Kinetics of silver nanoparticle growth in aqueous polymer solutions

Silver nanoparticles were prepared in aqueous AgNO₃ solution by using hydroquinone and sodium citrate as reducing agents with neutral polymers poly(vinylpyrrolidone) and poly(vinyl alcohol) as stabilizers. The rate of particle formation was determined with a diode array UV-Vis spectrophotometer. The effects of the polymer concentration on the reaction rate, the size, and the size distribution of the particles formed were studied by transmission electron microscopy. Both the reaction rate and the size of silver nanoparticles decreased with increasing polymer concentration in the range 0.07–0.50 w/v%.     

The influence of nanoparticle fillers on the morphology of a spin-cast thin film polymer blend

Polymer/nanoparticle composite films are receiving growing attention thanks to their potential for application in ultra-thin electronic and optical devices. Polymer blend demixing has been shown to be a suitable technique for the structuring of polymer thin films and the patterning of nanoparticles (NP) within them. In this work we show that the morphology of thin polymer films made by spin-casting a polymer blend solution containing NP fillers on a surface depends strongly on the concentration of NP fillers. More specifically, polystyrene/polymethylmethacrylate (PS/PMMA) films formed from a toluene solution, and which demix following a nucleation and growth mechanism, were studied. It was found that both the height and the surface density of PMMA domains increased as the concentration of CoPt:Cu NPs in the film was increased. We find that similar effects are induced in a NP-free PS/PMMA demixed film upon increasing the molecular weight of the PS molecules. This suggests that under certain conditions the NPs and the polymer molecules in the blend do not behave as separate species but form aggregates.     

Vacuum-UV-photolysis of aqueous solutions of citric and gallic acids

The vacuum-UV- (VUV-) photolysis of water is one of the advanced oxidation processes (AOP) based on the production of hydroxyl radicals (HO) that can be applied to the degradation of organic pollutants in aqueous systems. The kinetics of the VUV-photolyses of aqueous solutions of citric acid (1) or gallic acid (2) were investigated in the presence or absence of dissolved molecular oxygen (O₂) and under different pH conditions. In the case of 1, the rate of consumption of the substrate was faster at pH 3.4 than in alkaline solution (pH 11), whereas, in the case of 2, the variation of pH (2.5–7.5) did not affect the course of the reaction. Unexpectedly, the rates of depletion of both 1 and 2 decreased in the absence of O₂, this effect being much more pronounced in the case of 2. In order to explain these results, possible reaction pathways for the degradation of 1 and 2 are proposed, and the roles of the oxidizing (HO) and reducing (H and e_aq⁻) species produced by the VUV-photolysis of water are discussed.     

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.     

Effects of silver nanoparticle doping on the electro-optical properties of polymer stabilized liquid crystal devices

ABSTRACT

Polymer stabilised liquid crystal (PSLC) devices are widely used in various smart light modulation occasions. Their electro-optical properties can still be improved to address future challenges. It is well known that doping liquid crystal (LC) materials with nanoparticles can change the material’s electro-optical performance. In this study, silver nanoparticles (AgNPs) with size about 15–20 nm and surfactant were doped into PSLC devices. The effects of AgNPs doping on the PSLC electro-optical performances were studied. The result shows that AgNPs and surfactant doping can increase the dielectric anisotropy of LC mixture. PSLC devices with AgNPs doping have lower driving voltage and response time than un-doped PSLC devices. Therefore, doping of a specific concentration of AgNPs resulted in PSLC devices with improved electro-optical performance.     

Electrical conductivity of aqueous polymer solutions

 Theoretical equations were proposed to adequately simulate the electrical conductivity behavior of aqueous solutions of both charged and uncharged polymers. The theory, based on the mixture equation of Boned and Peyrelasse, was experimentally verified on poly(acrylic acid) (PAA) in water and poly(ethylene oxide) (PEO) in aqueous electrolyte solutions. The data analysis suggested that both the polymer coils may be depicted as oblate ellipsoids. Subsequently, the semiaxes values of the polymer coils were determined, and they were in good agreement with the results reported in the literature. Received: 25 June 1996 Accepted: 2 October 1996     

Characterization of Mn doped ZnS nanocrystalline powder dispersed in polyvinyl alcohol: 1st Nano Update

Manganese doped zinc sulfide nanocrystalline powder was synthesized with sodium citrate and its films were formed by mixing it with polyvinyl alcohol to study optical absorption of Mn doped ZnS dispersed in polyvinyl alcohol. The characteristics of the prepared powder and film samples were studied by X-ray diffraction, transmission electron microscopy and UV–visible absorption spectroscopy. Samples exhibited optical absorption at lower wavelength region and particle sizes were calculated from X-ray diffractogram.     

Microemulsion method: A novel route to synthesize organic and inorganic nanomaterials: 1st Nano Update

Synthesis of nanoparticles by microemulsion method is an area of considerable current interest. Since the discovery of microemulsions, they have attained increasing significance both in basic research and in different industrial fields. Due to their unique properties, namely, ultralow interfacial tension, large interfacial area, thermodynamic stability and the ability to solubilize otherwise immiscible liquids. The uses and applications of microemulsions are numerous in chemical and biological fields. The nanoparticles not only are of basic scientific interest, but also have resulted in important technological applications, such as catalysts, high-performance ceramic materials, microelectronic devices, high-density magnetic recording and drug delivery. The microemulsion technique promises to be one of the versatile preparation method which enables to control the particle properties such as mechanisms of particle size control, geometry, morphology, homogeneity and surface area. This review aims to give a vivid look on the use of microemulsions for synthesizing and controlling the grain size and morphology of the nanoparticles and at the same time will summarize some recent works carried out in the synthesis of organic and inorganic nanoparticles by this method.     

Hyperbranch-polyethyleniminated functional polymers II: effect of polyethyleniminated polyoxypropylenediamines on copper nanoparticle formation in aqueous solution

Colloidal aqueous solution of zerovalent copper (Cu(0)) nanoparticles were prepared from the Cu²⁺ ions coordinated with polyethyleniminated polyoxypropylenediamines (D400(EI) _x ) followed by chemical reduction of NaBH₄. Aqueous solution of copper clusters formed in the presence of D400(EI)₈ with a loading ratio of [EI]/[Cu²⁺] = 3 were stable without precipitation for standing more than 1 month. The protective effects of D400(EI) _x and the particle size of the resulted Cu nanoparticle are regulated by the attachments of ethylenimine (EI) groups per polymer backbone and the normality ratio of [EI]/[Cu²⁺] used. It is found that the more EI-content per polymer backbone results in the smaller particle size and the narrower size dispersity of the colloidal Cu(0) particles, and the average particle size of 5.07 nm with standard deviation of 0.86 nm was obtained in the presence of D400(EI)₈ with the ratio of [EI]/[Cu²⁺] = 3. As the polymer concentration of D400(EI)₈ increases (the increase of [EI]/[Cu²⁺]), the average particle size of the prepared Cu(0) nanoparticle slightly changes, but interestingly, the size dispersity gradually decreases, where the standard deviation for the concentration at [EI]/[Cu²⁺] = 5 is 0.82 nm approaching that for monodispersed nanoparticles (0.5 nm).     

Assessment of nanoparticle loading and dispersion in polymeric materials using optical coherence tomography

The inclusion of small concentrations of nanoparticles can significantly enhance the thermal and electrical properties, and to a lesser degree the mechanical performance, of polymers. Dispersion of nanoparticles during mixing is problematic, with poor mixing resulting in particle agglomeration (i.e. particle clustering), which subsequently limits the potential for property enhancement. Achieving good dispersion is considered key to large-scale production and commercialization of polymer nanocomposites (PNCs), and a measurement technique capable of quantitatively characterizing particle loading and dispersion would significantly enhance product development. This paper presents the results of a study using a static light scattering technique, Fourier domain optical coherence tomography (FD-OCT), for discriminating between different particle loadings and levels of dispersion. The technique has been applied to a range of PNCs including epoxy resins reinforced with nanoclay platelets, silica microspheres or multi-walled carbon nanotubes (MWCNTs), and zinc oxide and lithium aluminate reinforced polypropylene.     

Assessment of nanoparticle loading and dispersion in polymeric materials using optical wavefront correlation

Small concentrations (≤5 wt. %) of nanoparticles in polymeric materials can potentially result in improvements in material properties and functionality. However, poor or non-uniform particle dispersion resulting in clustering (agglomeration) in polymer nanocomposites (PNCs) limits the potential for property enhancement. Achieving good dispersion is considered essential for large-scale production and commercialization of PNCs. New and effective measurement techniques capable of quantitatively characterizing particle loading and dispersion would significantly contribute towards understanding and optimizing the material performance of PNCs and, consequently, play a pivotal role in product development. This paper presents the results of a study using a static light scattering technique, optical wavefront correlation (OWC), for discriminating between different particle loadings and levels of dispersion. The technique has been applied to a range of PNCs, including epoxy resins reinforced with nanoclay platelets or silica microspheres, and zinc oxide and lithium aluminate reinforced polypropylene.     

Solar active nano-TiO2 for mineralization of Reactive Red 120 and Trypan Blue: 1st Nano Update

Nano-TiO₂ was synthesized by sol–gel method. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) images, transmission electron microscope (TEM), BET surface area measurement and DRS analysis. The formation of anatase phase nano-TiO₂ was confirmed by XRD measurements and its crystalline size is found to be 15.2 nm. SEM images depict the crystalline nature of prepared TiO₂. The BET surface area of prepared TiO₂ is found to be 86.5 m² g^?1 which is higher than that of commercially available TiO₂–P25. The photocatalytic activity of prepared anatase phase TiO₂ has been tested for the degradation of two azo dyes: Reactive Red 120 (RR 120) and Trypan Blue (TB) using solar light. The photocatalytic activity of nano-TiO₂ is higher than TiO₂–P25 under solar light. The mineralization of dyes has been confirmed by chemical oxygen demand (COD) measurements.     

Assessment of nanoparticle loading and dispersion in polymeric materials using oscillatory photon correlation spectroscopy

The inclusion of small concentrations of nanoparticles in polymeric materials (≤5 wt. %) can significantly enhance material properties and functionality. However, poor or non-uniform particle dispersion resulting in particle clustering (agglomeration) in polymer nanocomposites (PNCs) limits the potential for property enhancement in these materials. Achieving good dispersion is considered essential for successful commercialization of PNCs. Hence, reliable and accurate measurement techniques for characterizing particle loading and dispersion would significantly contribute towards understanding and optimizing the material performance of PNCs, and consequently play a pivotal role in product development. This paper, the last of three papers on optical techniques, presents the results of a study using a dynamic light scattering technique, oscillatory photon correlation spectroscopy (Os-PCS), for discriminating between different particle loadings and levels of dispersion. The technique has been applied to two epoxy-based resin systems reinforced with either nanoclay platelets or silica microspheres.     

Measurement of activity coefficients in polymer solutions by the reversedflow technique

Summary The reversed-flow, gas-chromatographic method for measuring activities and activity coefficients in binary liquid mixtures is now extended to the determination of activity coefficients of the solvent in polymer-solvent systems over the whole range of polymer concentration, as well as for the calculation of Flory-Huggins interaction parameters. The parameters found by the present method are compared with those determined by other techniques or calculated theoretically.     

Kinetics of molecular reactions in polymer solutions: Numerical model

The numerical simulation of the kinetics of the molecular interaction in a system containing mobile polymer clusters is performed on the basis of the bond-fluctuation model (BFM). Power-law dependences of the rates of molecular reactions on the concentration of these monomers are observed above the critical concentration. These dependences are related to the features of macromolecular structures in solutions.     

Formation of surfactant and polyelectrolyte gel particles in aqueous solutions

Mixing of oppositely charged surfactants and polyelectrolytes in aqueous solutions can lead to associative phase separation, where the concentrated phase assumes the form of a viscous liquid, gel, or precipitate. This phenomenon can lead to the formation of gel-like particles whose size and polydispersity can be controlled. Here we present phase behavior and structural studies of gel-like particles formed by mixing drops of N,N,N-trimethylammonium derivatized hydroxyethyl cellulose (JR-400) polyelectrolyte solution with oppositely charged anionic and catanionic surfactant solutions composed of sodium perfluorooctanoate (FC₇) and cetyltrimethylammonium bromide (CTAB). Gel formation apparently occurs due to the collapse of the polyelectrolyte chains upon the adsorption of surfactant. This process results in the release of simple ions and water, and yields dense gel-like beads. The diameter of these beads ranges approximately from 200 to 4000 μm. Both the effects of solution composition and the method of preparation are studied by optical and confocal microscopy, and are linked to the structure and stability of the bead. Our observations suggest that the structure of the resulting particles is governed by the solution composition and the method of preparation, while the particle stability is governed by phase behavior alone.     

Role of anions for the reduction behavior of silver ions in polymer/silver salt complex membranes

The reduction of silver ions to silver nanoparticles is an essential issue in polymer/silver salt complex membranes for facilitated olefin transport, because it has a critical influence on the long-term stability of membrane performance. In this study, the role of anions for the formation of silver nanoparticles in polymer/silver salt complexes was investigated. This role was assessed for the complexes of poly(N-vinyl pyrrolidone) (PVP) with three silver salts including AgBF₄, AgCF₃SO₃, and AgNO₃. Especially, UV irradiation to the membranes was used to clearly investigate the reduction behavior of silver ions. Separation performance test, UV–vis spectroscopy and transmission electron microscopy (TEM) clearly show that the reduction rate of silver ions strongly depends on the counteranions of salt, and has the following order: AgBF₄ > AgCF₃SO₃ > AgNO₃. This behavior of the formation of silver nanoparticles in polymer/silver salt complex membranes is explained in terms of the interaction strength of silver ions with the carbonyl oxygens of polymer, and that of silver ions with counteranions. It is concluded that when the former interaction is strong and the latter one is weak, the reduction rate of silver ions to silver nanoparticles is fast, and vice versa. These interactions were characterized using FT-IR, FT-Raman spectroscopy, and theoretical ab initio calculation.     

Adsorption of tartrazine from an aqueous solution by octadecyltrimethylammonium bromide-modified bentonite: Kinetics and isotherm modeling

A modified bentonite was prepared at different surfactant (ODTMA) loadings through ion exchange. The obtained organobentonite adsorbent materials were then used for the removal of an anionic dye, tartrazine, from an aqueous solution. The bentonite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and Brunauer- Emmett-Teller (BET) method. The modification of organophilic bentonite by ODTMA increases the basal spacing d₀₀₁ from 24.1 to 39.1 Å when the cation exchange capacity increases from 1 to 4. The increase in the spacing, due to the basic organic modifications, was confirmed by the results of thermogravimetric analysis, Fourier transform infrared spectroscopy, and BET. The effects of contact time, initial concentration, and solution pH onto an adsorbed amount of tartrazine were investigated. To predict adsorption isotherm, the experimental data were analyzed using the Langmuir and Freundlich isotherm equations. It was determined that the isotherm data were fitted to the Langmuir isotherm. The adsorption process was also found to follow a pseudo-second-order kinetic model.