Absence Of Surfactant Research Articles

Controlling the growth of fullerene C60 cones under continuous flow.

Micromixing of an o-xylene solution of C60 with N-N-dimethylformamide (DMF) at room temperature under continuous flow in a vortex fluidic device (VFD) results in the formation of symmetrical right cones in high yield with diameters 0.5 to 2.5 μm, pitch angle 25° to 55° and wall thickness 120 to 310 nm. Their formation is in the absence of surfactants and any other reagents, and is scalable. The cones are formed at specific operating parameters of the VFD, including rotational speed, flow rate and concentration, and varying these results in other structures such as grooved fractals. Other aromatic solvents in place of o-xylene results in the formation of rods, spicules and prisms, respectively for m-xylene, p-xylene and mesitylene.

Preparation and Investigation of Foaming Amphiphilic Fluorinated Nanoparticles for Enhanced Oil Recovery.

Amphiphilic nanoparticles have attracted increasing interest as Pickering emulsifiers owing to the combined advantages of both traditional surfactants and homogeneous particles. Here, foaming amphiphilic fluorinated nanoparticles were prepared for enhanced oil recovery by the toposelective surface modification method. The structure and properties of amphiphilic nanoparticles were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, a laser diffraction method, fluorescence microscopy, a pendant drop tensiometer, and foamscan. It was found that the amphiphilic fluorinated nanoparticles exhibited significant interfacial activity at the air–water interface and generated stabilized aqueous foams against coalescence and drainage even in the absence of surfactants. When the particle concentration reached 0.6 wt %, the adsorption of the amphiphilic nanoparticles at the interface was saturated and the equilibrium surface tension dropped to around 32.7 mN/m. When the particle concentration reached 0.4 wt %, the Gibbs stability criterion was fulfilled. The amphiphilic nanoparticles foam system has a better plugging capacity and enhanced oil recovery capacity. The results obtained provide fundamental insights into the understanding of the self-assembly behavior and foam properties of amphiphilic fluorinated nanoparticles and further demonstrate the future potential of the amphiphilic nanoparticles used as colloid surfactants for enhanced oil recovery applications.

Effect of Surfactants and Carbon Nanomaterials on the Electroflotation Extraction of the Disperse Phase of Cobalt Hydroxides

The effect of surfactants and carbon nanomaterials (CNMs) on the electroflotation extraction of the disperse phase of cobalt(II) and (III) hydroxides at pH 6 and pH 10 was studied. It is shown that at pH 6 in the absence of surfactants, the efficiency of cobalt extraction in various electrolytes is low and does not exceed 15–25%. In the surfactant–CNM–electrolyte system, the degree of extraction α increases in the chloride, nitrate, and sulfate solutions compared with the solutions containing no surfactants. The electroflotation extraction of cobalt was more efficient at pH 10: α reached 80–96% in the absence of surfactants, 70–97% in the surfactant–electrolyte system, and 60–97% in the surfactant–CNM–electrolyte system. The optimum conditions of the electroflotation extraction of cobalt hydroxides from solutions containing various inorganic electrolytes were determined. The effect of the sodium chloride content on the degree of cobalt extraction at pH 6 was studied. When the NaCl concentration increased from 0 to 10 g/L, the efficiency of cobalt extraction increased to 92%; when the flocculant was added and an additional stage of filtration was used, cobalt was extracted almost completely.

Impact of an insoluble surfactant on the thresholds of evaporative Bénard-Marangoni instability under air.

It is known that the addition of an insoluble surfactant to a Bénard-Marangoni (BM) layer heated from below or cooled from above can give rise to a supplementary, oscillatory mode of instability. Here the objective is to see how exactly this plays out in the framework of a recently studied and experimentally tested case of a non-long-wavelength BM instability driven by diffusion-limited evaporation into air in isothermal surroundings. Linear stability analysis is accomplished within a now standard reduction to a one-sided model. In the absence of surfactant, we just recover the classical Pearson problem, albeit with an evaporation-specific wavenumber-dependent Biot number potentially attaining large values for strongly volatile liquids. Adding a surfactant not only sharply stabilizes the monotonic Pearson-like mode, but also leads to a more dangerous oscillatory mode, a parametric study of which is here undertaken. Although slanted towards the evaporative case, the present study is also of interest from the general viewpoint of the Pearson problem + an insoluble surfactant, the results for which are scarce in the literature without being obscured by further effects. In particular, an asymptotic analysis based on small interfacial Lewis numbers (diffusion coefficients) is undertaken near the codimension-2 point.

Diesel engine fuel consumption and emission analysis using steam generated non-surfactant water-in-diesel emulsion fuel

Efforts in making water in diesel emulsion (W/D) with the absence of surfactant have been developed to address the issues of long-term stability and the dependence on surfactants. This paper discusses an alternative formation method of a non-surfactant W/D, e.g. by steam condensation. By injecting steam into a batch of colder diesel fuel, fine water droplets are formed and suspended in the fuel forming an emulsion. The droplets are confirmed to be in the size range of hundreds of nanometers. The emissions of NOx is reduced by a maximum of 71%, whereas the CO and UHC emissions are increased by maximum respectively 180% and a surprising 517%. Not less interesting is the lower BSFC which was measured at a maximum reduction of 18.4%. These results on emission analysis together with the brake specific fuel consumption confirm this method to resemble the combustion behaviour of a conventional emulsion fuel of lower NOx and BSFC, yet higher CO and UHC

In-situ polyurethane/polyacrylate microemulsion formation: the effects of acrylic content in wood coating application

In-situ surfactant-free emulsion polymerization was utilized to prepare polyacrylate/polyurethane (PUA) microemulsions in the absence of surfactant and organic solvent. For this purpose, PUA with higher acrylate content was successfully prepared, with the aim to reduce the coating cost. The dynamic light scattering results showed that the particle size of PUA microemulsion displayed a unimodal distribution and the particle size was ranged from 33 to 61 nm. In comparison with PUA prepared with conventional miniemulsion polymerization, the particle size distribution coefficient dropped by one order. Atomic force microscopy, together with thermogravimetric analyzer, demonstrated good compatibility and interaction between PU and acrylic components, and no phase separation was detected even at 58 wt% acrylic content. With the incorporation of acrylic component, the thermal stability and maximum stress were improved. The maximum stress greatly increased from 4.6 to 30.9 MPa, and the maximum stress of in-situ PUA was nearly three times larger than that of PUA prepared by miniemulsion polymerization. The effects of acrylic content on water resistance, pencil hardness, adhesion, and impact strength of wood coating were evaluated. With increasing the acrylic content, the water resistance and pencil hardness increased, though the impact strength of in-situ PUA films was slightly reduced.

CTAB-assisted sol-microwave method for fast synthesis of mesoporous TiO2 photocatalysts for photocatalytic conversion of glucose to value-added sugars

Fabrication technique is an important factor for development of catalysts. Titanium dioxide (TiO2) is one of efficient photocatalysts. In this work, we firstly report the fabrication of TiO2 nanoparticles by sol-microwave method with cetyltrimethylammonium bromide (CTAB) surfactant. Absence of surfactant, microwave treatment significantly reduced the cluster sizes of TiO2, but high aggregations of TiO2 particles were observed. CTAB has great impact on morphology, cluster size and mesoporous structure of TiO2. Therefore, surface area of TiO2 synthesized by sol-microwave method with 0.108M CTAB increased from 15.97 to 37.60m2/g. Photocatalytic activity of TiO2 was tested via the glucose conversion to produce value-added chemicals (gluconic acid, xylitol, arabinose and formic acid). It was found that surface area, mesoporous structure and pore size of TiO2 are crucial properties for glucose conversion and product distribution. From the reaction test, 0.108M CTAB/MW-TiO2 achieved the highest glucose conversion (62.28%).

Kinetic and mechanistic studies on the oxidation of d-glucose by MnO2 nanoparticles. Effect of microheterogeneous environments of CTAB, Triton X-100 and Tween 20

The kinetics of electron transfer reaction between D-glucose and MnO2 nanoparticles has been studied in weakly acid medium. In the colloidal solution of MnO2, ultrafine nanoparticles of MnO2 remain supported on two-dimentional gum acacia sheets in the form of crumbled paper ball assuming the form of spherical particulates of size 60–200nm as detected by TEM. The nanoparticles are found to be amorphous. Apart from the inhibition, due to adsorption of reaction products on the surface of the nanoparticles, the reaction is first order with respect to MnO2, but complex order with respect to glucose as well as H+. Glucose is oxidized to δ-lactone through a one-step two-electron transfer process and the latter is rapidly hydrolyzed to gluconic acid. The oxidation of glucose in absence of surfactant is entropy-controlled. In the presence of surfactants of cetyl trimethyl ammonium bromide (CTAB), Triton X-100 (TX-100) and Tween 20, the reaction rate passes through a maximum around the CMC. Both the reactants are distributed between the aqueous and the micellar pseudophases and then react, following Berezin’s model. Ion-dipole interaction and H-bonding appear to play an important role in the binding between glucose and the surfactant molecules while protonated MnO2 remains at the periphery of the Stern layer within the micelle. The binding of glucose with the surfactants is controlled by the entropy changes associated with the glucose-water interaction, micelle-water interaction and glucose-micelle interaction.

Size-Tunable and Crystalline BODIPY Nanorods for Bioimaging.

Constructing organic nanorods with a uniform and tunable size is challenging. Herein, we fabricated borondipyrromethene (BODIPY) nanorods (BDP-NRs) via a simple single-step reprecipitation method in the absence of surfactants or adjuvants. The length and aspect ratio of the BDP-NRs could be tuned by varying the concentration of BDP. In addition, the obtained BDP-NRs are crystalline and stable in aqueous solution for several weeks. The formation mechanism of BDP-NRs was investigated in detail and ascribed to the crystallinity-induced assembly. More important, the BDP-NRs demonstrated efficient cellular uptake by living cells and a better imaging performance than free BDP, which contribute to a decrease in dosage of fluorescent dyes for bioimaging. This simple fabrication process with the ability to generate nanorods may open a new avenue in the development of organic fluorescence nanomaterials.

Influence of micellar aggregates on oxidative degradation of β-cyclodextrin by alkaline permanganate: A kinetic and mechanistic study of inclusion complex

Kinetics of MnO4−-β-cyclodextrin (BCD) redox reaction has been studied spectrophotometrically in presence of anionic surfactant micelles of sodium dodecyl sulfate (SDS) and cationic surfactant micelles of cetyltrimethylammonium bromide (CTAB) in alkaline medium. The rate of the reaction shows first order dependence on [MnO4−] and fractional order dependence on [BCD], [OH−] in the presence of both CTAB and SDS. Both the surfactants CTAB and SDS shows rate inhibition effects. Inhibition effect of CTAB was observed above critical micelle concentration (CMC) while that of SDS was observed below the CMC. Oxidised products were confirmed by FT-IR and 1H NMR spectral techniques. Reaction between SDS and BCD shows inclusion complex formation which was confirmed by conductivity measurements. The observed results were discussed in terms of Menger and Portnoy’s model for micellar inhibition. Activation parameters have been evaluated using Eyring equation. The effect of added salts (KCl, KBr, NaNO3 and Na2SO4) on the reaction has been studied. The effect of ionic strength and dielectric constant on the rate of reaction has been studied in the absence of surfactants. Probable reaction mechanism, in agreement with the observed kinetic results has been proposed and discussed.

Surfactant effect on interaction of rising bubble and particle in a liquid subjected to vibrations

The paper investigates the surfactant effect on the interaction of solid particle and gas bubble in a liquid subjected to vibrations. Surfactant transport between the bubble surface and the surrounding liquid is limited by the adsorption-desorption process. The particle is subjected to the Stokes, Basset and buoyancy forces, and average force related to the inhomogeneity of the pulsational field. The problem is solved numerically. It is found that in the presence of surfactant, the impact of vibrations on the particle-bubble collision is weaker than in the absence of surfactant. Thus, higher vibrations intensity is needed for increasing the collision efficiency, together with a higher consumption in energy.

Surfactant-free synthesis of sub-stoichiometry tungsten oxide nanoparticles and their use as anode buffer layers in organic solar cells

A surfactant-free synthesis of small-sized tungsten trioxide is presented. Nanoparticles with an average size of 4.6 ± 1.5 nm are prepared via hot-injection techniques in ethanol. Due to the reducing properties of ethanol, a sub-stoichiometry composition WO3-x (x∼0.4) is obtained. The partial reduction of W+VI to W+V becomes visible in the bluish color of suspensions and powder samples and in optical spectroscopy (UV-Vis). The nanoparticles are further characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDXS) and infrared spectroscopy (FT-IR). Due to their small size, their high colloidal stability and the absence of surfactants, layers from the as-prepared WO3-x nanoparticles are ideally suited to form anode buffer layers in organic solar cells. Exemplary solar cells show good power conversion efficiency of 6.3%.

The effect of surfactants in the silsesquioxane solution for LbL films assembly

The interaction of surfactants and hydrophobic polymers in solution has attracted substantial interest due to the broad application in industry. In this study, the interactions of the nonionic surfactant polyethylene glycol-p-(1,1,3,3 tetramethylbutyl)-phenyl ether (Triton X) and anionic surfactant sodium dodecyl sulfate (SDS) with a cationic polymer 3-chloride-n-propylpyridinium silsesquioxane (SiPy+Cl−) and their effects on the layer-by-layer (LbL) film assembly with nickel tetrasulfonated phthalocyanine (NiTsPc) have been analyzed by surface tension, viscosity, and Brewster angle microscopy. As Triton X and SDS surfactants are inserted in the solution containing the polycation SiPy+Cl−, they are immediately incorporated in the hydrophobic nanodomains present in the silsesquioxane skeleton. The association between polyelectrolytes and oppositely charged surfactants starts at very low surfactant concentrations far below the critical micelle concentration, named critical aggregation concentration (cac), which was determined for both surfactants in the presence of SiPy+Cl− (cac Triton X = 2.4 × 10−6 and SDS = 8.2 × 10−7 mol L−1). The coexistence of mixed and pure micelles containing only Triton X and SDS also occurs in higher surfactant concentrations. The implication of these aggregates adsorption on the surface was analyzed in thin films by using the LbL technique. Multilayered films were obtained in presence of surfactants, (T-SiPy/NiTsPc) n or (S-SiPy/NiTsPc) n to compare with LbL films in absence of surfactant (SiPy/NiTsPc) n , and these films were characterized by UV–Vis, FTIR, and Raman spectroscopies to analyze the molecular interactions and to investigate the presence of specific interactions between the polyelectrolytes. The formation of LbL film in the architectures (T-SiPy/NiTsPc) n or (S-SiPy/NiTsPc) n is more efficient in relation to (SiPy/NiTsPc) n LbL films since the presence of the surfactants causes a greater amount of material to be deposited on each bilayer formed. The results of UV–Vis indicate that the film in the presence of SDS has a higher amount of material added to each bilayer. The electrochemical studies of (S-SiPy/NiTsPc)3 film show that the charge transfer resistance is lower than the one observed for the other architectures. Thus, the characteristic hopping electron effect of LbL film may be responsible for lower capacitance and lower resistance of the films. When the surfactant SDS is present, a higher oxidation peak current of dopamine is seen.

Effect of Foam on Liquid Phase Mobility in Porous Media

We investigate the validity of the assumption that foam in porous media reduces the mobility of gas phase only and does not impact the liquid-phase mobility. The foam is generated by simultaneous injection of nitrogen gas and a surfactant solution into sandstone cores and its strength is varied by changing surfactant type and concentration. We find, indeed, that the effect of foam on liquid-phase mobility is not pronounced and can be ignored. Our new experimental results and analyses resolve apparent discrepancies in the literature. Previously, some researchers erroneously applied relative permeability relationships measured at small to moderate capillary numbers to foam floods at large capillary number. Our results indicate that the water relative permeability in the absence of surfactant should be measured with the capillary pressure ranging up to values reached during the foam floods. This requires conducting a steady-state gas/water core flood with capillary numbers similar to that of foam floods or measuring the water relative-permeability curve using a centrifuge.

Surfactant Effects on Tautomeric and Microscopic Equilibria of Tryptophan: Experimental and Theoretical Studies

Surfactant molecules are used as interesting tools to study the structure, function and stability of proteins. Protonation states of amino acids may be changed in the presence of surfactants. In this work, using experimental observations and molecular dynamic simulation, the effects of sodium dodecyl sulfate on the acid dissociation constants of tryptophan was examined. The acid–base equilibrium of tryptophan molecules was examined in the aqueous solution and in the presence of different concentrations of SDS. Different concentrations of SDS have diverse effects on the values of pKa1. However, the effect of SDS on pKa2 is similar in all concentration ranges. Furthermore, the microconstants related to the same equilibria (k11, k22, k12, and k21) have different values in the presence and absence of SDS. These results show the different protonation states of tryptophan molecules in the presence and absence of surfactant. Molecular dynamics simulation showed that in the absence of SDS, tryptophan molecules form molecular aggregates similar to the result of stacking. But in the presence of SDS, stacking between tryptophan molecules is disrupted by hydrophobic and hydrogen bonding interactions of surfactant.

A new nanocomposite superionic system (CdHgI4/HgI2): Synthesis, characterization and experimental investigation

In this paper, we report a new and convenient synthetic method based on a reaction in an aqueous system, which can produce a new nanocomposite superionic system (CdHgI4/HgI2) at 70°C for 20min. It is the first time that these nanocomposites are synthesized. In this work, we have chosen lithium iodide, cadmium and mercury acetate as starting reagents. First, an aqueous solution of cadmium acetate, surfactant and lithium iodide is obtained. Second, an aqueous solution of mercury acetate and lithium iodide is prepared. Then obtained solution is added to the first solution. The effects of the surfactant and mole ratio of Cd:Hg have been optimized to achieve the best products on morphology and purity. When the molar ratio of Cd:Hg is 1:1, in the absence of surfactant also in the presence of CTAB and Triplex, pure aggregated nanostructures are formed. The nanocomposites are characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and cyclic voltammetry (CV). The electrical conductivity measurement carries out at frequencies of 100Hz, 1000Hz, 10kHz and 100kHz in the temperature range 70–140°C. Results show that the best morphology and purity have been achieved in the absence of surfactant, in 1:1 ratio of precursors.

Determination of Iron, Copper, Zinc, Aluminum, and Chromium in Biodiesel by Flame Atomic Absorption Spectrometry Using a Microemulsion Preparation Method

This work proposes a flame atomic absorption spectrometry (FAAS) method for Fe, Cu, Zn, Al, and Cr determination in biodiesel using water in oil (w/o) microemulsion (ME) as a sample preparation method. A less toxic solvent (n-propanol), instead of those used in the standard method (ABNT NBR 15556), the absence of surfactant, and calibration using inorganic reference standards were investigated. A ternary phase diagram of biodiesel as oil, water, nitric acid, and n-propanol showed a single-phase ME region. The composition of ME adopted for analysis was 1.7 g of biodiesel and 1.1 mL of 1.4 mol L–1 HNO3, completed with n-propanol to 10 mL volume. Linear calibration graphs with R > 0.99 were obtained using ME prepared with oleic acid and inorganic standards. Analytes were stable for at least 3 days both in sample and in metallic standards MEs. The limits of detection obtained were 0.3, 0.1, 0.07, 1.7, and 1.0 mg kg–1 for Fe, Cu, Zn, Al, and Cr, respectively. These limits of detection were lower than those obt...

Adsorption of silica colloids onto like-charged silica surfaces of different roughness

Particle adsorption was explored in a model optical polishing system, consisting of silica colloids and like-charged silica surfaces. The adsorption was monitored in situ under various suspension conditions, in the absence of surfactants or organic modifiers, using a quartz crystal microbalance with dissipation monitoring (QCM-D). Changes in surface coverage with particle concentration, particle size, pH, ionic strength and ionic composition were quantified by QCM-D and further characterized ex situ by atomic force microscopy (AFM). A Monte Carlo model was used to describe the kinetics of particle deposition and provide insights on scaling with particle concentration. Transitions from near-zero adsorption to measurable adsorption were compared with equilibrium predictions made using the Deraguin-Verwey-Landau-Overbeek (DLVO) theory. In addition, the impact of silica surface roughness on the propensity for particle adsorption was studied on various spatial scale lengths by intentionally roughening the QCM sensor surface using polishing methods. It was found that a change in silica surface roughness at the AFM scale from 1.3nm root-mean-square (rms) to 2.7nmrms resulted in an increase in silica particle adsorption of 3-fold for 50-nm diameter particles and 1.3-fold for 100-nm diameter particles—far exceeding adsorption observed by altering suspension conditions alone, potentially because roughness at the proper scale reduces the total separation distance between particle and surface.

Influence of Composite Nano Coating on Ternary Sulphate Co-deposition: Corrosion and Surface Characterization

In this study, composite Zn-ZnO-MgO have been produced from a sulphate bath in the presence of dispersible MgO nano composite on mild steel substrate in the absence of surfactant. The resulting fabricated coating shown that the amount of MgO embedded in the coating is dependent not only on the time of deposition but also the incorporated particulate and the applied current density. The influence of the particulate from 8-16 wt% on the ternary series was extensively investigated on the coating efficiencies and coating texture. The structural changes of the co-deposited alloys were investigated by scanning electron microscope coupled with energy dispersive spectroscopy (SEM-EDS). The corrosion characteristics properties in 3.65% NaCl medium were studied using linear potentiodynamic polarization route and characterized by high resolution optical microscope. Results show the deposition of MgO particulate contribute immensely to the corrosion propagation resistance of the Zn-ZnO-MgO coating. It was also established that the addition of the dispersible composite significantly influence the coating texture and efficiency.

Influences of Micelle Formation and Added Salts on the Hydrolysis Reaction Rate of p‐Nitrophenyl Benzoate in Aqueous Buffered Media

ABSTRACTThe hydrolysis reaction rate of p‐nitrophenyl benzoate (p‐NPB) has been examined in aqueous buffer media of pH 9.18, containing surfactants, cetyltrimethylammonium bromide (CTAB) and chloride (CTAC), or sodium dodecyl sulfate (SDS) at 35°C. Although the rate constant [log (k/s−1)] of p‐NPB hydrolysis has once decreased slightly below the critical micelle concentration (CMC) value for CTAB and CTAC, it has begun to increase drastically with micellar formation. With increasing concentrations larger than the CMC value, the log (k/s−1) value has reached the optimal value, i.e., a 140‐ and 200‐fold rate acceleration for CTAB and CTAC, respectively, compared to that without a surfactant. Whereas the anionic surfactant, SDS, has caused only a gradual rate deceleration in the whole concentration range (up to 0.03 mol dm−3). Increases in pH of the buffer have resulted in increases of the hydrolysis rate. In the CTAB micellar solution, the remarkably enhanced rate has been retarded significantly by the addition of only 0.10 mol dm−3 bromide salts. The effects of rate retardation caused by the added salts follows in the order of NaBr > Me4NBr > Et4NBr > Pr4NBr > n‐Bu4NBr. In the absence of surfactant, however, the addition of the bromide salts has accelerated the hydrolysis rate, except for the metallic salt of NaBr, with the order of Me4NBr < Et4NBr < Pr4NBr < n‐Bu4NBr. In the CTAC micellar solution, similar rate retardation effects have been observed in the presence of chloride salts (NaCl, Et4NCl, and n‐Bu4NCl). The effects of added salts have been interpreted from the viewpoints of the changes in activity of the OH− ion and/or the nucleophilicities of the anions from the added salts.