Layer-by-layer electrodeposition of copper in the presence of o-phenanthroline, caused by a new type of hidden NDR oscillation with the effective electrode surface area as the key variable

Electrochemical deposition of copper (Cu) from aqueous acidic Cu2+ solutions with o-phenanthroline (o-phen) shows both potential and current oscillations, together with a (partially hidden) N-shaped negative differential resistance (N-NDR), indicating that the oscillations are classified into hidden N-NDR (or HN-NDR) oscillations. The color and the surface morphology of Cu deposits oscillate in synchronization with the potential and current oscillations. Microscopic inspection has shown that dense round Cu leaflets, which look gray, grow in the positive side of the potential oscillation or in the high-current state of the current oscillation, whereas thin Cu leaflets, which look black, grow in the opposite-side stages of the potential and current oscillations, thus finally resulting in a layered Cu deposit with the layer thickness of about 5 microm. The appearance of the NDR is explained to be due to adsorption of the reduced form of a [Cu(II)(o-phen)2]2+ complex, which suppresses the Cu electrodeposition. The increase in the effective electrode surface area by growth of thin Cu leaflets, on the other hand, causes a current increase that can hide the NDR. This NDR-hiding mechanism is of a new type and the present oscillation is regarded as a new-type of HN-NDR oscillator.     

Spontaneous periodic pulsation of contact line in oil/water system--frequency control with divalent cations and applied voltage

Periodic oscillatory change of hydrophilicity (or hydrophobicity) of a glass surface was studied. A glass capillary was immersed normally at an oil/water interface. The water phase contained the cationic surfactant trimethyloctadecylammoniumchloride, and the oil phase contained bis(2ethylhexyl) phosphate. Adsorption of the surfactant molecules and their desorption via anionic chemicals dissolved in the oil generated a gradual wetting by the water, followed by a rapid wetting by oil. The three phase contact line exhibited a pulse-like motion that continued, at least for a few minutes. The frequency depended on the cation species dissolved in water and the applied voltage across the oil/water interface. Four kinds of cations, Mg(2+), Ca(2+), Sr(2+) and Ba(2+) were used. While the frequency order was Ba(2+)>Sr(2+)>Mg(2+), the Ca(2+)-containing interface did not show any motion irrespective of the applied voltage. There was a threshold voltage and concentration of anionic chemical that was necessary for the onset of this motion. The pulsation mechanism and its ion selectivity are also discussed. This interfacial motion was a typical nonlinear oscillation with an ion-selective nature. In this regard, this interfacial motion had biomimetic characteristics.     

Dispersion stability of a ceramic glaze achieved through ionic surfactant adsorption

The adsorption of cetylpyridinium chloride (CPC) and sodium dodecylbenzenesulfonate (SDBS) onto a ceramic glaze mixture composed of limestone, feldspar, quartz, and kaolin has been investigated. Both adsorption isotherms and the average particle zeta potential have been studied in order to understand the suspension stability as a function of pH, ionic strength, and surfactant concentration. The adsorption of small amounts of cationic CPC onto the primarily negatively charged surfaces of the particles at pH 7 and 9 results in strong attraction and flocculation due to hydrophobic interactions. At higher surfactant concentrations a zeta potential of more than +60 mV results from the bilayered adsorbed surfactant, providing stability at salt concentrations < or = 0.01 M. At 0.1 M salt poor stability results despite substantial zeta potential values. Three mechanisms for SDBS adsorption have been identified. When anionic SDBS monomers either adsorb by electrostatic interactions with the few positive surface sites at high pH or adsorb onto like charged negative surface sites due to dispersion or hydrophobic interactions, the magnitude of the negative zeta potential increases slightly. At pH 9 this increase is enough to promote stability with an average zeta potential of more than -55 mV, whereas at pH 7 the zeta potential is lower at about -45 mV. The stability of suspensions at pH 7 is additionally due to steric repulsion caused by the adsorption of thick layers of neutrally charged Ca(DBS)2 complexes created when the surfactant interacts with dissolved calcium ions from the calcium carbonate component.     

Use of surfactants to remove water-based inks from plastic film: effect of calcium ion concentration and length of surfactant hydrophobe

Effective plastic film deinking could permit the reuse of recycled polymer to produce clear film, reduce solid waste for landfills, reduce raw material demand for polymer production, and aid process economics. In this study, the deinking of a commercial polyethylene film printed with water-based ink was studied using surfactants in the presence of hardness ions (calcium ions) at various pH levels. The electrostatic properties of ink particles in a washing bath were also investigated. Synthetic anionic surfactant or fatty acid soap in the presence of calcium ions at alkaline pH levels was found to be nearly as effective at deinking as cationic, nonionic, or amphoteric surfactants alone. However, adding calcium ions decreases the deinking effectiveness of cationic, nonionic, and amphoteric surfactants. Increasing the length of the ionic surfactant hydrophobe enhances deinking. Zeta potential measurements showed that water-based ink particles in water reach the point of zero charge (PZC) at a pH of about 3.6, above which ink particles are negatively charged, so cationic surfactant tends to adsorb better on the ink than anionic surfactant above the PZC in the absence of calcium. As the cationic surfactant concentration is varied between 0.005 and 25 mM, the zeta potential of the ink particles reverses from negative to positive owing to adsorption of cationic surfactant. For anionic surfactants, added calcium probably forms a bridge between the negatively charged ink and the negatively charged surfactant head groups, which synergizes adsorption of the surfactant and aids deinking. In contrast, calcium competes for adsorption sites with cationic and nonionic surfactants, which inhibits deinking. All the surfactants studied here disperse ink particles effectively in the washing bath above pH 3 except for the ethoxylated amine surfactant.     

Gemini表面活性剂(12-6-12)和DNA的相互作用

应用紫外光谱、荧光探针、zeta 电位、动态光散射和凝胶电泳等方法探讨了阳离子gemini 表面活性剂C₁₂H₂₅N⁺(CH₃)₂―(CH₂)₆―(CH₃)₂N⁺C₁₂H₂₅·2Br^-(12-6-12)与DNA之间的相互作用. 研究结果表明, 与传统表面活性剂相比, 偶联表面活性剂特殊的分子结构使其与DNA的作用更强烈. DNA引导表面活性剂在其链周围形成类胶束结构, 开始形成类胶束时对应的表面活性剂临界聚集浓度(CAC)比纯表面活性剂临界胶束浓度(CMC)低两个数量级. CAC与DNA的浓度无关, 而与表面活性剂之间的疏水作用以及表面活性剂与DNA之间的静电吸引作用密切相关. Zeta 电位和凝胶电泳结果显示了DNA链所带负电荷逐渐被阳离子表面活性剂中和的过程. 借助原子力显微镜(AFM)成功观察到了松散的线团状DNA, 球状体随机地分散在DNA链上形成类似于串珠的结构、尺寸较大的球形复合物以及其由于吸附多余的表面活性剂重新带正电而被溶解得到的较小DNA/12-6-12聚集体. 圆二色(CD)光谱结果显示, 12-6-12可以诱导DNA的构象发生改变.     

Unique role of ionic liquid [bmin][BF4] during curcumin-surfactant association and micellization of cationic, anionic and non-ionic surfactant solutions

Hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroburate, modified the properties of aqueous surfactant solutions associated with curcumin. Because of potential pharmaceutical applications as an antioxidant, anti-inflammatory and anti-carcinogenic agent, curcumin has received ample attention as potential drug. The interaction of curcumin with various charged aqueous surfactant solutions showed it exists in deprotonated enol form in surfactant solutions. The nitro and hydroxyl groups of o-nitrophenol interact with the carbonyl and hydroxyl groups of the enol form of curcumin by forming ground state complex through hydrogen bonds and offered interesting information about the nature of the interactions between the aqueous surfactant solutions and curcumin depending on charge of head group of the surfactant. IL[bmin][BF4] encouraged early formation of micelle in case of cationic and anionic aqueous surfactant solutions, but slightly prolonged micelle formation in the case of neutral aqueous surfactant solution. However, for curcumin IL [bmin][BF4] favored strong association (7-fold increase) with neutral surfactant solution, marginally supported association with anionic surfactant solution and discouraged (～2-fold decrease) association with cationic surfactant solution.     

Forces between glass surfaces in mixed cationic-zwitterionic surfactant systems

We report atomic force microscopy (AFM) measurements of the forces between borosilicate glass solids in aqueous mixtures of cationic and zwitterionic surfactants. These forces are used to determine the adsorption of the surfactant as a function of the separation between the interfaces (proximal adsorption) through the application of a Maxwell relation. In the absence of cationic surfactant, the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) undergoes little adsorption to glass at concentrations up to about 2/3 critical micelle concentration (cmc). In addition, DDAPS does not have much effect on the forces over the same concentration range. In contrast, the cationic surfactant dodecylpyridinium chloride (DPC) does adsorb to glass and does affect the force between glass surfaces at concentrations much lower than the cmc. In the presence of a small amount of DPC (0.05 mM = cmc/300), the net force between the glass surfaces is quite sensitive to the solution concentration of DDAPS. A model-independent thermodynamic argument is used to show that the surface excess of DDAPS depends on the separation between the glass interfaces when the cationic surfactant is present and that the surface excess of the cationic surfactant is more sensitive to interfacial separation in the presence of the zwitterionic surfactant. The change in adsorption of the zwitterionic surfactant is explained in terms of an intermolecular coupling between the long-range electrostatic force acting on the cationic surfactant and the short-range hydrophobic interaction between the alkyl chains on the cationic and zwitterionic surfactants. The adsorptions of cationic and zwitterionic surfactants in mixtures were measured independently and simultaneously by attenuated total internal reflection infrared spectroscopy (ATR-IR). The adsorption of the zwitterionic surfactant is enhanced by the presence of a small amount of cationic surfactant.     

Effect of Surfactants on the Formation,Morphology, and Surface Property of Synthesized SiO2 Nanoparticles

Abstract

This study investigated the effect of cationic, anionic (saturated and unsaturated), and nonionic surfactants on the formation, morphology, and surface properties of silica nanoparticles synthesized by the ammonium‐catalyzed hydrolysis of tetraethoxysilane in alcoholic media. Results indicate that at a relatively low surfactant concentration (1 × 10^?3–1 × 10^?6 M), cationic surfactants significantly affected the growth of silica particles as measured by dynamic light scattering and transmission electron microscopic analyses. In contrast, the anionic and nonionic surfactants showed relatively minor effects in the low concentration range. The magnitude of negative zeta potential was reduced for silica colloids that were synthesized in the presence of cationic surfactant because of charge neutralization. The presence of anionic surfactants only slightly increased the negative zeta potential while the nonionic surfactant showed no obvious effects. At high surfactant concentrations (>1 × 10^?3 M), cationic and anionic surfactants both induced colloid aggregation, while the nonionic surfactant showed no effect on particle size. Raman spectroscopic analysis suggests that molecules of cationic surfactants adsorb on silica surfaces via head groups, aided by favorable electrostatic attraction, while molecules of anionic and nonionic surfactants adsorb via their hydrophobic tails.     

Wormlike micelles in poly(oxyethylene) surfactant solution: Growth control through hydrophilic-group size variation

Rheological responses of colloidal gels formed from fumed silica suspensions in aqueous KOH solution at pH 11 by the addition of cationic surfactants, such as dodecyltrimethylammonium chloride (C12 TAC) and hexadodecyltrimethylammonium chloride (C16 TAC) have been investigated as functions of silica and surfactant concentrations. Stable and aggregated fumed silica suspensions with negative charges cause gelling by adding the cationic surfactants through electrical neutralization of their micelles. The resulting critical strain and storage modulus of the gelled silica suspension increase with an increase in the surfactant concentration, irrespective of the cationic surfactant. This means that the higher the surfactant concentration is, the more effective the electrical neutralization interaction through the micelle of the cationic surfactant is. Moreover, the resulting gels can be classified into the strong-link gel and the weak-link one in the presence of C12 TAC and C16 TAC, respectively, from a comparison of the silica volume fraction dependences of critical strain and storage modulus with the fractal gel model.     

A Synergistic Effect of Select Organotin Compounds and Ionic Surfactants on Liposome Membranes

Organometallic compounds and surfactants constitute a potential threat to the environment. For that reason we have embarked on a study of their joint action on membranes. Model lecithin liposome membranes were modified with the cationic surfactant trimethyldodecylammonium bromide or the anionic surfactant sodium dodecylsulfonate, and the effect of tripropyltin chloride on the process of calcium (Ca²⁺) and praseodymium (Pr³⁺) desorption from the liposome membrane was studied. Kinetic constants for the process of Ca²⁺ ion desorption from lecithin liposome membranes were determined using the radiotracer method. The percentage of Pr³⁺ ion desorption from liposome membranes was measured by the ¹H NMR method. Trimethyltin, triethyltin and tripropyltin alone caused increased Ca²⁺ and Pr³⁺ desorption from liposome membranes with increasing concentration of the compounds and alkyl chain length. For both the processes studied, a cationic surfactant brought about a lower effectiveness of tripropyltin and an anionic surfactant resulted in a higher effectiveness. The effect observed can be explained by changes in the surface charge of the membrane, induced by the surfactant modifiers and by the concomitant change in the partition coefficient of the organotin. The results obtained indicate a protective or harmful joint action of the surfactants used with tripropyltin on membranes. © 1997 John Wiley & Sons, Ltd.     

Effect of polyelectrolytes and polyelectrolyte mixtures on the electrokinetic potential of dispersed particles. 1. Electrokinetic potential of polystyrene particles in solutions of surfactants, polyelectrolytes and their mixtures

The effect of cationic and anionic surfactants, as well as cationic and anionic polyelectrolytes (PE), their binary mixtures on the electrokinetic potential of monodisperse carboxylated polystyrene (PS) particles as a function of the reagents dose, pH, the charge density (CD) of polymers, the surfactant/PE and binary PE mixture composition, and sequence of components addition to the suspension has been studied. It has been shown that addition of increasing amount of anionic surfactant/polyelectrolytes increases the absolute value of the negative zeta-potential of PS particles; this increase is stronger the CD of the PE and pH of the system are higher. Adsorption of cationic surfactant/polyelectrolytes leads to a significant decrease in the negative ζ-potential and to overcharging the particles; changes in the ζ-potential are more pronounced for PE samples with higher CD and for suspensions with lower pH values. In mixtures of cationic and anionic PE, in a wide range of mixture composition, the ζ-potential of particles is determined by the adsorbed amount of the anionic polymer independently of the CD of PEs and the sequence of addition of the mixture components. The isoelectric point of the surface is reached at the adsorbed amount of positive charges of PE that is approximately equal to the surface CD of particles. The laws observed were explained by features of macromolecules conformation in adsorbed mixed PE layers. Considerations about the role of coulombic and non-coulombic forces in the mechanism of anionic/cationic PE adsorption are presented.     

Enhancement of the fluorescence of the zinc-morin complex by a non-ionic surfactant

A method is described for the fluorimetric determination of zinc, based on formation of a zinc-morin complex in the presence of a non-ionic surfactant. The complex has practically no fluorescence in the absence of surfactant, but the addition of Genapol PF-20 (non-ionic surfactant, ethylene oxide-propylene oxide condensate) makes possible the fluorimetric determination of low concentrations of zinc as it enhances the fluorescence of the complex about 75-fold. Maximum fluorescence is produced at pH 4.7 +/- 0.2 (acetic acid-acetate buffer), with 1.5% surfactant and 0.009% morin. The fluorescence is excited at 433 nm and measured at 503 nm. The calibration graph is linear up to 150 ng/ml zinc concentration and the detection limit is 3 ng/ml. The relative standard deviation (11 replicates) is 2.4% for zinc at 20 ng/ml concentration and 1.7% for 100 ng/ml. Of 29 ions studied, Al(3+), Be(2+), Zr(4+) and Cd(2+) strongly increase the fluorescence of the system, and Fe(3+), Ni(2+), Cu(2+), Ti(IV) and Co(2+) decrease the fluorescence signal.     

Negative differential resistance in oxidized zigzag graphene nanoribbons

A theoretical study of zigzag graphene nanoribbons (ZGNRs) with an epoxy-pair chain (ZGO) is performed. The electronic transport properties are mainly evaluated by non-equilibrium Green's functions using the TRANSIESTA package. The results indicate that the graphene oxide can have a negative differential resistance (NDR) phenomenon, supported by bias-dependent transmission curves of different spin orientations. Applying non-zero bias voltages makes the density of states (DOS) of the right electrodes shift down. Due to an energy gap between the LUMO and LUMO+1 in ZGOs, with a certain bias, the conduction band of the right electrode cannot match the LUMO of the scattering region, then NDR occurs. With a larger bias, NDR ends when the second conduction band of the right electrode's DOS covers the LUMO of the scattering region. Since most of proposed ZGO systems possess such a gap between the LUMO and LUMO+1, NDR can be widely observed and this discovery may provide great potential applications in NDR-based nanoelectronics by using modified graphene materials.     

Charge reversal at the air/water interface as inferred from the thickness of foam films

Experiments are reported with foam films from aqueous solutions with increasing concentration of a cationic surfactant. A correlation is established between the foam film thickness and the possible variation of diffuse electric layer potential at the air/water interface from a negative value in absence of surfactant to positive values at higher surfactant concentrations. It is concluded that a charge reversal at the air/water interface is expected to occur under increasing concentration of cationic surfactants in aqueous solutions.     

Complexation of DNA with cationic gemini surfactant in aqueous solution

Interactions between DNA and the cationic gemini surfactant trimethylene-1,3-bis(dodecyldimethylammonium bromide) (12-3-12) in aqueous solution have been investigated by UV-vis transmittance, zeta potential, and fluorescence emission spectrum. Complexes of DNA and gemini surfactant are observed in which the negative charges of DNA are neutralized by cationic surfactants effectively. The DNA-induced micelle-like structure of the surfactant due to the electrostatic and hydrophobic interactions is determined by the fluorescence spectrum of pyrene. It is found that the critical aggregation concentration (CAC) for DNA/12-3-12 complexes depends little on the addition of sodium bromide (NaBr) because of the counterbalance salt effect. However, at high surfactant concentration, NaBr facilitates the formation of larger DNA/surfactant aggregates. Displacement of ethidium bromide (EB) by surfactant evidently illustrates the strong cooperative binding between surfactant and DNA. In contrast to that in the absence of surfactant, the added NaBr at high surfactant concentration influences not only the binding of surfactant with DNA, but also the stability of DNA/EB complex.     

Synthesis, characterization, and interfacial properties of an oligomeric, cationic fluorooxetane

The synthesis and characterization of a cationic oligo(fluorooxetane) surfactant with pendant -C4F9 groups are reported. Molecular area demand at saturation was determined to be 55.6 +/- 0.3 angstroms2/molecule and characteristic of an oligomer. The adsorption of the cationic oligo(fluorooxetane) to the air-water interface appears to be diffusion-limited, and dilational rheological properties of the adsorbed molecules are representative of a "soluble" monolayer. Adsorption dynamics have been measured yielding diffusion coefficients that are dependent on concentration and in the 10(-7)-10(-8) cm2/s range. Complex moduli from dilational interfacial rheological measurements as a function of oscillation frequency were well fitted to the Lucassen-van den Tempel equation, providing an estimate of the Gibbs elasticity. The combination of the oligomeric nature of the fluorosurfactant, short perfluoroalkyl chain and its interfacial properties suggests that this synthetic approach is an attractive route to the development of fluorinated surfactants that avoid the environmental concerns of small-molecule, long perfluoroalkyl-chain surfactants.     

Crystal structure of benzyl triphenyl phosphonium chlorometallate: Some surface and biological properties of their metallosurfactant derivatives

The crystal structures of benzyl triphenyl phosphonium tri-chloro cupprate (1) and tetra-chloroferrate (2) have been determined by X-ray crystallography. The structures contain completely isolated elongated tetrahedral [CuCl₃]^? as dimmers with two bridging and four terminal chlorines (1), and tetrahedral [FeCl₄]^? (2). In designing a metal containing surfactant system, salts (1) and (2) were refluxed with dodecyl amine to form the corresponding metallosurfactants (1a) and (2a) or to hexadecyl pyridinium chloride to form the corresponding cationic metallosurfactants (1b) and (2b), respectively. The critical micelle concentration (CMC) values of these surfactant metal complexes in aqueous solution were recorded from surface tension measurements. They showed antibacterial activity against the growth of Gram positive and Gram negative bacteria.     

Thermodynamics of micellization of multiheaded single-chain cationic surfactants

The energetics of micelle formation of three single-chain cationic surfactants bearing single (h = 1), double (h = 2), and triple (h = 3) trimethylammonium [(+)N(CH(3))(3)] headgroups have been investigated by microcalorimetry. The results were compared with the microcalorimetric data obtained from well-known cationic surfactant, cetyl trimethylammonium bromide (CTAB), bearing a single chain and single headgroup. The critical micellar concentrations (cmc's) and the degrees of counterion dissociation (alpha) of micelles of these surfactants were also determined by conductometry. The cmc and the alpha values increased with the increase in the number of headgroups of the surfactant. The relationship between the cmc of the surfactant in solution and its free energy of micellization (DeltaG(m)) was derived for each surfactant. Exothermic enthalpies of micellization (DeltaH(m)) and positive entropies of micellization (DeltaS(m)) were observed for all the surfactants. Negative DeltaH(m) values increased from CTAB to h = 1 to h = 2 and decreased for h = 3 whereas DeltaS(m) values decreased with increase in the number of headgroups. The DeltaG(m) values progressively became less negative with the increase in the number of headgroups. This implies that micelle formation becomes progressively less favorable as more headgroups are incorporated in the surfactant. From the steady-state fluorescence measurements using pyrene as a probe, the micropolarities sensed by the probe inside various micelles were determined. These studies suggest that the micelles are more hydrated with multiheaded surfactants and the micropolarity of micelles increases with the increase in the number of headgroups.     

Observations of the effect of anionic, cationic, neutral, and zwitterionic surfactants on the Belousov-Zhabotinsky reaction

In this paper we report the experimental observations of the effects of various surfactants on the oscillations of the ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction. The oscillations are followed by observing the change in absorbance at 510 nm due to ferroin in a well-stirred closed BZ reacting system. We have used sodium dodecyl sulfate (SDS) as the anionic surfactant, cetyl trimethylammonium bromide (CTAB) as the cationic surfactant, Triton X-100 as the neutral surfactant, and 3-[(3-cholamidopropyl)dimethylammonio)]-1-propanesulfonate (CHAPS) as the zwitterionic surfactant. In general, we observed that there is a change in the oscillation behavior in the presence of each of these surfactants above their critical micellar concentrations. For different surfactants, the time-dependent evolution of the oscillations is found to be characteristic of the surfactant. The results of our study suggest that the evolution of oscillations is most regular in the presence of micelles of SDS.     

Electrokinetic potential of multilayer carbon nanotubes in aqueous solutions of electrolytes and surfactants

The effect of electrolytes with single-, double- and triple-charged counterions, as well as cationic (cetyltrimethylammonium bromide) and anionic (sodium dodecyl sulfate) surfactants, on the electrokinetic potential of multiwall carbon nanotubes prepared via catalytic pyrolysis of propylene in a gas phase according to the CCVD technology has been studied. It has been shown that the influence of different electrolytes on the electrophoretic mobility of the nanotubes does not differ essentially from their effect on the behavior of well-studied inorganic dispersed particles; i.e., the dependence of the absolute values of the ζ-potential on the concentration of a 1: 1 electrolyte passes through a maximum and the introduction of double-charged counterions dramatically reduces the ζ-potential, while the addition of triple-charged cations and a cationic surfactant causes charge reversal of the nanotube surface. The adsorption of sodium dodecyl sulfate in a neutral medium increases the negative ζ values; this effect evens out in the presence of an alkali due to a rise in the electrostatic repulsion between surfactant anions and nanotube surface, which bears a high negative charge resulting from the dissociation of surface functional groups.