Silver/silver bromide/polypyrrole nanoparticles obtained by microemulsion photopolymerization in the presence of a cationic surfactant

Conductive silver/silver bromide/polypyrrole nanoparticles were obtained by photopolymerization in o/w microemulsions of pyrrole monomer in the presence of silver nitrate as electron acceptor and dopant under UV light irradiation. The microemulsions were prepared using cetyltrimethylammonium bromide (CTAB) as cationic surfactant. The particles were analyzed by scanning electron microscopy (SEM), UV/Vis, Fourier transform infrared spectroscopy, cyclic voltammetry, and X-ray diffraction (XRD). It was observed from SEM analysis that spherical particles can be obtained by this procedure with relatively narrow particles sizes distributions and average particle diameters of the silver cores (Dp) between 39 and 46 nm, which decreases as the surfactant concentration is increased. The conductivities of the resulting materials were between 0.12 and 0.40 S/m. Formation of cores of Ag and AgBr were observed from the XRD analysis, which was ascribed to the reduction of Ag⁺ to Ag⁰ and to reaction of Ag⁺ with the counterion of CTAB surfactant, respectively.     

Formation and characterization of surfactant stabilized silver nanoparticles: a kinetic study

Kinetic data for the silver nitrate–ascorbic acid redox system in presence of three surfactants (cationic, anionic and nonionic) are reported. Conventional spectrophotometric method was used to monitor the formation of surfactant stabilized nanosize silver particles during the reduction of silver nitrate by ascorbic acid. The size of the particles was determined with the help of transmission electron microscope. It was found that formation of stable perfect transparent silver sol and size of the particles depend upon the nature of the head group of the surfactants, i.e., cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and Triton X-100. The silver nanoparticles are spherical and of uniform particle size, and the average particle size is about 10 and 50 nm, respectively, for SDS and CTAB. For a certain reaction time, i.e., 30 min, the absorbance of reaction mixture first increased until it reached a maximum, then decreased with [ascorbic acid]. The reaction follows a fractional-order kinetics with respect to [ascorbic acid] in presence of CTAB. On the basis of various observations, the most plausible mechanism is proposed for the formation of silver nanoparticles.     

Photo-induced chemical reduction of silver bromide to silver nanoparticles

This paper discusses the experimental results of the production of nanocolloidal silver using photoreduction method. Ultrafine crystalline gelatine-stabilised aqueous suspensions of silver bromide were used as a substrate for the synthesis of silver nanoparticles (Ag NPs). The influences of the reductant to substrate molar ratio, the medium’s pH, the type of the source of actinic radiation and the time of exposure to the efficient production of the Ag NPs were studied. A typical reaction was suggested, which involves the photo-induced reduction of silver bromide nanocrystals in the presence of ascorbic acid under specified physicochemical conditions. The properties of resultant silver particles were examined using UV-Vis spectroscopy and Dynamic Light Scattering (DLS). In addition, Transmission Electron Microscopy (TEM) was used for imaging the silver nanoparticle suspensions.      

Prediction of silver nanoparticles size synthesized in microemulsion system

Nanoparticle synthesis within the aqueous cores of water-in-oil reverse micelle systems is a viable method, which allows control over the size and shape of the particles. The intermicellar exchange rate is affected by the bulk solvent type, the contents dissolved within the core, and the size of the reverse micelle or the water content, referred to as the W value, where W is the molar ratio of the water to surfactant concentrations. In this study a soft sphere model was used to predict ultimate silver nanoparticle particle sizes obtained in AOT reverse micelle. In this model a total interaction energy is implemented to represent the attractive van der Waals forces acting between the metallic particles and the repulsive osmotic and elastic forces, which result from the surfactant tail-tail and solven-tail interactions responsible for the steric stabilization of the metallic particles within the microemulsion. Result from the model accurately predicts the ultimate silver nanoparticle sizes.     

Shape-directing role of cetyltrimethylammonium bromide in the preparation of silver nanoparticles

We report a simple chemical reduction method for the synthesis of different colored silver nanoparticles, AgNP, using tyrosine as a reducing agent. Effects of cetyltrimethylammonium bromide, CTAB, and tyrosine concentrations are analyzed by UV-visible measurements and scanning electron microscopy (SEM) to evaluate the mode of AgNP aggregation. The position and shape of the surface resonance plasmon absorption bands strongly depend on the reaction conditions, i.e., [CTAB], [tyrosine], and reaction time. Sub-, post-, and dilution-micellar effects are accountable for the fast and slow nucleation and growth processes. Spectrophotometric measurement also shows that the average size and the polydispersity of AgNP increase with [CTAB] in the solution. CTAB acted as a shape-directing agent.     

Formation of colloidal silver in the presence of a nonionic surfactant,Surfynol 465

The formation of colloidal silver in the presence of a nonionic surfactant, Surfynol 465, was studied at various temperatures. By simply mixing equal volumes of AgClO₄ aq. (1–10 mmol kg^–1) and Surfynol 465 aq., the colloidal silver was formed. The colloidal solution had well over ten times the amount of fine silver particles in the solution formed by the ordinary methods. The first factor to form the colloidal silver without aggregation was the molar ratio of Surfynol 465 to AgClO₄, and the optimum ratio increased with increasing the concentration of AgClO₄ or the temperature. In the fraction of colloidal silver collected through the gel filtration, Surfynol 465 was also found in the micellar state. From these results, it was suggested that Surfynol 465 was a protecting agent of colloidal silver as well as a reducing agent of AgClO₄ in the similar manner to the case of colloidal gold.     

Stochastic collision electrochemistry of single silver nanoparticles

The electrochemical oxidation of single colloidal Ag nanoparticles (NPs) at an electrode surface has previously been studied as an in situ particle-sizing methodology. However, the discovery of multipeak amperometric behavior in 2017 sparked new interest toward understanding the precise physical mechanism of the manner in which a freely diffusing Ag NP interacts with the electrode surface. Random walk simulations, unique electrochemical experiments, and correlated optical/spectroscopic techniques have revealed exciting new results regarding the physical and chemical processes occurring on single NP collision.     

Studies on the kinetics of growth of silver nanoparticles in different surfactant solutions

We produced gels using electrolytic-reduction ion water and magnesium aluminum silicates (smectone^®), and evaluated in detail gel properties in the presence of various types of salt (NaCl, KCl, CaCl₂, MgCl₂, and AlCl₃). Each salt was added to deionized-distilled water or electrolytic-reduction ion water, and phase diagrams for the smectone^® concentration (2.0–4.0%) were produced. The areas of the three phases of smectone^® (gel, sol, and separation) at each salt concentration were expressed as percentages of the total area. As a result, uni- and polyvalent cations (excluding Ca²⁺ ions) affected the stability of gels produced using electrolytic-reduction ion water, and, particularly, univalent cations (Na⁺, K⁺) markedly improved gel stability.Using electrolytic-reduction ion water as a dispersal medium, drug delivery systems (DDS) that can maintain the gelling state can be prepared. Thus, gel preparations with maintained functions or controlled-release transdermal drugs can be obtained.     

Effects of urea and a nonionic surfactant on the micellization and counterion binding properties of cetyltrimethyl ammonium bromide and sodium dodecyl sulfate

Micellization characteristics and counterion binding properties of cetyltrimethyl ammonium bromide (CTAB) in presence of urea and a nonionic surfactant polyoxyethylene sorbitan monolaurate (PSML), and of sodium dodecyl sulphate (SDS) in presence of urea as well as of several mixtures of CTAB with a bile salt, sodium cholate (NaC), and sodium chloride have been studied. Both urea and PSML have increased the critical micelle concentration (CMC) of the surfactants, the former being more effective than the latter. The analysis of the results supports the pseudophase micellar model to hold over the mass action model. Pure CTAB micelles bind more counterions (96 %) than pure SDS micelles (87 %), and the decreasing effect of urea on the binding is less in case of the former than the latter. A 41 mixture of CTAB and sodium cholate (NaC) can micellize and the micelles bind 87 % bromide ion, whereas 21 and 11 mixtures do not micellize. Micelles of 11 mixture of CTAB and NaCl can bind counter bromide ions to the extent of 92 %. The limiting concentrations of urea required to effect counterion binding by CTAB and SDS micelles are 0.15 mol dm^–3 and 0.25 mol dm^–3, respectively. Such effect is shown by PSML on CTAB at a ratio 0.281. The activation energy of conduction of SDS has increased in the presence of urea up to a concentration of 4 mol dm^–3, at higher concentrations the activation energy has decreased, the effect being more for surfactant concentration above CMC than below.     

Surfactant-assisted synthesis and characterization of stable silver bromide nanoparticles in aqueous media

Colloidal dispersions of silver bromide (AgBr) in aqueous surfactant medium have been prepared using a surfactant-assisted synthesis approach with hexadecyltrimethylammonium bromide (CTAB). The surfactant acts both as source of bromide ion as well as the stabilizing agent. Upon progressive addition of silver nitrate to aqueous CTAB solution, stable AgBr dispersions were obtained. Formation of surfactant cation (CTA(+)) stabilized AgBr was confirmed by way of XRD, FTIR and NMR studies. Thermal behavior of the isolated nanoparticles was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), where the occurrence of phase transition in the surfactant-stabilized nanoparticles was observed. Kinetics of the particle growth was investigated by dynamic light scattering measurements, which predicted the formation of surfactant bilayered structures associated with the nanoparticles of AgBr. Band gap of the nanoparticles was determined by suitably analyzing the UV-visible spectral data, which concluded that the particles behaved like insulators. Morphology of the particles, studied by TEM measurements, was found to be spherical. Finally, enthalpy of formation of surfactant-stabilized AgBr, determined calorimetrically, was found to be dependent on the concentration of the precursors.     

微乳胶粒的形成与表面活性剂的作用——粗粒化力场分子动力学模拟研究

从微观机理上研究表面活性剂对微乳胶粒形成的影响有利于推动微乳状液在各个领域的应用研究．本文采用分子动力学模拟方法研究了微乳胶粒的形成过程及表面活性剂对微乳胶粒形成的影响．正十二烷（C12H26）和十二烷基硫酸钠（SDS）作为油分子和表面活性剂分子的模型,Martini粗粒化（coarse．grained,CG）力场描述分子间和分子内的相互作用,对含有不同浓度的正十二烷和表面活性剂的12个模型分别进行了100ns的分子动力学模拟．模拟结果显示,不含表面活性剂的体系迅速发生水油相分离,且分离过程伴随着势能的明显下降;含有表面活性剂的体系中,在相同时间内通过模拟得到了稳定的、表面活性剂分子包裹油分子的胶粒．对不同温度下模拟得到的数据分析发现,胶粒形成初期的动力学特征可以近似地表达为二级反应,聚集活化能为14．6kJ／mol．     

Impact of silver nanoparticles synthesized by green method and microemulsion loaded with the nanoparticles on the development of cress

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银纳米粒子共振光散射光谱法测定痕量CTMAB

利用十六烷基三甲基溴化铵(CTMAB)与银纳米粒子作用生成的聚集体,使体系的共振光散射(RLS)强度明显增强,建立了一种快速、简便的测定痕量CTMAB的RLS光谱法。考察了p H值,反应最佳时间,试剂加入顺序等因素对测定CTMAB的影响。实验结果表明,在p H值为10.88,作用时间为10 min,银纳米粒子浓度(以银原子计算)为2.5×10-3mol·L-1,按CTMAB、BR、银纳米粒子为添加顺序的条件下,测定CTMAB的线性范围为:5.0×10-9~5.0×10-7mol·L-1,检出限为3.8×10-9mol·L-1。该法用于合成样品中CTMAB的测定,灵敏度高,重现性好,结果准确。     

Formation of the bimodal ensemble of silver nanoparticles in polymer solutions

Silver nanoparticles synthesized in polymer solutions are studied by spectroscopy (in near ultraviolet, visible, and infrared spectral regions) and high-resolution transmission electron microscopy. It is established that the ensemble with bimodal particle size distribution is formed from initially polydisperse nanoparticle ensemble in methylhydroxy ethyl cellulose solution. In contrast to the classical scheme of the ripening of colloidal dispersions, the number of small particles increases with time in the studied system; moreover, particles with a size of about 2 nm turned out to be stable. The large particles grow with time and their concentration drops.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 87–93. Original Russian Text Copyright © 2005 by Serebryakova, Uryupina, Roldughin.     

Morphology and size-controlled synthesis of silver nanoparticles in aqueous surfactant polymer solutions

We have employed a number of reducing and capping agents to obtain Ag(0) metallic nanoparticles of various sizes and morphologies. The size and morphology were tuned by selecting reducing and capping agents. Spherical particles of 15 and 43 nm diameter were obtained when 1 wt% aqueous starch solution of AgNO₃ precursor salt was reduced by d(+)-glucose and NaOH, respectively, on heating at 70 °C for 30 min. Smaller size particles obtained in the case of d(+)-glucose reduction has been attributed to the slow reduction rate by mild reducing agent d(+)-glucose compared to strong NaOH. Conducting the reduction at ambient temperature of silver salt in liquid crystalline pluronic P123 and L64 also gave spherical particles of 8 and 24 nm, respectively, without the addition of any separate reducing agent. NaOH reduction of salt in ethylene glycol (11 g)/polyvinyl pyrolidone (PVP; 0.053 g) mixture produced large self-assembled cubes of 520 nm when smaller (26–53 nm) star-shaped sharp-edged structures formed initially aggregated on heating the preparation at 190 °C for 1 h. Increasing the amount of PVP (0.5 g) in ethylene glycol (11 g) and heating at 70 °C for 30 min yielded a mixture of spherical and non-spherical (cubes, hexagons, pentagons, and triangle) particles without the addition of an extra reducing agent. Addition of 5 wt% PVP to 1 wt% aqueous starched solution resulted in the formation of a mixture of spherical and anisotropic structures when solution heated at 70 °C for 1 h. Homogeneous smaller sized (29 nm) cubes were synthesized by NaOH reduction of AgNO₃ in 12.5 wt% of water-soluble polymer poly(methyl vinyl ether) at ambient temperature in 30 min reaction time.     

Formation of silver nanoparticles in formamide:water mixtures: a radiolytic study

The pulse radiolysis of FA and FA:water solutions was studied in the absence and presence of redox indicator 1,1′-dimethyl-4,4′-bipyridinium dichloride (methyl viologen, MV²⁺). The experiments performed in the presence of MV²⁺ have provided strong support to the idea that the first species obtained from the reaction of e_sol⁻ and ^•OH with FA produces radicals that show reactivity towards the MV²⁺. Both the radicals on reaction with MV²⁺ results in the appearance of the well-known intense blue MV^•+ radical absorption signal (λ_max = 395 nm, λ_max = 605 nm). The intermediate radicals formed during radiolysis were used to generate silver nanoparticles.     

Formation of silver nanoparticles and nanocraters on silicon wafers

Silver nanocraters and monodisperse nanoparticles were formed on silicon wafers by spin-coating of an aqueous AgNO3/PVA solution and calcination of the resulting Ag+/PVA composite film. The monodisperse Ag nanoparicles were formed from small Ag+/PVA aggregates and were uniformly and stably distributed on the substrate surface. They were located as close as 2.8 nm apart (edge to edge) without coalescence. This nanoparticle stability was apparently derived from their interaction with the oxidized wafer surface. On the other hand, Ag metallic nanocraters with and without nanodots at their centers were produced from large Ag+/PVA aggregates. The explosive decomposition of AgNO3 and PVA by calcination could explain their formation. When Ag+ ions were reduced to Ag nanoparticles prior to calcination, larger Ag nanoparticles were produced probably due to aggregation of closely situated nanoparticles. Those nanoparticles that were located far enough stayed intact. Perspectives are discussed in terms of potential applications.     

Effect of surfactant counterion and organic modifier on the properties of surfactant vesicles in electrokinetic chromatography

Counterion and organic modifier are two parameters in EKC that can be varied in order to obtain improved solubility, selectivity, and efficiency. The effect of changing surfactant counterion and/or organic modifier on the chromatographic and electrophoretic properties of cetyltrimethylammonium bromide (CTAB)/sodium octyl sulfate (SOS) vesicles is examined in EKC. The vesicles are prepared in a 1:3.66 cationic/ anionic mole ratio for a total surfactant concentration of 69 mM. The cationic CTAB is replaced by cetyltrimethylammonium chloride (CTAC) and the first use of CTAC/SOS vesicles is reported. The mean diameter of the CTAC/SOS vesicles is 96 nm while that of the CTAB/SOS vesicles is 85 nm. A class I modifier (2-amino-1-butanol) and a class II modifier (acetonitrile) have similar effects on the EOF, elution range, methylene selectivity, and the efficiency of the CTAB/SOS vesicles and the CTAC/SOS vesicles. Upon addition of 10% ACN, there is roughly a 10-fold increase in the efficiency of heptanophenone, a model hydrophobic compound, compared to the efficiency using unmodified vesicles. Linear free energy relationship (LFER) analysis using the Abraham solvation model is employed to characterize solute-vesicle interactions. The results suggest that organic modifier-vesicle interactions depend somewhat on the counterion.