wettability. The present study, for the first time, reports an extensive experimental and theoretical study on the combined effect of surfactants and nanoparticles on the wettability of complex fluids such as nanocolloids on different substrates, ranging from hydrophilic with a predominantly polar surface energy component (silicon wafer and glass) to near hydrophobic range with a predominantly dispersive component of surface energy (aluminum and copper substrates). Systematically planned experiments are carried out to segregate the contributing effects of surfactants, particles, and combined particle and surfactants in modulating the wettability. The mechanisms and the governing parameters behind the interactions of nanocolloids alone and of surfactant capped nanocolloids with different surfaces are found to be grossly different. The article, for the first time, also analyzes the interplay of the nature of surfaces, surfactant and particle concentrations on contact angle, and contact angle hysteresis (CAH) of particle and surfactant impregnated colloidal suspensions. In the case of nanoparticle suspensions, the contact angle is observed to decrease for the hydrophobic system and increase for the hydrophilic systems considered. On the contrary, the combined particle and surfactant colloidal system shows a quasi-unique wetting behavior of decreasing contact angle with particle concentration on all substrates. Also interestingly, the combined particle surfactant system at all particle concentrations shows a wetting angle much lower than that of the only-surfactant case at the same surfactant concentration. Such counterintuitive observations have been explained based on the near-surface interactivity of the particle, fluid, and surfactant molecules based on effective slip length considerations. The CAH analyses of colloidal suspensions at varying surfactant and particle concentrations reveal in-depth physical insight into contact line pinning, and a unique novel relationship is established between the contact angle and differential energy for distorting the instantaneous contact angle for a pinned sessile droplet. A detailed theoretical analysis of the governing parameters influencing the wettability has been presented invoking the principles of DLVO (Derjaguin-Landau-Verwey-Overbeek), surface energy and interaction parameters influencing at the molecular scale, and the theoretical framework is found to support the experimental observations.

Partitioning of hexachlorobenzene in a kaolin/humic acid/surfactant/water system: Combined effect of surfactant and soil organic matter

Understanding the combined effect of soil organic matter (SOM) and surfactants on the partitioning of hydrophobic organic compounds in soil/water systems is important to predict the effectiveness of surfactant-enhanced remediation (SER). In the present study we investigate the partitioning of hexachlorobenzene (HCB) within a humic acid (HA)-coated kaolin/Triton X-100 (TX100)/water system, with special emphasis on the interaction between TX100 and HA, and their combined effect on HCB sorption. HA firstly enhanced then suppressed TX100 sorption to kaolin as the amounts of HA increased, while the addition of TX100 led to a consistent reduction in HA sorption. In the HA-coated kaolin/TX100/water system, TX100 played a primary role in enhancing desorption of HCB, while the role could be suppressed and then enhanced as HA coating amounts increased. Only at HA coating above 2.4%, dissolved HA outcompeted clay-bound HA for HCB partitioning, resulting in dissolved HA enhanced desorption. The presence of dissolved HA at these conditions further promoted the effectiveness of TX100 enhanced desorption. Despite a reduced TX100 sorption to clay was achieved due to the presence of dissolved HA, the effect on HCB desorption was comparatively slight. A reliable cumulative influence of HA and TX100 on HCB desorption was observed, although HCB desorption by HA/TX100 mixed was less than the sum of HA and TX100 individually. Our study suggests that for soils of high organic contents, the combined effect of SOM and surfactants on HOCs desorption can be applied to improve the performance of SER.

Adsorption of zinc(II) and cadmium(II) on soil layers in TLC in the presence of surfactant-containing mobile phases

Adsorption of Zn(II) and Cd(II) ions on soil TLC plates was studied using aqueous solutions of surfactants as mobile phases. The effects of decomposition of soil organic matter, cation saturation, soil pH, and sewage sludge on the hR F values (or adsorption) of Zn(II) and Cd(II) were investigated. Among these conditions, soil pH was the most important factor affecting adsorption of Zn(II) and Cd(II) ions by soil layers. Aqueous solutions of cationic (cetyltrimethylammonium bromide, CTAB), nonionic ( t -octylphenoxydecaethoxyethanol, Triton X-100), and anionic (sodium dodecyl sulfate, SDS) surfactants at different concentrations (below, near, and above their critical micelle concentrations, CMC) were tested as mobile phases to examine their effect on the efficiency of adsorption of zinc(II) and cadmium(II) by soil stationary phases. Furthermore, the combined effect of surfactants and fertilizers on the adsorption characteristics of Cd(II) and Zn(II) was also investigated. Fertilizers such as KCl and CaCl 2...

Combined effect of SLS and (SBE) 7M-β-CD on the solubilization of NSC-639829

Complexation and micellization are two effective ways of solubilizing drugs. In this study, the combined effect of surfactant and complexant on the solubilization of a poorly water soluble compound (NSC-639829) is investigated. With increasing concentration of sodium lauryl sulphate (SLS) in solutions of fixed concentration of (SBE) 7M-β-CD, the total solubility of the drug decreases linearly, reaches a minimum and then increases linearly. At each minimum, the molar ratio of SLS to (SBE) 7M-β-CD is close to unity. The above observation is attributed to the fact that the surfactant molecule competes with the drug to “fit” in the non-polar cyclodextrin cavity. The surfactant depletes cyclodextrin to form a 1:1 complex. Once the concentration of free SLS reaches the CMC, it starts forming micelles and hence, solubilizes the drug. A slight decrease of the solubilizing power is noticed in the presence of SLS/(SBE) 7M-β-CD complex. The combined use of two solubilizing agents, a surfactant and a complexant, results in a much lower solubility than when either one is used alone at the same concentration. The surfactant molecule acts as a competitive inhibitor in the solubilization of the drug by the complexant. Similarly the complexant “pulls” the surfactant out of solution, making it unavailable for solubilizing the drug.