Thermo-optical properties of silver and gold nanofluids

This work focuses on the study of thermal diffusivity and physical properties of nanofluids with very low concentrations of silver or gold nanoparticles. Thermal measurements were performed by means of thermal lens spectroscopy in the dual beam configuration. Improvements of 20 and 16 % in the thermal diffusivity were observed for silver and gold nanofluids, respectively, in comparison with pure water. The estimation of the size distribution of the metallic nanoparticles was obtained through the fitting of the extinction spectra via Mie theory and images of field emission gun scanning electron microscopy.     

PVP催化还原及稳定化纳米银的微波合成

在聚乙烯基吡咯烷酮(PVP)的存在下,微波辐射硝酸银水溶液,合成了纳米银/PVP复合物。UV-Vis和XRD结果证明了生成的纳米银具有面心立方结构,PVP中N原子对银离子具有催化还原作用。TEM结果表明纳米银粒径在10～25nm,且较均匀分散在聚合物基体中;XPS结果表明PVP与纳米银之间存在相互作用。     

One-pot synthesis of bis-1,5,3-dithiazepanes and their sorption properties toward silver(I) and palladium(II)

The possibility of one-pot synthesis of bis-1,5,3-dithiazepanes by multicomponent condensation of amines (NH₄Cl, hydrazine, and 1,2-ethylenediamine) with formaldehyde and 1,2-ethanedithiol was described. Their sorption properties relative to Ag(I) and Pd(II) were studied by a static method. It was shown that at room temperature bis-1,5,3-dithiazepanes recovered with high efficiency silver(I) and palladium(II) from nitrate solutions and hydrochloric acid solutions, respectively.     

Hydrogels of polyvinylpyrrolidone (PVP) and poly(acrylic acid) (PAA) synthesized by radiation-induced crosslinking of homopolymers

pH-sensitive PVP–PAA hydrogels have been prepared by electron-beam-induced irradiation at pH close to pKa of carboxylic groups. Protonation of these groups promoted the formation of hydrogen bonds between the PAA and PVP segments within the crosslinked structure and caused interpolymer complex formation. To demonstrate possible future application of such gels, we tested them as simple chemical detectors. When loaded with glucose oxidase, the PAA–PVP gel's turbidity and shrinkage was triggered by the presence of glucose due to a drop in pH caused by the enzymatic reaction.     

Determination of total polyvinylpyrrolidone (PVP) in ophthalmic solutions by size exclusion chromatography with ultraviolet-visible detection

A straightforward size exclusion chromatography (SEC) method was developed and validated for the determination of total polivinylpyrrolidone (PVP) in ophthalmic solutions using the unusual combination of size exclusion chromatography (SEC), ultraviolet-visible detection and quantitation of an analyte peak that elutes in the total exclusion volume of the column. Samples of opthalmic solutions are diluted with water and injected onto a TSKgel G1000PW, 7.5 mm i.d. × 30 cm, 12 μm column at 50°C, with 80:20 0.1M sodium acetate-methanol mobile phase and UV detection at 220 nm. Validation was successful for a stability indicating pharmaceutical method, with parameters including specificity, accuracy, linearity, and precision within typical pharmaceutical acceptance criteria. A stress study with acid, base, peroxide, heat, and light indicates that there is no interference from drug, product, or excipients.     

Electrical transport properties of poly(aniline-co-p-phenylenediamine) and its composites with incorporated silver particles

Statistical copolymers of aniline and p-phenylenediamine, poly(aniline-co-p-phenylenediamine)s, were synthesised by oxidative polymerisation using various oxidants, ammonium peroxydisulphate or silver nitrate. Depending on the choice of oxidant, copolymers or composites with silver particles were obtained. Different molar concentrations of p-phenylenediamine in the reaction mixture provided materials of different conductivities. The influence of both the copolymer composition and the presence of discrete silver particles on the electric and dielectric properties of the system was studied. The results showed a decrease in the conductivity of copolymers and their composites with the silver content compared with the content of standard polyaniline salt. The reduction in conductivity was described in terms of the decreased density of hopping centres due to defects in the copolymer structure. The dielectric relaxations observed were described in terms of their activation energies and were linked to the corresponding conduction mechanism.     

PVP and G1.5 PAMAM dendrimer co-mediated synthesis of silver nanoparticles

PVP and G1.5 PAMAM dendrimer co-mediated silver nanoparticles of smaller than 5 nm in diameter were prepared using H₂ as reducing agent. With the TEM micrograph, it was found that the molar ratios of PVP and G1.5 PAMAM dendrimer have significant effect in the morphology and size distribution of silver nanoparticles. The reaction rate (fitting a first-order equation) was strongly influenced by the molar ratios of PVP and G1.5 PAMAM dendrimer and the reaction temperature. From the UV-Vis spectra of an aqueous solution of silver nanoparticles, they could be stored for at least 2 months without coagulation at room temperature.     

Well-dispersed ultrafine nitrogen-doped TiO_2 with polyvinylpyrrolidone(PVP) acted as N-source and stabilizer for water splitting

In this paper, ultrafine nitrogen-doped TiO_2 photocatalyst with enhanced photocatalytic water-splitting properties was successfully fabricated via a solvothermal method. Herein, polyvinylpyrrolidone(PVP) was used as both nitrogen source and stabilizer. The enhancement in water-splitting process can be attributed to the doping of element nitrogen, which could supply an intermediate energy level and promote the separation of photo-excited holes and electrons. Moreover, this paper provides a new application of high-molecular polymer to synthesize solar-driven water-splitting photocatalysts.     

Formation of gold and silver nanostructures within polyvinylpyrollidone (PVP) gel

Study on reduction of Au(III) and Ag(I) and the formation of Au and Ag nanostructures was performed on the gels of metal precursor and PVP polymer mixture. Some comparing samples were prepared for better understanding the role of reactants on the reduction of metal ions and further growth of nanocrystals. The results suggest that, in addition to its function of generating stable colloids, PVP not only has a reducing effect on metal ions, but also acts as a crystal growth modifier. At low temperatures, the reducing effect of PVP is strong on Ag(I) ions in AgNO₃, while the reduction of complex Au(III) ions in HAuCl₄ is slow, involving two steps of Au(III)→Au(I)→Au. In the study of temperature disturbance on crystal growth, Au nanoplates of new and well-defined star shape were observed. The differences in the size and shape of nanoparticles are discussed from the colloid chemistry.     

Influence of polyvinylpyrrolidone (PVP) on alumina sols prepared by a modified Yoldas procedure

Al₁₃ polycations containing alumina sols, prepared by a modified Yoldas procedure were mixed with polyvinylpyrrolidone (PVP). Although Al speciation in freshly prepared sols was not affected by PVP addition the decay rate of Al₁₃ polycations was slightly decreased in PVP-containing sols. PVP does not show any influence on particle size and particle growth. The influence of PVP addition on viscosity and flow behavior of modified Yoldas sols depends on their solids content and molar ratio.     

Influence of aquo-organic solvent media on the self-aggregation of sodium dodecyl sulfate (SDS) and its interaction with polyvinylpyrrolidone (PVP)

Influence of mixed aquo-organic solvents viz. water-dimethyl sulfoxide (DMSO), water-formamide (FA), water-dioxane (DX), and water-ethylene glycol (EG) on the micellization of sodium dodecylsulfate (SDS) alone and in presence of neutral polymer polyvinyl pyrrolidone (PVP) was studied. Interaction with PVP initially witnessed formation of critical aggregation concentration (CAC) in the favor of formation of induced small micelles of SDS at a concentration lower than the normal critical micelle concentration (CMC), and later found the formation of normal micelles with extended critical micelle concentrations (CMC_e) in solution. The SDS-PVP interaction depended on the nature and composition of the mixed solvents. Besides CAC and CMC_e, the maximum Gibbs surface excess at the interface (Γ _max), the minimum area (A _min) of the dissociated amphiphile anion, and enthalpy of micellization (ΔH _m ⁰ ) were also determined. Configurational state of PVP in aquo-organic media was investigated by the methods of viscometry, dynamic light scattering (DLS), and scanning electron microscope (SEM) methods. The [η] and Huggins constant (k _H) were considered to ascertain the overall configuration of PVP in solution. The complexes were formed and aggregated at different stages of their molecular composition. The aggregate sizes were determined by DLS, and the surface morphologies in the solvent removed states were examined by SEM. With reference to bulk and interfacial phenomena, polymer-surfactant interaction is thus considered to be important, and the detailed study herein under taken for SDS-PVP combination and PVP alone in mixed aquo-organic solvent media is a new sort of attempt. Figure

DX and DMSO influenced [η] of PVP, SDS interacted PVP enthalpogram and the SEM image of the PVP in 10 wt% DX     

Improved polyvinylpyrrolidone (PVP)/graphite nanocomposites by solution compounding and spray drying

In order to evaluate the roles of graphite dispersion on the functional properties of the composites, PVP/graphite nanocomposites were prepared by blending the aqueous suspension of expanded graphite sheets and polyvinylpyrrolidone (PVP) aqueous solution by ultrasonic treatment, followed by spray drying and direct drying as a comparison individually. The effects of graphite loading and drying method on the dispersion of graphite and the resultant properties of the composites such as electrical and thermal conductivity, friction, and dynamic mechanical properties were studied. The results from transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X‐ray diffraction showed that the composites prepared by fast spray drying exhibited a higher degree of exfoliation and a better dispersion of graphite sheets in the PVP matrix than the corresponding composites prepared by direct drying, leading to a conclusion that fast spray drying can effectively prevent from re‐stacking of the exfoliated graphite sheets as illustrated. As a result, dynamic mechanical thermal analysis showed significant increases in the storage modulus and glass transition temperature for the composites prepared by spray drying. Besides, the spray drying as well greatly improved the electrical and thermal conductivity of the composites. It was also found that the electrical and thermal conductivity of the composites strongly depended on the graphite dispersion, while the friction coefficient unexpectedly does not. Increasing graphite loading level might enhance the probability of graphite sheets re‐stacking, resulting in poor graphite dispersion. Copyright © 2011 John Wiley & Sons, Ltd.     

Atomistic simulations to compute surface properties of poly(N-vinyl-2-pyrrolidone) (PVP) and blends of PVP/chitosan

Atomistic simulations were performed on poly(N-vinyl-2-pyrrolidone) (PVP) and its blends with chitosan (CS) in different ratios using molecular mechanics (MM) and molecular dynamics (MD) simulations in three-dimensionally periodic and effective two-dimensionally periodic condensed phases. Four independent microstructures were generated to analyze their surface properties. The calculated surface-energy values for PVP compared quite well with the experimental data reported in the literature. The density profile was analyzed, and the structure of the films showed an interior region of the bulk density. Various components of the energetic interactions (torsional, van der Waals, etc.) were examined to gain deeper insight into the nature of regular and anomalous interactions between the bulk and the surface films. Surface energies of PVP/CS blends were computed by MD simulations using the bulk pressure-volume-temperature (PVT) parameters. Bulk properties such as the cohesive energy density (CED) and solubility parameter (delta) were calculated using MM and MD simulations in the NVT ensemble under periodic boundary conditions. The Flory equation of state was used to compute the thermal expansion coefficient as well as PVT parameters. These surface-energy values agreed well with the surface-energy data calculated using the Zisman equation, which were also in accordance with the experimental observations. The results from this study suggest that computer simulations would provide valuable information on polymers and polymer-blend surfaces.     

Effect of temperature on volumetric and transport properties of nanofluids containing ZnO nanoparticles poly(ethylene glycol) and water

The nanoparticles of ZnO have been dispersed in base fluids of poly(ethylene glycol), PEG, and its aqueous solutions. Stability of these nanofluids has been verified with UV-Vis spectroscopy. Dynamic light scattering and size analyze laser methods were used to obtain particle size of the nanofluids investigated. The density, speed of sound and viscosity values for these nanofluids have been measured at T = (293.15, 298.15, 308.15 and 318.15) K. From these experimental data, the excess molar volume, $V_m^E$ and isentropic compressibility, κ_s, have been determined. The behaviour of these values with temperature and concentration has been interpreted for clarifying the dispersion of ZnO nanoparticles in PEG and aqueous solution of PEG. The effects of ZnO nanoparticles and temperature have also been investigated on volumetric and transport properties of aqueous solutions of PEG. The $V_m^E$, was adequately fitted to the Redlich–Kister, Ott et al. and Singh et al. equations. The isentropic compressibility values were correlated with the polynomial equation. The Eyring-NRTL and Eyring-mNRF models have successfully been used for correlating the viscosity values of the nanofluids investigated with temperature dependency considered. The performance of the Einstein, Brinkman, Lundgren and Batchelor models in the prediction of viscosity values of the (ZnO + PEG) nanofluid has also been tested.     

Electrochemical synthesis of metal and semimetal nanotube-nanowire heterojunctions and their electronic transport properties

Metal and semimetal nanotube-nanowire heterojunction arrays have been achieved by sequential electrochemical-deposition inside the nanochannels of anodic aluminium oxide template with a layer of Au thin enough to leave the pores open.     

Linear silver clusters in aqueous solution (clusterites): radiation-induced chemical synthesis and properties

The formation and properties of the products of the radiation-induced chemical reduction of silver ions in aqueous solutions containing sodium polyacrylate were investigated. The absorption spectra of these species exhibit a band at 290 mn and a band in the visible region. The latter shifts from 470 nm to -800 nm with time or after the addition of silver ions. The species obtained (clusterites) arc linear silver clusters bound to the carboxyl groups of the ion exchanger. The red shift of the visible band is due to the increase in their size. The mechanism of the formation and the structure of the clusterites are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1429–1435, June, 1996.     

Oligo(U-terpyridines) and their ruthenium(II) complexes: synthesis and structural properties

A highly efficient domino reaction starting from tetrahydroquinolinone and a series of bisiminium salts provides the corresponding bis(U-terpyridines). These ligands have been treated with [(tpy)RuCl3] to afford novel dinuclear complexes [(tpy)Ru(L)Ru(tpy)]4+. The protocol is also applied for the synthesis of a star-shaped tris(U-terpyridine) and the trinuclear complex [{(tpy)Ru}3(L)]6+. In view of potential applications in the fields of metallopolymers and molecular devices, the electronic spectra, as well as the electrochemical potentials of all the complexes have been obtained. According to these data, no significant intermetal interaction has been observed for the ruthenium complexes presented here.     

Citrate-assisted synthesis of prickly nickel microwires and their surface modification with silver

A new type of prickly nickel microwires assembled by thornlike nanocrystals was fabricated through a simple chemical reduction route with the assistance of citrate. Thus-prepared nickel wires were subsequently morphology-retained modified with a thin silver shell via transmetallation. Compared with the uncoated sample, the Ni(core)-Ag(shell) wires exhibited much-enhanced oxidation resistance, slightly changed magnetic properties and stark different catalysis for the creation of carbon particles in pyrolyzing acetone.     

Experimental analysis of heat transfer behavior of silver,MWCNT and hybrid (silver +MWCNT) nanofluids in a laminar tubular flow

Journal of Thermal Analysis and Calorimetry - Experimental investigations were carried out in order to study the heat transfer performance of silver (Ag), multiwalled carbon nanotubes (MWCNT) and...