Redox-active Surfactant Research Articles

Interfacial properties and aggregates of novel redox-active surfactant to synthesize silver nanoparticles at the air/water interface

An anionic and amphiphilic molecule, AQua (AQ-NH-(CH2)10COOH; where AQ is anthraquinone), which has two stimuli responsive functional-groups, can form self-assembled interfacial aggregates at the air-water interface and, their morphologies can be controlled by changing the subphase conditions such as the pH of the subphase. These interfacial morphologies may be altered from planar structures to wormlike aggregates which is a very rare observation in the literature. Moreover, the unique functional groups of AQua give possibility to reduce metal cations and allow the formation of organic/inorganic nanocomposite structures at the interface. In this context, formation of silver nanoparticles (AgNPs) via AQua-based self-assembled structures at the interface was studied using Langmuir techniques. The kinetics of the reduction process as well as the effect of various parameters were systematically examined. This study demonstrates that interfacial configuration of the AQua molecule at the interface as well as its orientation has a vital role in the morphology of either organic or inorganic self-assemblies formed. The morphology may be adjusted and designed interfacial structures may be obtained. The interfacial properties of AQua, a novel material, may be used in a wide variety of fields such as biotechnology, medicine, energy and pharmaceuticals.

Effects of chain length on the size, stability, and electronic structure of redox-active organic–inorganic hybrid polyoxometalate micelles

Double-chain redox-active surfactants based on hybrid polyoxometalates show solvent-dependent assembly into nanoscale micellar architectures.

Ruthenocenyl Glycidyl Ether: A Ruthenium-Containing Epoxide for Anionic Polymerization

Ruthenocenyl glycidyl ether (rcGE) is a novel monomer for the anionic polymerization and copolymerization with ethylene oxide to water-soluble, thermo-, and redox-responsive organometallic poly(ethylene glycol)s (PEGs). The polymers exhibit adjustable molecular weights, comonomer ratios, and narrow molecular weight distributions (typically Mw/Mn < 1.2). Real-time 1H NMR copolymerization kinetics prove random incorporation of rcGE into the polyether backbone in analogy to its ferrocene analog. The rcGE-co-EO copolymers are water-soluble with a lower critical solution temperature, depending on the rcGE content. Terpolymerization of ferrocenyl glycidyl ether, ethylene oxide, and rcGE produces the first random PEG derivatives with multiple redox response. Ruthenocenyl glycidyl ether broadens the field of organometallics, especially ruthenium-containing polymers, and these copolymers might find applications in catalysis, as redox-active surfactants, or as staining reagents in electron microscopy.

Amphiphilic Ferrocene-Containing PEG Block Copolymers as Micellar Nanocarriers and Smart Surfactants.

An important and usually the only function of most surfactants in heterophase systems is stabilizing one phase in another, for example, droplets or particles in water. Surfactants with additional chemical or physical handles are promising in controlling the colloidal properties by external stimuli. The redox stimulus is an attractive feature; however, to date only a few ionic redox-responsive surfactants have been reported. Herein, the first nonionic and noncytotoxic ferrocene-containing block copolymers are prepared, carrying a hydrophilic poly(ethylene glycol) (PEG) chain and multiple ferrocenes in the hydrophobic segment. These amphiphiles were studied as redox-sensitive surfactants that destabilize particles as obtained in miniemulsion polymerization. Because of the nonionic nature of such PEG-based copolymers, they can stabilize nanoparticles even after the addition of ions, whereas particles stabilized with ionic surfactants would be destabilized by the addition of salt. The redox-active surfactants were prepared by the anionic ring-opening polymerization of ferrocenyl glycidyl ether, with PEG monomethyl ether as the macroinitiator. The resultant block copolymers with molecular weights (Mn) between 3600 and 8600 g mol-1 and narrow molecular weight distributions (Mw/Mn = 1.04-1.10) were investigated via 1H nuclear magnetic resonance and diffusion ordered spectroscopy, size exclusion chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Furthermore, the block copolymers were used as building blocks for redox-responsive micelles and as redox-responsive surfactants in radical polymerization in miniemulsion to stabilize model polystyrene nanoparticles. Oxidation of iron to the ferrocenium species converted the amphiphilic block copolymers into double hydrophilic macromolecules, which led to the destabilization of the nanoparticles. This destabilization of nanoparticle dispersions may be useful for the formation of coatings and the recovery of surfactants.

Micellar Aggregation Behavior and Electrochemically Reversible Solubilization of a Redox-Active Nonionic Surfactant

For the purpose of studying the potential of a novel nonionic switchable surfactant, 11-ferrocenylundecyl polyoxyethylene ether (FPEG), applied to surfactant-enhanced remediation (SER), the surface properties and micelle solubilization behavior of FPEG were investigated with different inorganic salts. With the addition of inorganic salts (NaCl and CaCl2), the critical micelle concentration (CMC) of FPEG dropped from 15 to 12 and 8 mg·L−1, respectively, due to the salting-out effect on the alkyl chain. Thermodynamic parameters based on the CMCs indicated that micelle formation was an entropy-driven process. Dynamic light scattering measurements verified that these inorganic salts can decrease the hydrodynamic diameters (D h) of the micelles. Solubilization experiments with three typical polycyclic aromatic hydrocarbons (PAHs) demonstrated that the system of FPEG with NaCl shows the highest solubilization ability, and the molar solubilization ratio and micelle–water partition coefficient (K m ) values follow the order pyrene > phenanthrene > acenaphthene. After oxidation, PAHs can be released from the micelles through breaking up of the micelles, and the cumulative release efficiency of pyrene, phenanthrene and acenaphthene are 31.2, 42.8 and 44.6 %; the order of release efficiency is opposite to that of the reduced form for solubilization abilities. All the results suggest that the ferrocene-containing, redox-active surfactant FPEG has the potential to be recycled in SER technology through electrochemistry approaches.

Electrochemically Reversible Solubilization of Polycyclic Aromatic Hydrocarbons by Mixed Micelles Composed of Redox-active Cationic Surfactant and Conventional Nonionic Surfactant

Reduplicate utilization of surfactants is a key factor for Surfactant-Enhanced Remediation (SER) technology to reduce its high operation costs. In order to achieve the reuse of surfactants, this study attempted to construct a novel reversible solubilization system for SER. Three typical polycyclic aromatic hydrocarbons (PAHs) pyrene, phenanthrene, and acenaphthene were controllably solubilized and released by the mixed micelles composed of redox-active cationic surfactant (11-Ferrocenylundecyl) trimethylammoniunm bromide (FTMA) and conventional nonionic surfactant Tween80. Solubilization of PAHs is assumed to be controlled by changing the redox states of FTMA. Cyclic voltammograms tests of FTMA showed the oxidation and reduction potential were 0.4570 and 0.4068 V, respectively, and the peak currents ratio of FTMA and FTMA+ was 1.26, verified that FTMA possesses electrochemically reversible property. In FTMA-Tween80 mixed solutions, CMC values demonstrated the nonideal interaction between the two surfactants and the interaction parameters (β) was -5.5296 when the mass ratio was FTMA:Tween80 = 2:8. Due to the synergistic solubilization effect, the apparent water solubilities of PAHs were significantly enhanced by the mixed surfactant, and they were much higher than those in single surfactant. After oxidation, more than 50% of the PAHs in mixed micelles could be released, the cumulative release efficiency of selected PAHs followed the order of pyrene > pherantherene > acenaphthene. Briefly, such results in this article provide a facile method to meliorate the SER technology.

Effect of a water structure modifier on the aqueous electrochemistry of supramolecular systems: Redox-active versus conventional surfactants

Aqueous electrochemistry of a redox-active nonionic surfactant, α-phenothiazinylhexyl-ω-hydroxy-oligo(ethylene oxide) (PCPEG) and phenothiazine (PT) and its derivative, PT-labeled poly(ethylene oxide) (PT-PEO) in aqueous solution of a conventional surfactant, cetyltrimethylammonium bromide (CTAB) above its critical micelle concentration (CMC) has been studied. Cyclic voltammetric results at a glassy carbon electrode in absence and presence of urea were compared to investigate the influence of water structure modification by urea on the micellization behavior of the surfactants. The addition of urea raises the CMC of CTAB by water structure breaking effect which influences the electrochemical behavior of PT and PT-PEO in aqueous solution. The electrochemical behavior on the other hand, does not exhibit any noticeable change with added urea in aqueous solution of PCPEG. This is due to the fact that water structure modification by urea is not sufficient to upset enhanced hydrophobic interaction due to aromatic π–π-stacking interaction from PT group to disrupt PCPEG micelles to monomeric PCPEG. The comparative and contrastive features of the effect of urea to influence micellization behavior and consequent electrochemical changes for conventional and redox-active surfactants have been discussed.

Mesomorphous Structure and Electrochemical Behavior of Polyelectrolyte-Ferrocenyl Surfactant Complexes

Redox-active polyelectrolyte-surfactant complexes (PSC) were prepared via the ionic self-assembly of sodium polyacrylate (PAAS) and ferrocenyl surfactant, n-alkyl (ferrocenylmethyl)ammonium bromide (Fcn, n = 8, 12, 16, where n is the carbon number of the alkyl chain), in solution. The obtained PAAS-Fcn complex exhibited crystalline and lamellar mesomorphous structure. Moreover, the ferrocenyl moieties formed H-aggregation in the solid complex as known from the blue shift in the ultraviolet-visible spectrum. Cyclic voltammogram (CV) measurements indicated that the reversibility of the electrode process became worse when the surfactant tail length increases because of the more ordered packing in the complex film formed by longer surfactant tails. The present results demonstrate that the electrochemical activity of the redox-active polyacrylate-ferrocenyl surfactant complex can be easily tuned by changing the surfactant tail length. Our work provides a simple and facile approach to the preparation of redox-active polymers with ordered mesomorphous structure by the ionic self-assembly.

Lateral Transport of Solutes in Microfluidic Channels Using Electrochemically Generated Gradients in Redox-Active Surfactants

We report principles for a continuous flow process that can separate solutes based on a driving force for selective transport that is generated by a lateral concentration gradient of a redox-active surfactant across a microfluidic channel. Microfluidic channels fabricated with gold electrodes lining each vertical wall were used to electrochemically generate concentration gradients of the redox-active surfactant 11-ferrocenylundecyl-trimethylammonium bromide (FTMA) in a direction perpendicular to the flow. The interactions of three solutes (a hydrophobic dye, 1-phenylazo-2-naphthylamine (yellow AB), an amphiphilic molecule, 2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (BODIPY C(5)-HPC), and an organic salt, 1-methylpyridinium-3-sulfonate (MPS)) with the lateral gradients in surfactant/micelle concentration were shown to drive the formation of solute-specific concentration gradients. Two distinct physical mechanisms were identified to lead to the solute concentration gradients: solubilization of solutes by micelles and differential adsorption of the solutes onto the walls of the microchannels in the presence of the surfactant concentration gradient. These two mechanisms were used to demonstrate delipidation of a mixture of BODIPY C(5)-HPC (lipid) and MPS and purification of BODIPY C(5)-HPC from a mixture of BODIPY C(5)-HPC and yellow AB. Overall, the results of this study demonstrate that lateral concentration gradients of redox-active surfactants formed within microfluidic channels can be used to transport solutes across the microfluidic channels in a solute-dependent manner. The approach employs electrical potentials (<1 V) that are sufficiently small to avoid electrolysis of water, can be performed in solutions having high ionic strength (>0.1M), and offers the basis of continuous processes for the purification or separation of solutes in microscale systems.

Electrochemical Generation of Gradients in Surfactant Concentration Across Microfluidic Channels

We report the generation and manipulation of spatial gradients in surfactant and micelle concentration across microfluidic channels by combining use of a redox-active surfactant with electrochemical methods. The approach is founded on the observation that 11-ferrocenylundecyltrimethylammonium bromide (FTMA) behaves as a surfactant in aqueous solution (e.g., self-assembles to form micelles at a critical concentration of 0.1 mM in aqueous 0.1 M Li(2)SO(4)) whereas oxidized FTMA remains dispersed in a monomeric state up to concentrations of at least 30 mM. By flowing aqueous FTMA solutions through microfluidic channels (width of 80 microm, depth of 72 microm, and length of 42 mm) and by applying potentials of 0 V (vs Ag|AgCl; cathode) and +0.3 V (vs Ag|AgCl; anode) to gold electrodes lining both side-walls of the microfluidic channels, we measured lateral gradients in concentration of oxidized FTMA and reduced FTMA to be generated across the microfluidic channels by splitting the exiting stream into four channels. These measurements revealed the lateral concentration profile of FTMA to be consistent with the presence of slowly diffusing micelles of FTMA in a spatially localized region near the cathode and monomeric FTMA only near the anode. The lateral concentration profiles of reduced and oxidized FTMA, and thus the patterning of micelles within the microfluidic channels, were manipulated via changes in the inlet FTMA concentration, potentials applied to the electrodes, and flow rate. These experimental measurements were compared to a simple model, which assumed fast electrode kinetics, lateral transport of FTMA by diffusion only (no migration), and local micelle-monomer equilibrium within the bulk solution. This comparison revealed qualitative but not quantitative agreement between model and experiment. Calculations of ionic conductivity and associated experimental measurements support the proposition that Ohmic resistance to the passage of current along the channel (between the working and the counter electrodes) contribute, in part, to the lack of quantitative agreement between the model and the measurements. The capability to generate and manipulate lateral concentration profiles of surfactants and micelles across microfluidic channels, as demonstrated by the results presented in this paper, offers the basis of new principles for continuous separation processes and microanalytical systems, and more broadly, new methods to generate gradients in concentration of analytes that interact with surfactants.

Effect of hydrophilic group on thin film formation using redox-active surfactants with an azobenzene group

Thin films of organic pigments were prepared at higher than pH 1 by the contact plating method using an anionic surfactant (AZNa, first figure of this article (part c) ( n = 4)) containing an azobenzene moiety. The effects of hydrophilic group of the surfactants on the rate of following reaction of the reduction product were studied by cyclic voltammetry. The positive shift of the reduction peak potential of AZNa compared to those of cationic and non-ionic surfactants was ascribed to higher rate of following reaction of reduction product due to the presence of the anionic hydrophilic group of the surfactant. The present investigation revealed that the anionic hydrophilic group accelerates the cleavage of the N N bond of the azobenzene group. This phenomenon enabled us to prepare the organic thin film at higher pH condition.

Methods for Generation of Spatial Gradients in Concentration of Monomeric Surfactants and Micelles in Microfluidic Systems

We report methods suitable for use in microfluidic systems that permit the generation and manipulation of spatial gradients in concentrations of monomeric surfactants and micelles within aqueous solutions. The methods involve the use of the redox-active surfactant, (11-ferrocenylundecyl)trimethyl-ammonium bromide (FTMA) and build from past studies that have established that FTMA exhibits a critical micelle concentration of 0.1 mM (in 0.1 M Li2SO4), whereas oxidized FTMA remains dispersed in a monomeric state up to concentrations of at least 30 mM. Following the application of potentials of 0 V (vs Ag|AgCl; cathode) and +0.3 V (vs Ag|AgCl; anode) to electrodes separated by distances of 25-116 microm, we measured steady state currents of equal magnitude to be passed at each electrode within 1-20 s of the onset of the application of the potentials. We used dynamic light scattering and surface tension measurements to determine that oxidized and reduced FTMA do not measurably interact in solution and thus interpret the steady state currents, measured as a function of the concentration of FTMA added to the system and distance between the electrodes, within the framework of a simple model that assumes fast electrode kinetics, local micelle-monomer equilibrium within the bulk solution, and transport by diffusion only (no migration). Comparison of experimental measurements and model predictions reveals good overall agreement, consistent with the presence of one-dimensional gradients in concentrations of monomeric FTMA and micelles of FTMA in solution between the electrodes. The nature of the gradients can be manipulated by the potentials applied to the electrodes and can be used to achieve spatially localized populations of micelles in the system.

Reversible Condensation of DNA Using a Redox-Active Surfactant

We report characterization of aqueous solutions of dilute Lambda phage DNA containing the redox-active surfactant (11-ferrocenylundecyl)trimethylammonium bromide (FTMA) as a function of the oxidation state of the FTMA. FTMA undergoes a reversible one-electron oxidation from a reduced state that forms micelles in aqueous solution to an oxidized state (containing the ferrocenium cation) that does not self-associate in solution. This investigation sought to test the hypothesis that FTMA can be used to achieve reversible control over the conformation of DNA-surfactant complexes in solution. Whereas DNA adopts extended coil conformations in aqueous solutions, our measurements revealed that addition of reduced FTMA (2-5 microM) to aqueous solutions of DNA (5 microM in nucleotide units) resulted in coexistence of extended coils and compact globules in solution. At higher concentrations of reduced FTMA (up to 30 microM), the DNA was present as compact globules only. In contrast, oxidized FTMA had no measurable effect on the conformation of DNA, allowing DNA to maintain an extended coil state up to a concentration of 75 microM oxidized FTMA. We further demonstrate that it is possible to chemically or electrochemically transform the oxidation state of FTMA in preformed complexes of FTMA and DNA, thus achieving in situ control over the conformations of the DNA in solution. These results provide guidance for the design of surfactant systems that permit active control of DNA-surfactant interactions.

Effect of particle size on the co-deposition of diamond with nickel in presence of a redox-active surfactant and mechanical property of the coatings

Particle reinforced Ni/diamond composite coatings containing various amount of the reinforcement (up to 57.6 vol.%) were prepared by the electroplating technique using a Watt's nickel bath in which the diamond particles were dispersed with the aid of a redox-active surfactant containing an azobenzene moiety. Five different sizes of diamond particles with the mean diameter ranging from 0.21 to 2.91 μm were used to investigate the effect of the particle size in their co-deposition with nickel under the influence of the above redox-active surfactant and the mechanical property especially the micro-hardness and the abrasion wear of the composite coatings reinforced with various amount of the diamond particles was studied. Among all, the smallest diamond particles exhibited the highest particle co-deposition of 57.6 vol.%. The micro-hardness and the wear resistance of this composite with the 57.6 vol.% diamond were about 4.5 and 14 times, respectively, than that of a nickel coating without any reinforcement.

Composite Plating Using an Electro-active Surfactant-A New Approach to Incorporate High Amount of Ceramic Particles into a Metallic Matrix-

The development of composite materials has been a subject of intensive interest for more than a century,but the concept of using two or more elemental materials combined to form a composite solid may have been employed ever since materials were first in used. In the case of particle dispersed metal matrix composite plating, the development can be traced back to 1960s. Nowadays, electrolytic deposition of particle dispersed metal matrix composite coating has already been a well-established technique. From its earliest development, the goal for a composite coating has been to achieve a combination of properties not achievable by any of the elemental materials acting alone. Thus, a composite coating could be prepared from constituents, which by themselves could not satisfy a particular design requirement. By combining various inert particles with metals, composite coatings with a number of improved properties could be prepared. For an example,nickel is one of the most widely used plating metals owing to its good chemical and mechanical properties. However, the strength of these properties is not enough to apply the nickel coatings in many engineering works. Therefore, further advancement on the nickel coatings is desirable, which can be achieved by incorporating the second phase especially the ceramic particles into the nickel matrix. Such particle reinforced nickel matrix composites generally exhibited the enhanced hardness, better anti-wear and anti-corrosion performance when compared to the pure metal and its alloys. These composite coatings are recently believed to be a possible candidate for the substitution of chromium coating. The properties of such composite coatings can be tailored by selecting a proper combination of metal and particles. For example, hard coatings can be achieved by co-depositing hard particles like diamond,c-BN,etc. with metals and their alloy especially Ni-P or Co-P alloy matrix. Similarly,friction less coatings can be achieved by co-depositing solid lubricating particles like MoS , PTFE,etc. However, in order to achieve the best performance of these composite coatings, the co-deposited particles must be uniformly dispersed in the matrix phase and the amount of these distributed phase must be more than 35 to 40vol.% for most of the engineering works. Although the composite plating of metal containing various inert particles has already been a well-established technique,the total amount of the particles that can be co-deposited with the metals even under the optimum conditions is often less than the amount of these particles required for many applications. For the last few years, the authors in this laboratory have been investigating various techniques to increase the particle content in a composite coating. One of the recently developed techniques is the application of the electrochemically redox-active surfactant containing an azobenzene unit in a composite plating bath, which enhanced the particle co-deposition dramatically. In this review, the authors will focus mainly about this technique and discuss specially about the synthesis,the interfacial electrochemistry and the application of the azobenzene surfactant in composite plating.

Electrochemical Control of the Interactions of Polymers and Redox-Active Surfactants

We report the characterization of aqueous solutions (0.1 M Li(2)SO(4)) of dilute ethyl(hydroxyethyl) cellulose (EHEC) mixed with the redox-active surfactant (11-ferrocenylundecyl)trimethylammonium bromide (FTMA) by measurements of clouding temperatures and dynamic light scattering. The investigation sought to test the hypothesis that FTMA, which forms micelles in aqueous solution in its reduced state but not in its oxidized state, would permit reversible control over the formation of polymer-surfactant complexes in solution. Our measurements revealed that low concentrations of reduced FTMA enhance aggregation, whereas high concentrations of reduced FTMA disperse polymer-surfactant aggregates. This behavior is qualitatively similar to both dodecyltrimethylammonium bromide and sodium dodecyl sulfate and reflects cooperative interactions between FTMA and EHEC. In contrast, oxidized FTMA was found not to promote EHEC aggregation at low concentrations of oxidized FTMA nor disperse EHEC aggregates at high concentrations. Measurements of dynamic light scattering revealed that the reduction of oxidized FTMA in solutions of EHEC containing 0.1-0.3 mmolal FTMA causes an increase in the sizes of polymer-surfactant aggregates of more than 1 order of magnitude. Our cloud point measurements also revealed that clouding can be induced isothermally via the electrochemical reduction of oxidized FTMA at room temperature at FTMA concentrations between 0.4 and 10 mmolal. In contrast, at concentrations of FTMA greater than 15 mmolal, the reduction of oxidized FTMA induces the clearing of EHEC solutions. We conclude that aggregation of EHEC in dilute solutions can be controlled by the manipulation of the oxidation state of FTMA.

Role of Desorption Kinetics in Determining Marangoni Flows Generated by Using Electrochemical Methods and Redox-Active Surfactants

We report quantitative measurements of Marangoni flows generated at the surfaces of aqueous solutions by using water-soluble redox-active surfactants in combination with electrochemical methods. These measurements are interpreted within the framework of a simple model that is based on lubrication theory and the proposition that the kinetics of the desorption of redox-active surfactants from the surfaces of aqueous solutions plays a central role in determining the strength of the Marangoni flow. The model predicts that the leading edge velocity of the Marangoni flow will decay exponentially with time and that the rate constant for the decay of the velocity can yield an estimate of the surfactant desorption rate constant. Good agreement between theory and experiments was found. By interpreting experimental measurements of electrochemically generated Marangoni flows within the framework of the model, we conclude that the desorption rate constant of the redox-active surfactant Fc(CH(2))(11)-N(+)(CH(3))(3)Br(-), where Fc is ferrocene, is 0.07 s(-)(1). We also conclude that the ionic strength of the aqueous solution has little effect on the desorption rate constant of the ferrocenyl surfactant.

Electrochemical properties and diffusion of a redox active surfactant incorporated in bicontinuous cubic and lamellar phase

The objective of this study was to investigate the electrochemical behaviour of the divalent redox active surfactant, N-cetyl- N′-methylviologen (CMV), in bicontinuous cubic and lamellar phases. The liquid crystalline phases were prepared from the system glycerolmonooleate (GMO)–water (and brine)–cationic surfactant. A comparison of the phase behaviour of GMO with the monovalent cetyltrimethylammonium bromide (CTAB) and the divalent CMV surfactant showed that the surfactants gave about the same effect at the same surface charge density. The electrochemical measurements were made with a mixture of CTAB and CMV as the surfactant. Cyclic voltammetry was used to study the electrochemistry of CMV incorporated in the cubic and lamellar phases that were spread on a gold electrode. The E 0-values in the cubic samples were more negative (−0.55 V versus SCE) than in the lamellar samples (−0.53 V versus SCE). This can be explained by the higher charge density in the lamellar phase. The diffusion coefficients were also measured in the cubic phase. The mass transport is slowed down about fifty times in the cubic phase compared to in the pure electrolyte. The concentration dependence on the diffusion coefficient was also investigated. No electron hopping could be observed, which suggest that diffusional movement of the redox probe is the main source of charge transport. By placing the samples on a conducting glass slide, spectroelectrochemical investigations were performed. In the lamellar phase strong dimerization was detected at high concentration of viologen, but much less in the cubic phase.

Co-deposition of B 4C particles and nickel under the influence of a redox-active surfactant and anti-wear property of the coatings

Composite plating of Ni/B 4C was carried out using cationic surfactants with and without an azobenzene group. The present investigation reveals that the azobenzene surfactant (AZTAB) not only acts as a dispersing agent in the bath, but it also acts as a promoter to deposit high amount of B 4C particles (45 vol.%) into nickel matrix owing to its more positive reduction potential than that of the nickel. The anti-wear performance of the nickel coatings reinforced with various amounts of B 4C particle was investigated under dry sliding conditions using an abrasion tester. The anti-wear performance of the Ni/B 4C coating investigated in the present case was comparatively studied with that of the other nickel coatings reinforced with different kinds of hard ceramic particles.

Electroless Formation of Pressure Sensitive Thin Films of Platinum Porphyrin Using Surfactants with an Azobenzene Group

Abstract Pressure sensitive thin films of platinum porphyrin with a polymer binder are prepared by the micelle disruption method using redox-active surfactants with an azobenzene group. Much thinner films can be prepared by this method than conventional methods, which provide a quick time response to pressure changes. Furthermore, the thin films prepared by this method show a good linearity in the Stern–Volmer plot and a high sensitivity to pressure.