Increasing Silver Content Research Articles

Antibacterial, mechanical and surface properties of Ag-DLC films prepared by dual PLD for medical applications

Silver doped diamond-like carbon layers were deposited by dual pulsed laser deposition using two KrF excimer lasers. The concentration of Ag, determined by XPS and WDS, moved from zero to ~10at%. We found that the sp2/sp3 ratio, film roughness and the number of droplets (SEM and AFM) increased with increasing silver concentration. The sp3 content measurement (XPS) was influenced by ion cluster surface sputtering and varied from 71.0% (undoped DLC) to 36.2% (for 9.3at% Ag). Transmission was measured on the scale from 200nm to 1100nm, and decreased with increasing silver content. An increase of Ag content has an effect on the decrease of the storage modulus (E′) and the indentation hardness (HIT). The highest values HIT=51.9GPa and E′=270.6GPa were measured on a sample with 0at% Ag. The lowest values HIT=26.0GPa and E′=180.2GPa were measured on a sample of 9.3at% Ag. Film adhesion was studied using the scratch test and was up to 20.8N for the highest Ag concentration. The contact angle (CA) measurements for water showed that the CA of Ag-DLC films was higher (78°-98°) that of DLC film (77°). The surface free energy of DLC and of Ag-DLC was about 40mJ·m−2. Antibacterial properties were studied using gram positive and gram negative bacteria. The antibacterial effects increased with the Ag concentration and were ~99.9% after 24h for the layers with the highest silver content (9.3at%). Our results demonstrate that the Ag-doped DLC films are potentially useful biomaterials having both good mechanical properties and antimicrobial characteristics. Prime novelty statementUnique manufacturing technique dual pulsed laser deposition was applied on hydrogen-free diamond-like carbon doped by Ag including topological, physical and antibacterial characterization.

Investigation of rheological, structural, surface, optical and thermal properties of low temperature produced silver doped ZnO thick film as thermal interface material in lighting application

Effects of screen-printed AgxZn1−xO thick film deposited on Al substrate with composition 3 wt% ≤ x ≤ 9 wt% on the rheological, surface, vibrational and thermal properties were investigated in this paper. AgxZn1−xO powder with different doping concentration was synthesized through co-precipitation method and further mixed with solvent to form a thixotropic paste. The paste was screen-printed on Al substrate. Rheological behavior of pastes showed shear thinning phenomenon with increment of shear rate. Structural properties of pure and doped thick films were investigated by X-ray diffraction (XRD). It showed that (101) was a strong preferred orientation among other peaks. Field emission scanning electron microscopy (FESEM) results indicated the aggregated flake-like structure that become more prominent with increase of doping from 3 to 7 wt%. Surface roughness of the films exhibited a decreasing trend with the increase of silver content whereas the step analysis facilitated to identify the contact surface point of the film for thermal conduction in application purposes. By increasing the dopant’s concentration, peak position of ZnO had shifted within the range from 503 to 506 cm−1. FTIR spectra of the films showed no vibrational peaks related to AgO or Ag2O. Thermal characterization revealed a decreasing trend of film’s resistivity when the doping was increased to 7 wt%. The lowest achieved junction temperature with tested LED was measured at 47.32 °C at 7 wt% of silver doping.

Physicochemical and antimicrobial properties of silver‐doped hydroxyapatite collagen biocomposite

Silver‐doped hydroxyapatite (AgHAp) was prepared by co‐precipitation method at room temperature. The obtained AgHAp was added in different amounts of collagen gel (AgHApC1 and AgHApC2). Afterward, the gel was lyophilized and the final AgHApC1 and AgHApC2 composite was achieved. The purity, crystallinity, and the phase composition of the AgHAp, AgHApC1, and AgHApC2 samples were evaluated by X‐ray diffraction (XRD). The planes corresponding to the 2θ values for hydroxyapatite were found in the three samples analyzed in agreement with the crystalline hydroxyapatite. In the Fourier transform infrared (FT‐IR) spectra of AgHApC1 and AgHApC2 samples the peak characteristic to the presence of ν2 phosphate mode at 472/cm was found. The peaks resulting from the ν4 vibration of the P–O mode, ν1 symmetric P–O stretching vibration and ν3 P–O stretching vibration of were also evidenced in all the samples. The formation of agglomerated particles with uniform particle size was evidenced by scanning electron microscope (SEM). The uniform distribution of the constituent elements was evidenced by mapping analysis. Furthermore, the strong antibacterial activity of AgHAp, AgHApC1, and AgHApC2 samples against Gram‐negative (Escherichia coli) and Gram‐positive (Staphylococcus aureus) bacterial strains was shown. The inhibition zone increased drastically with the increase of silver concentration. POLYM. ENG. SCI., 57:537–545, 2017. © 2017 Society of Plastics Engineers

Effect of silver doping on optical properties of nanoflower ZnO thin films prepared by spray pyrolysis technique

Silver doped zinc oxide (ZnO) thin films have been synthesized by spray pyrolysis method on the substrate at a temperature of 450 °C. The aqueous Zinc acetylacetonate (ZnC10H14O5) and silver nitrate (AgNO3) dissolved in ethanol were used as a starting material. The effect of sliver doping on the structural, surface morphological, electrical as well as optical properties of Ag: Zno thin films were studied. It is confirmed by the X-ray diffractogram that the Ag: ZnO thin films was polycrystalline nature with the preferential orientation along (002) plane in wurtzite structure. The Scanning Electron Microscope exhibited the surface formation of nanoflower shaped grains with an addition of silver (Ag) and compositional analysis by Energy Dispersive Spectroscopy confirmed the presence of Zinc (Zn), Oxigen (O) and silver (Ag). Atomic force microscopy revealed that surface roughness of the films was decreased with the increase of silver concentration. The films were found to exhibit high transmittance and low absorbance in the visible /new infrared region.

Synthesis and Characterization of Ag-Modified V2O5Photocatalytic Materials

V2O5powders modified with different theoretical silver contents (1, 5, 10, 15, and 20 wt% as Ag2O) were obtained with acicular morphologies observed by scanning electron microscopy (SEM). Shcherbinaite crystalline phase is transformed into the Ag0.33V2O5crystalline one with the incorporation and increase in silver content as was suggested by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. With further increase in silver contents the Ag2O phase appears. Catalysts were active in photocatalytic degradation of malachite green dye under simulated solar light, which is one of the most remarkable facts of this work. It was found that V2O5-20Ag was the most active catalytic formulation and its activity was attributed to the mixture of coupled semiconductors that promotes the slight decrease in the rate of the electron-hole pair recombination.

Composition-dependent electronic energy relaxation dynamics of metal domains as revealed by bimetallic Au144-xAgx(SC8H9)60 monolayer-protected clusters.

We examined the electronic relaxation dynamics for mono and bimetallic Au144-xAgx(SC8H9)60 monolayer-protected clusters (MPCs) using femtosecond time-resolved transient extinction spectroscopy. MPCs provide compositionally well-defined model systems for structure-specific determination of nanoscale electronic properties. Based on pulse-energy-dependent transient extinction data, we quantified electron-phonon coupling constants for three distinct Au144-xAgx(SC8H9)60 MPC samples, where x = 0, 0 < x < 30, and x ∼ 30, as Gx=0 = (1.61 ± 0.1) × 1016 W m-3 K-1, Gx<30 = (1.74 ± 0.1) × 1016 W m-3 K-1 and Gx∼30 = (2.07 ± 0.15) × 1016 W m-3 K-1, respectively. These results reflect a trend of greater electron-phonon coupling efficiency with increasing silver content. Based on these data, we conclude that gold-atom replacement by silver occurs at surface sites of the 114-atom metal core of the MPC. Definitive determinations of functional response to nanoscale "alloy" formation and dopant inclusion are critical to establishing predictive models for the development of materials that feature nanoparticles as active components.

Electron thermal EMF for NaxCu2-xS

In the present study, the temperature dependences of the thermoelectromotive force (thermo–emf) in copper selenide, substituted in a small concentration, were studied. The results of the measurements showed that the thermo–emf coefficient of the samples increases, and the conductivity decreases with increasing silver concentration in its composition. These results allow – with optimal selection of the doping regime and protective coatings – to develop on the basis of nanostructured copper selenide an effective thermoelectric for use at temperatures of 20–500°C as p–type semiconductors suitable for increasing the efficiency of thermoelectric generators.

Influence of silver content on rifampicin adsorptivity for magnetite/Ag/rifampicin nanoparticles

Magnetite nanoparticles (NPs) decorated with silver (magnetite/Ag) are intensively investigated due to their application in the biomedical field. We demonstrate that the increase of silver content on the surface of nanoparticles improves the adsorptivity of antibiotic rifampicin as well as antibacterial properties. The use of ginger extract allowed to improve the silver nucleation on the magnetite surface that resulted in an increase of silver content. Physicochemical and functional characterization of magnetite/Ag NPs was performed. Our results show that 5%–10% of silver content in magnetite/Ag NPs is already sufficient for antimicrobial properties against Streptococcus salivarius and Staphylococcus aureus. The rifampicin molecules on the magnetite/Ag NPs surface made the spectrum of antimicrobial activity wider. Cytotoxicity evaluation of the magnetite/Ag/rifampicin NPs showed no harmful action towards normal human fibroblasts, whereas the effect on human embryonic kidney cell viability was time and dose dependent.

Microstructure and properties of VN/Ag composite films with various silver content

The VN/Ag composite films with various silver content were prepared by PLD technique, and the microstructures, mechanical and tribological properties at elevated temperature to 900 °C of films were investigated, respectively. The results show that the films were composed of the fcc VN and Ag nano-crystalline grains. With the increase of silver content from 8.2 to 56.1 at.%, the grain size increased and the surface morphology deteriorated gradually, the hardness and elastic modulus of the films decreased from 18.6 GPa, 226.3 GPa–8.1 GPa, 126.6 GPa, respectively. Only appropriate silver addition could improve the lubricity of the VN/Ag films. The film with 16.6 at.% Ag were found to be optimized for lubrication from RT to 900 °C. At low temperatures, the lubricant property of the film relied on the metal silver heavily. At elevated temperatures, a series of Magnéli phase (vanadium oxides) and the layered structure silver vanadates (such as Ag3VO4, AgVO3) formed by tribochemical reactions in the contact area played a critical role in improving lubrication properties. A synergy of the lubricating Ag at low temperatures and the new lubrication phases generated at high temperatures could be responsible to the excellent lubricity of the VN/Ag films in wide temperature range.

The optical, photo catalytic behavior and hydrophilic properties of silver and tin co doped TiO2 thin films using sol–gel method

Ag and Sn co doped TiO2 thin films were deposited on glass slides by sol–gel dip coating technique. Morphology, optical properties and wettability of the obtained TiO2 thin films changed by changing the content of dopant. The TiO2 thin films with silver molar ratio from 5 to 20% (molar ratio of tin fixed at 5 mol%) were tested for its photo catalytic property under irradiation of visible light. The influences of different molar ratio of Ag on hydrophilicity of the films were also investigated by measuring the water contact angle. The results showed that the wettability was significantly improved by increasing silver content comparing with pure TiO2 thin film. Accordingly, the thin films showed various optical band gaps. As, the optical band gap of the nanostructured thin films decreased with various content of dopant from 3.15 to 2.13 eV.

Characterization of casein and casein-silver conjugated nanoparticle containing multifunctional (pectin-sodium alginate/casein) bilayer film.

Casein nano particles and casein-silver conjugated nano composite containing edible bilayer pouch was developed from a heat sealable casein layer laminated with sodium alginate-pectin layer. The physicochemical, mechanical, biodegradability and the toxicity of the film were evaluated. The synthesized casein nano particle was incorporated in the casein layer (inner layer) of the film, however, the casein-silver conjugated nano composite were incorporated in the sodium alginate-pectin (outer) layer of the film. The mechanical, barrier, physical and antimicrobial properties of the film were investigated. Addition of nano composite/nano particle reduced the water solubility (from 67 to 46% at 80°C temperature) of the film improved the water barrier properties, light barrier properties, tensile strength and thermal properties of the film. The light barrier properties of the film increased and transparency reduced with increase in silver content in the conjugated nano composite film. The nano particles/nano composite containing film showed antibacterial activity against E. coli. The films were recorded safe for red blood cells as % haemolysis for all the tested samples were found to be well below the safe level.

Effect of silver on the phase transition and wettability of titanium oxide films.

The effect of silver on the phase transition and microstructure of titanium oxide films grown by pulsed cathodic arc had been investigated by XRD, SEM and Raman spectroscopy. Following successive thermal annealing up to 1000 °C, microstructural analysis of annealed Ag-TiO2 films reveals that the incorporation of Ag nanoparticles strongly affects the transition temperature from the initial metastable amorphous phase to anatase and stable rutile phase. An increase of silver content into TiO2 matrix inhibits the amorphous to anatase phase transition, raising its temperature boundary and, simultaneously reduces the transition temperature to promote rutile structure at lower value of 600 °C. The results are interpreted in terms of the steric effects produced by agglomeration of Ag atoms into larger clusters following annealing which hinders diffusion of Ti and O ions for anatase formation and constrains the volume available for the anatase lattice, thus disrupting its structure to form rutile phase. The effect of silver on the optical and wetting properties of TiO2 was evaluated to demonstrate its improved photocatalytic performance.

Peculiarities of the dielectric response of the silver-modified-zeolite porous microstructure

The aim of this study was to characterize electrical conductivity and dielectrical properties of the silver-exchanged zeolite - natural clinoptilolite from Western part of Turkey and Azerbaijan in the range of frequencies from 200 Hz to 1 MHz and at room temperature. For a better understanding the effect of concentration and content of silver in the nanoporous zeolite volume on the conductivity, a study of the dielectric properties of an un-modified and silver-modified zeolite plates with different amounts of Ag ions and Ag nanoparticles is performed. Un-modified and three different types of the silver ion-exchanged modified clinoptilolite plates were prepared. It was found, that with increasing silver concentration, resistance of zeolite plate monotonically decreases at the same time a capacitance is increases. It is suggested an explanation of the observed frequency dependence of the capacitance and resistance of zeolite plates on the silver concentrations may be explain on the basis of an electrode-dielectric interface gap model. At the same time, the observed phenomenon can be explained by considering the fact that with increasing content of silver the conductivity increases. These results show that Ag nanoparticles play significant role for performance improvement in plasma electronic devices with zeolite cathode.

Silver fillers aspect ratio influence on electrical and thermal conductivity in PEEK/Ag nanocomposites

The development of polymer based conductive composites is required in aeronautical applications where electrostatic charges and heat need to be evacuated. Optimization of conductive filler content is necessary to maintain low density and high mechanical properties provided by the polymer matrix. We introduced silver nanoparticles in Polyetheretherketone. Electrical conductivity, specific heat capacity, thermal conductivity and thermal diffusivity have been determined as a function of filler content and temperature. In particular, we studied the influence of silver nanoparticles aspect ratio on these thermal properties. We compared nanospheres with nanowires. A low electrical percolation threshold (0.55vol%) is obtained for silver nanowires composites compared to spherical particles (10.8vol%). Thermal conductivity increases with silver content and the influence of filler aspect ratio is interesting: thanks to nanowires, the thermal conductivity enhancement is reached for lower silver content. Experimental data are well fitted with Nan model. Specific heat capacity decreases with the introduction of silver nanoparticles, following the mixture rule independently of aspect ratio. Composites thermal diffusivity also increases with increasing silver content and influence of filler aspect ratio can be brought to light. Temperature dependence of these thermal properties indicate a dominant heat transport mechanism typical of disordered materials.

Effect of Ag+ ion Concentration on the Reaction Kinetics and Shape of Nanoparticles Synthesised by Green Chemical Approach

The effect of varying Ag+ ion concentration on the green chemical reaction with a fixed tea aliquot concentration has been studied in detail with the help of UV-visible absorption spectra. With increase in the concentration of Ag+ solution the position of surface plasmon band systematically increased from 435 nm – 450 nm. The reaction followed first order kinetics and the rate of reaction increased in a linear fashion with k = 3.54 x 10-4 min-1 for 0.5 mL to k = 1.86 x 10-3 min-1 for 3.0 mL Ag+ solution. X-ray diffraction patterns showed an enhanced (200) reflection for 3.0 mL Ag sample. The shape of Ag nanoparticles could be effectively tuned from spherical to cuboid with increase in silver content as evidenced from scanning electron and transmission electron micrographs. The average particle size of Ag NPs increased from 25 nm to 55 nm with increase in the Ag+ content of the reaction.

Chronic effect of waterborne colloidal silver nanoparticles on plasma biochemistry and hematology of rainbow trout (Oncorhynchus mykiss)

Objective: To investigate the possible effects of silver nanoparticles (AgNPs) on some blood and plasma indices of rainbow trout (Oncorhynchus mykiss). Methods: Hence, fish were exposed for 21 days to sub-lethal concentrations of colloidal AgNPs and blood parameters including erythrocyte size and hematocrit, plasma parameters including cholinesterase, cortisol, sodium, chloride, and potassium, and also silver concentration in plasma were measured following the 11th and 21st days of exposure. Results: According to the results of present study, higher concentrations of AgNPs had more significant effects on plasma biochemistry and hematology of trout. The greatest impacts were decline of chloride ions and increase of cortisol and cholinesterase. Also fish exposed to AgNPs significantly increased silver concentration in the plasma. Conclusions: Further studies are needed to identify appropriate blood biomarkers following fish exposed to nanomaterials, especially AgNPs. Article history:

Antibacterial activity of graphene supported FeAg bimetallic nanocomposites

We report the simple one pot synthesis of iron-silver (FeAg) bimetallic nanoparticles with different compositions on graphene support. The nanoparticles are well dispersed on the graphene sheet as revealed by the TEM, XRD, and Raman spectra. The antibacterial activity of graphene-FeAg nanocomposite (NC) towards Bacillus subtilis, Escherichia coli, and Staphylococcus aureus was investigated by colony counting method. Graphene-FeAg NC demonstrates excellent antibacterial activity as compared to FeAg bimetallic without graphene. To understand the antibacterial mechanism of the NC, oxidative stress caused by reactive oxygen species (ROS) and the glutathione (GSH) oxidation were investigated in the system. It has been observed that ROS production and GSH oxidation are concentration dependent while the increase in silver content up to 50% generally enhances the ROS production while ROS decreases on further increase in silver content. Graphene loaded FeAg NC demonstrates higher GSH oxidation capacity than bare FeAg bimetallic nanocomposite. The mechanism study suggests that the antibacterial activity is probably due to membrane and oxidative stress produced by the nanocomposites. The possible antibacterial pathway mainly includes the non-ROS oxidative stress (GSH oxidation) while ROS play minor role.

Surface characterization and biological evaluation of silver-incorporated DLC coatings fabricated by hybrid RF PACVD/MS method

Since the biological response of the body towards an implanted material is mainly governed by its surface properties, biomaterials are improved by various kinds of coatings. Their role is to provide good mechanical and biological characteristics, and exclude some disadvantages like post-implantation infections. This phenomenon may be reduced by introduction of silver as an antibacterial agent. This study evaluates the Ag-DLC films synthesized by the hybrid RF PACVD/MS method according to the patent number PL401955-A1 worked out inter alia by the authors. Such tests as XPS, SEM, EDS, AFM, FTIR, Raman and ICP-TOF-MS were used to determine surface properties of the coatings. The obtained results were correlated with the biological response estimated on the basis of cells viability assay (osteoblast cells line Saos-2) and bacterial colonization test (Escherichia coli strain DH5α). Results showed that the hybrid RF PACVD/MS method allows one to get tight coating preventing the diffusion of harmful elements from the metallic substrate. Ag concentration increases with the growing power density, it occurs in metallic state, does not create chemical bonds and is evenly dispersed within the DLC matrix in the form of nanoscale silver clusters. Increasing silver content above 2at.% improves bactericidal properties, but decreases cell viability

Effects of multiple hydrogen absorption/desorption cycles on the mechanical properties of the alloy system palladium/silver (wt% = 10–25)

Changes to the strength, hardness and ductility of a series of well-annealed palladium–silver alloys have been investigated as a function of the number of isothermal hydrogen absorption/desorption cycles the annealed alloy specimens were subjected to. The results indicate that the overwhelming majority of the changes to the mechanical properties occur as a result of the first hydrogen exposure treatment. The degree of change to the mechanical properties of the alloys has been found to be dependent on the silver content of each alloy, decreasing as the silver content increases.

Nano structured CdO films grown by the SILAR method: Influence of silver-doping on the morphological, structural and optical properties

Cadmium oxide films with and without silver-doping have been prepared by the SILAR method onto soda-lime-silica glass slides and characterized by scanning electron microscopy, UV-Visible spectroscopy and X-ray diffraction measurements. Scanning electron microscopy images show that increasing silver concentration contributed to adjust surface properties and led to a decrease in particle size from the UV-Visible spectroscopy analysis it was found that the optical band gap value of the films is increased with silver doping.