Electromagnetic fields around silver nanoparticles and dimers

We use the discrete dipole approximation to investigate the electromagnetic fields induced by optical excitation of localized surface plasmon resonances of silver nanoparticles, including monomers and dimers, with emphasis on what size, shape, and arrangement leads to the largest local electric field (E-field) enhancement near the particle surfaces. The results are used to determine what conditions are most favorable for producing enhancements large enough to observe single molecule surface enhanced Raman spectroscopy. Most of the calculations refer to triangular prisms, which exhibit distinct dipole and quadrupole resonances that can easily be controlled by varying particle size. In addition, for the dimer calculations we study the influence of dimer separation and orientation, especially for dimers that are separated by a few nanometers. We find that the largest /E/2 values for dimers are about a factor of 10 larger than those for all the monomers examined. For all particles and particle orientations, the plasmon resonances which lead to the largest E-fields are those with the longest wavelength dipolar excitation. The spacing of the particles in the dimer plays a crucial role, and we find that the spacing needed to achieve a given /E/2 is proportional to nanoparticle size for particles below 100 nm in size. Particle shape and curvature are of lesser importance, with a head to tail configuration of two triangles giving enhanced fields comparable to head to head, or rounded head to tail. The largest /E/2 values we have calculated for spacings of 2 nm or more is approximately 10(5).     

Spontaneous formation of silver nanoparticles in aminosilica

We report a rapid and spontaneous metallization process associated with sol–gel reaction of aminosilane that can be utilized to synthesise silver embedded silica nanocomposite without involving additional reducing agents. The reduction reaction induced by bis[3-(trimethoxysilyl)propyl]ethylenediamine (enTMOS) involves amine functional moieties, which drive the reduction reaction with presence of water. Cyclic voltammetry was used to investigate the redox potential of enTMOS and its relation to chemical environment. It was found that the oxidation potential of enTMOS depending on the amount of water (water:enTMOS (v/v) = 8:1–0:1) ranges from 0.48 to 0.68 V versus Ag/AgCl electrode in methanol. The oxidation potential of aminosilane decreases with water content and becomes more negative than that of Ag, suggesting the aminosilane acts as a silver reducing agent while serving as a matrix to encapsulate silver nanoparticles after reacting with water. This process has been utilized to produce evenly dispersed silver nanoparticles with sizes ranging from 5 to 20 nm in both liquid and solid forms of aminosilane, allowing us to prepare silver nanoparticles doped silica nanocomposite that exhibits enhanced electrochemical properties.     

Kinetics of the droplet formation at the early and intermediate stages of the spinodal decomposition in homopolymer blends

The kinetics of the droplet formation during the spinodal decomposition (SD) of the homopolymer blends has been studied by numerical integration of the Cahn‐Hilliard‐Cook equation. We have found that the droplet formation and growth occurs when the minority phase volume fraction, f_m , approaches the percolation threshold value, f_thr = 0.3 ± 0.01. The time for the formation of the disperse droplet morphology (coarsening time) depends only on the equilibrium minority phase volume fraction, f_m . f_m approaches its equilibrium value logarithmically at the late SD stages, and, therefore, the coarsening time decreases exponentially as the average volume fraction or the quench depth decrease. Since the temporal evolution of the total interfacial area does not depend on the quench conditions and blend morphology, the average droplet size and the droplet number density is determined by the coarsening time. Within the time scale studied, the droplet number density decreases with time as t ^{–0.63±0.03}; the average mean curvature decreases as t ^{–0.35±0.05}; the average Gaussian curvature decreases as t ^{–0.42±0.03}, and the average droplet compactness ˜V/S^3/2 where S is the surface area and V is the volume) approaches a spherical limit logarithmically with time. The droplets with larger area have lower compactness and in the low compactness limit their area is a parabolic function of compactness. The size and shape distribution functions have been also investigated.     

Photochemical formation of silver nanoparticles in elastomer films

Photochemical deposition of silver nanoparticles in poly(butyl acrylate) and poly(butadiene-styrene) under the action of monochromatic UV light (254 nm) was studied. Changes in the polymer structure in the course of photolysis were revealed and analyzed. A mechanism of formation of silver nanoparticles was suggested. Electron microscopic examination showed that the efficiency of the particle formation is determined by the residual moisture content of the polymer films. Physicomechanical properties (tensile strength and relative elongation) of the elastomer films containing silver nanoparticles were studied.     

Role of phenol derivatives in the formation of silver nanoparticles

We demonstrate that dihydroxy benzenes are excellent reducing agents and may be used to reduce silver ions to synthesize stable silver nanoparticles in air-saturated aqueous solutions. The formation of Ag nanoparticles in deaerated aqueous solution at high pH values suggests that the reduction of silver ions occurs due to oxidation of dihydroxy benzenes and probably on the surface of Ag2O. Pulse radiolysis studies show that the semi-quinone radical does not participate in the reduction of silver ions at short time scales. Nevertheless, results show that primary intermediates undergo slower transformation in the presence of dihydroxy benzenes than in their absence. This slow transformation eventually leads to the formation of silver nanoparticles. The Ag nanoparticles were characterized by UV-vis absorption spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). XRD and TEM techniques showed the presence of Ag nanoparticles with an average size of 30 nm.     

Kinetics of formation of intermediates in silver ion assisted aquations

There is kinetic evidence of the formation of [Co(NH₃)₅NCSAg₃]⁵⁺ in the interaction of [Co(NH₃]⁵NCS]²⁺ with Ag⁺ in aqueous solution, with pseudo-first-order formation rate constant k = 0.158 s⁻¹ for the forward reaction in the following equation at 25°C and [Ag⁺] in the range of 1.23–5.0 × 10⁻² mol dm⁻³ and 0.10 ionic strength (NaClO₄):

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Additionally, the formation constant, β₂, for [Co(NH₃)₅NCSAg₂]⁴⁺ has been determined to be log β₂ = 4.717. For the [Rh(NH₃)₅I]²⁺-Ag⁺ reaction there is evidence of an outer-sphere interaction with rate constants of k₂ = 670 dm³ mol⁻¹ s⁻¹ at 25°C and 0.10 ionic strength. This outer-sphere species undergoes further reaction to give the silver ion containing intermediates of the aquation reactions.     

Kinetics and mechanism of the formation of silver nanoparticles by reduction of silver (I) with maltose in the presence of some active surfactants in aqueous medium

The kinetics and mechanism of the formation of silver nanoparticles by reduction of Ag⁺ with maltose were studied spectrophotometrically by monitoring the absorbance change at 412 nm in aqueous and micellar media at a temperature range 45–60 °C. The reaction was carried out under pseudo-first-order conditions by taking the [maltose] (>tenfold) the [Ag⁺]. A mechanism of the reaction between silver ion and maltose is proposed, and the rate equation derived from the mechanism was consistent with the experimental rate law. The effect of surfactants, namely cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecyl sulfate (SDS, an anionic surfactant), on the reaction rate has been studied. The enthalpy and the entropy of the activation were calculated using the transition state theory equation. The particle size of silver sols was characterized by transmission electron microscopy and some physiochemical and spectroscopic tools.     

Photo- and temperature-dependent formation of tryptophan/silver nanoparticles

Research on Chemical Intermediates - Amino acid tryptophan is an advantageous reagent for preparation of biocompatible noble metal nanoparticles as promising anticancer agents. The reduction of...     

Correction to: Photo- and temperature-dependent formation of tryptophan/silver nanoparticles

Research on Chemical Intermediates - In the original publication of the article, the co-author’s name was incorrectly published as “O. N. Kachalova”.     

Features of the formation of silver nanoparticles on the silicon nitride surface

Special features of the formation of particles of a silver-containing catalyst phase on a silicon nitride surface in relation to the mode of the active component deposition were studied. The influence of a redox medium of the catalytic reaction of the ethylene glycol selective oxidation to glyoxal on the final composition and structure of silver catalysts was studied.     

Photo-induced formation of silver nanoparticles and polymerization of acrylamide derivatives

The effect of silver ions and silver nanoparticles on the rate of polymerization of acrylamide and N-isopropylacylamide was investigated. Composites of silver particles of diameter around 30 nm and polyacrylamide were prepared by the photochemical method in the absence of any photosensitizer. The particles formed were characterized by UV–visible spectrophotometry, XRD, and TEM. It was shown that the presence of metal ions such as Ag⁺, Co²⁺, and Ni²⁺ in the acrylamide monomer is essential for photoinduced polymerization.     

Kinetics of dissolution of silver nanoparticles inside triton N-42 reversed micelles

Our spectrophotometric study of the kinetics of dissolution of silver nanoparticles by nitric acid inside inverted micelles of Triton N-42 (a nonionic surfactant) verified the universal character of the mechanism for this type of process, which includes the interaction of surface metal atoms with an oxidizer in two routes: either with (autocatalysis) or without newly formed ionic species of the oxidized metal. Effective rate constants for both routes are independent of the value of solubilization capacity (V _s /V _o is the ratio of the volume of the dispersed aqueous phase to the volume of the micellar solution); the solubilization capacity is useful to control the micelle and particle sizes: k ₁ = 0.018±0.003, 0.010±0.003, and 0.012±0.003 s⁻¹ and k ₂ = 2.5±0.8, 1.5±1.1, and 1.4±0.4 L/(mol s) for 100 V _s /V _o = 1, 2, and 3%, respectively.     

Effect of the polymer matrix on the formation of silver nanoparticles in polymer–silver salt complex membranes

When polymer–silver salt complex membranes were exposed to UV irradiation, the separation performances of both the permeance and selectivity for propylene–propane decreased, which was primarily attributed to the reduction of the silver ions in the membranes to silver nanoparticles. Here, the effect of the polymer matrix on the formation of silver nanoparticles in the polymer–silver salt complex membranes was investigated. This effect was assessed for the complexes of two kinds of silver salts (AgBF₄ and AgCF₃SO₃) with several polymeric ligands containing three different carbonyl groups, including poly(vinyl pyrrolidone) (PVP) with an amide group, poly(vinyl methyl ketone) (PVMK) with a ketone group, and poly(methyl methacrylate) (PMMA) with an ester group. UV–vis spectra and transmission electron microscopy (TEM) images clearly indicated that the reduction rate of the silver ions has the following order in the various polymer matrices: PVP > PVMK > PMMA, whereas the size and the distribution of the nanoparticles exhibited the reverse order. The tendency to form silver nanoparticles was explained in terms of the differences between the comparative strengths of the interactions of the silver ions with the different carbonyl oxygens in the matrices, as well as that of the silver ions with counteranions, which was characterized by X‐ray photoelectron spectroscopy (XPS) and FT‐Raman spectroscopy. It was concluded that when the concentration of free silver ions was low due to weak polymer–silver ion and strong silver ion–anion interactions, as found with PMMA, the reduction rate of silver ions to silver nanoparticles was slow. Therefore, the PMMA–silver complex membranes were less sensitive to decreases in separation performance upon UV irradiation than compared to the PVP membranes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1168–1178, 2006     

In situ formation of silver nanoparticles in PMMA via reduction of silver ions by butylated hydroxytoluene

Silver nanoparticles (Ag NPs) were efficiently generated by in situ reduction of silver ions via butylated hydroxytoluene (BHT), in poly(methyl methacrylate). The characterization of Ag/PMMA by TEM, SEM, XRD, and FTIR indicated that Ag NPs with a face center cubic (fcc) crystal structure and a mean diameter of about 30 nm were dispersed in PMMA matrix with a relatively uniform distribution. In addition, the results of UV–Vis spectroscopy indicated that optical properties of the nanocomposite appeared mainly dependent on the reaction time and temperature. Increasing the reaction time and temperature make higher yield of Ag NPs. A provisional reduction mechanism was also proposed for the formation of the Ag NPs.     

Size quantized formation and self-assembly of gold encased silver nanoparticles

Mixing aqueous dispersions of thiocyanate ion coated small (< 3.5 nm diameter) gold nanoparticles and EDTA covered larger (> 22 nm diameter) silver nanoparticles, results in the formation of robust gold encased silver nanoparticles; in contrast to using larger (> 11 nm diameter) gold nanoparticles which forms chained structures.     

Regularities of the formation of silver nanoparticles with oligostyrylmonocarboxylate ligands in ED-20 oligomer

Regularities of the formation of silver nanoparticles according to the reduction reaction of silver oligostyrylmonocarboxylate with ED-20 resin in the absence of hardening agent were studied at 60–75°C by UV/Vis spectroscopy and IR spectroscopy, transmission electron microscopy, and viscosimetry. Spherical silver nanoparticles with oligostyrylcarboxylate ligands characterized by diameter equal to 1.8 ± 0.2 nm and tendency toward ordered disposition in space were obtained. The process of formation of nanoparticles includes consecutive formation of diphilic complexes of silver carboxylate with epoxy resin, Ag⁺ → Ag⁰ reduction, and formation of (Ag⁰) _n nuclei at the ends of the diexpoxy component and/or along the oligomer chain. The activation energy values of formation of nanoparticles during the “inductive period” and at the stage of accumulation as well as the activation energy of viscous flow of ED-20 were measured. The threshold temperature of formation of narrow-size silver nanoparticles in epoxy oligomer ED-20 equals 75°C.     

Thermostimulated formation of silver and gold nanoparticles in porous silicon dioxide matrices

Manifestations of thermostimulated formation and subsequent transformation of silver and gold nanoparticles in porous opal and Vycor glass matrices are studied using optical spectroscopy. Two temperature ranges for silver nanoparticles are revealed, where first-type particles transform into another type of particles. With gold nanoparticles in these matrices, a temperature range in which one type of particles transforms into another type is established. An effect of complete blackening of Vycor glass samples, caused by their annealing, is revealed, and a rationalization of this effect is given.     

Thermochemical study of silver halide nanoparticles formation conditions in AOT inverted micelles

AgCl and AgBr nanoparticles formation conditions were studied by a thermochemical method in AOT (sodium bis(2-ethylhexyl)sulfosuccinate) inverted micellar systems, in AOT—dioctyl sulfide (DOS) mixed micelles, and (for comparison) in aqueous solutions. The heats of formation of AgCl and AgBr nanoparticles in AOT micelles in exchange reactions with potassium halides are, respectively, −55.5 × (1 ± 0.07) and −68.6 × (1 ± 0.07) kJ/mol, that is, smaller in magnitude than the values obtained for aqueous solutions (−68 × (1 ± 0.07) and −88 × (1 ± 0.07) kJ/mol). This difference arises from the existence of particle interactions causing the formation of coagulation contacts between halide particles followed by precipitation in an aqueous phase and the absence of such interactions in a micellar medium. DOS interacts with AOT (to form mixed micelles) and with silver ions (in long-term contact), thus reducing the heats of reactions.