Adding Silver Nanoparticles Research Articles

Antimicrobial activity and properties of irreversible hydrocolloid impression materials incorporated with silver nanoparticles

Statement of problemConventional spray and the immersion disinfection of irreversible hydrocolloid impression materials may lead to dimensional changes. PurposeThe purpose of this in vitro study was to investigate the antimicrobial activity and properties of irreversible hydrocolloid impression materials incorporated with silver nanoparticles. Materials and methodsThe antimicrobial activity and properties of 2 commercially available irreversible hydrocolloid impression materials were evaluated after incorporating varying concentrations of silver nanoparticles. Antimicrobial activity was determined using the disk diffusion method. The gel strength, permanent deformation, flow, and gelation time were measured according to American Dental Association specification #18. Analysis of variance was used to identify the significant differences within and across the groups (α=.05). ResultsAdding silver nanoparticles to irreversible hydrocolloid impression materials resulted in superior antimicrobial activity without adversely affecting their properties. Adding silver nanoparticles to Zelgan significantly increased the gel strength compared with the control group, except at 5 wt%. However, the gel strength of Tropicalgin was unaffected except at 5 wt%. An increase in the permanent deformation was found with the incorporation of silver nanoparticles in both Zelgan and Tropicalgin. The flow of Zelgan increased with the incorporation of silver nanoparticles, whereas a decrease in the flow of Tropicalgin was observed at 1 wt% and 2 wt%. An increase in the gelation time of both Zelgan and Tropicalgin was observed with the incorporation of silver nanoparticles. ConclusionsBased on this in vitro study, silver nanoparticles can be incorporated into irreversible hydrocolloid impression materials as antimicrobial agents without adversely affecting their properties.

Concept and Nanostructure Control of Plasmonic Porous Silicon Solar Cells

[Introduction]A multi-junction solar cell can generate high open current voltage by each layer absorbing a different wavelength light, although lattice mismatch between materials is one of its problems. A possible new type of solar cell is an all-Si tandem solar cell, which will have no mismatch. Our laboratory noticed that porous silicon is a light-absorbing material for short wavelengths. Its nano-scale holes on its surface increases its band gap due to the quantum size effect. Because this porous structure, however, leads to high resistivity and low absorption coefficient, the porous layer must be made thinner by enhancing light absorption. To improve light absorption, we propose using localized surface plasmon of metal nanoparticles [1, 2]. By such introduction of these particles into the holes of porous silicon, a thinner porous layer can be also achieved. Here, we proposed this plasmonic porous silicon solar cell (or PPSSC), and aimed to control the structure of porous silicon. To determine guidelines for fabricating PPSSCs, we created solar cells consisting of porous silicon, and then measured their I-Vcharacteristics. By simulation, we estimated the enhancement of light absorption of porous silicon with metal nanoparticles. [Experimental]1. Preparation of porous silicon: Here, p-type monocrystalline silicon wafers with three different resistivities were anodized for different times and current density. The surfaces and cross-sections were then observed by field emission scanning electron microscopy (FE-SEM) and evaluated using UV-vis spectrum. Several wafers were also treated with Ar dry etching, and its effect on their surface structure observed. 2. Fabrication of solar cells: An n-type silicon layer was deposited on top of the porous silicon by chemical vapor deposition (CVD) using SiH4 and PH3 in H2. Silver electrodes were fabricated using RF sputtering, and then their rectification property and quantum efficiency were measured. 3. FDTD simulation: With the Finite-Different-Time-Domain (FDTD) method, we created a simulation model in which silver nanoparticles exist in the holes on the silicon surface. The simulation showed how the light absorption in this combined material is enhanced by adding silver nanoparticles to the porous silicon. Then, the necessary layer thickness of porous layer was estimated by the model, and the influence of localized surface plasmon was verified by investigating the strength of the electrical field near the interface between the silicon and silver nanoparticles. [Results and Discussion] 1.Structure control of porous silicon: By changing the anodization time and current density, we successfully fabricated porous silicon of various pore size, depth, and porosity. Figure 1 shows the relationship between current density I and pore diameter. In addition, results reveal that dry etching expands the pore size of a porous silicon surface (Fig. 2), indicating that dry etching might facilitate both the introduction of metal nanoparticles and the control of band gaps. 2.Evaluation of porous silicon solar cells: Figure 3 shows that a thin n-type silicon layer was successfully deposited on the porous silicon by CVD. Figure 4 shows that p-n junctions were also formed by this deposition. However, compared with a monocrystalline silicon solar cell (Fig.5), porous silicon solar cells tended to have a smaller increase rate of I than that of V. One factor in this trend is the high resistivity of porous silicon, indicating that making the porous silicon layer thinner is important to increase the efficiency of PPSSCs. Figure 6 compares the quantum efficiency of porous silicon and monocrystalline silicon solar cells, revealing that porous silicon solar cells have lower quantum efficiency. One explanation is that insufficient deposition of n-type silicon onto the porous silicon accelerates surface recombination. This surface recombination can be improved by performing passivation. 3.Evaluation of combined materials by simulation: FDTD simulation indicated that the light absorption of the combined materials can be improved when the silver nanoparticles exist in the holes of porous silicon, and that a strong electrical field is injected into the silicon around the interface between silicon and the silver nanoparticles. These results indicate that localized surface plasmon might improve light absorption and enhance thinner porous silicon as a light absorption layer. [Conclusion] Current density, resistivity of wafers, and dry etching can be factors in controlling the structure of porous silicon. We successfully formed p-n junctions with porous silicon, and based on the measured I-Vcharacteristics and quantum efficiency of porous silicon solar cells, the porous silicon needs to be thinner and needs passivation. The simulations suggest that metal nanoparticles enhance the light absorption.

Effect of silver nanoparticles on the performance of riverbank filtration: Column study

Soil column experiments were evaluated effects of silver nanoparticles (i.e., 0, 2.5, 5, and 10 mg/L) on the microbial viability which is strongly associated with the degradation of organic matter, pharmaceutically active compounds(PhACs) and biological oxidation of nitrogenous compounds during river bank filtration. The addition of silver nanoparticles resulted in almost no change in the aqueous matrix. However, the intact cell concentration decreased with addition of silver nanoparticles from 2.5 to 10 mg/L, which accounted for 76% to 82% reduction compared to that of control (silver nanoparticles free surface water). The decrease in adenosine triphosphate was more pronounced; thus, the number and active cells in aqueous phase were concurrently decreased with added silver nanoparticles. Based on the florescence excitation-emission matrix and liquid chromatograph - organic carbon detection analyses, it shows that the removal of protein-like substances was relatively higher than that of humic-like substances, and polysaccharide was substantially reduced. But the extent of those substances removed during soil passage was decreased with the increasing concentration of silver nanoparticles. The attenuation of ionic PhACs ranged from 55% to 80%, depending on the concentration of silver nanoparticles. The attenuation of neutral PhACs ranged between 72% and 77%, which was relatively lower than that observed for the ionic PhACs. The microbial viability was affected by silver nanoparticles, which also resulted in inhibition of nitrifiers.

Kinetic evaluation study on the bioactivity of silver doped hydroxyapatite-polyvinyl alcohol nanocomposites

This work investigates the effect of adding silver nanoparticles (NPs) in ppm on the bioactivity of hydroxyapatite/polyvinyl alcohol nanocomposites (HAV). HAV prepared by an in situ biomimetic approach was doped with different concentrations of silver NPs (HAV-Ag), and the formed powder samples were characterized by different techniques such as Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-EOS), X-ray diffraction, transmission electron microscope, and Fourier Transform Infrared Spectroscopy. Bioactivity was evaluated in simulated body fluid through studying the kinetics of Ca and P uptake onto the different HAV-Ag nanocomposites. Uptake profiles of Ca and P were well described by a pseudo-second order kinetic model, and the obtained kinetic parameters confirmed that the highest uptake capacities were achieved by adding less than 0.001 ppm of silver NPs which is an amount not detectable by ICP. Furthermore, HAV-Ag nanocomposites were shown to be non-toxic as well as have a strong antibacterial effect. Silver NPs significantly enhanced the bioactivity of HAV nanocomposites and thus the developed nanocomposites promise to be excellent biomaterials for bone and reconstructive surgery applications.

In Vitro Comparison of Compressive and Tensile Strengths ofAcrylic Resins Reinforced by Silver Nanoparticles at 2% and0.2% Concentrations.

Background and aims. Polymethyl methacrylate, PMMA, is widely used in prosthodontics for fabrication of removable prostheses. This study was undertaken to investigate the effect of adding silver nanoparticles (AgNPs) to PMMA at 2% and 0.2% concentrations on compressive and tensile strengths of PMMA.Materials and methods. The silver nanoparticles were mixed with heat-cured acrylic resin in an amalgamator in two groups at 0.2 and 2 wt% of AgNPs. Eighteen 2×20×200-mm samples were prepared for tensile strength test, 12 samples containing silver nanoparticle and 6 samples for the control group. Another 18 cylindrical 25×38-mm samples were prepared for compressive strength test. Scanning electron microscopy was used to verify homogeneous distribution of particles. The powder was manually mixed with a resin monomer and then the mixture was properly blended. Before curing, the paste was packed into steel molds. After curing, the specimens were removed from the molds. One-way ANOVA was used for statistical analysis, followed by multiple comparison test (Scheffé’s test).Results. This study showed that the mean compressive strength of PMMA reinforced with AgNPs was significantly higher than that of the unmodified PMMA (P<0.05). It was not statistically different between the two groups reinforced with AgNPs. The tensile strength was not significantly different between the 0.2% group and unmodified PMMA and it de-creased significantly after incorporation of 2% AgNPs (P<0.05).Conclusion. Based on the results and the desirable effect of nanoparticles of silver on improvement of compressive strength of PMMA, use of this material with proper concentration in the palatal area of maxillary acrylic resin dentures is recommended.

Antimicrobial Efficacy of Mineral Trioxide Aggregate with and without Silver Nanoparticles.

Most current root-end filling materials do not provide a perfect seal. Thus, a microscopic space is likely to exist in the interface between walls of the root-end cavity and filling material, which allows microorganisms and their products to penetrate. In addition to good sealing ability and biocompatibility, root-end filling materials should ideally have some antimicrobial activity. Therefore, this in vitro study aimed to evaluate the antimicrobial properties of Angelus white mineral trioxide aggregate (MTA) and the mixture of MTA with silver nanoparticles (1% weight; MTA/SN). Antimicrobial properties of MTA and MTA/SN were tested by agar diffusion technique against Enterococcus faecalis, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans. The microbial inhibition zones around the materials were measured by a caliper with 0.1-mm accuracy. Student's t-test was used for comparison between the two groups in normal data distribution and Man-Whitney U test for non-normal distribution. Student's t-test revealed that for E. faecalis, C. albicans, and P. aeruginosa, microbial inhibition zone of MTA/SN was significantly greater than that of MTA (P = 0.000). Mann-Whitney U test indicated no significant difference between the effect of MTA and MTA/SN on S. aureus (P > 0.05). Based on the results of this study, adding silver nanoparticles to MTA improved its antimicrobial efficacy.

Effects of adding silver nanoparticles on the toughening of dental porcelain

Dental porcelains currently used for ceramic restorations are brittle, and it is sometimes necessary to replace fractured or chipped restorations. Porcelain is fragile and exhibits elastic deformation rather than plastic deformation, leading to fracture or chipping of restorations. The purpose of this study was to investigate the toughening of porcelain through the addition of silver nanoparticles. Noritake Super (NS) Porcelain AAA modified with the addition of silver nanoparticles was used. The concentration of silver in the solution was adjusted to 100, 200, 500, and 1000 ppm (Ag100, Ag200, Ag500, and Ag1000). The Vickers hardness (Hv) and median crack length extending from the corner of each indent were measured. The fracture toughness (KIC) was calculated by the indentation method. Optical reflectance spectra were recorded by using a spectrometer in the wavelength range of 200 to 700 nm. X-ray diffraction spectroscopy, color measurement, Fourier transform infrared spectroscopy, and electron probe microanalysis were also performed. The observed values of Hv, 2a, E, and KIC were compared and evaluated with a 1-way ANOVA, followed by the Bonferroni method (α=.05). The addition of silver nanoparticles significantly increased the Hv of all specimens with the exception of Ag100. The median crack length was significantly smaller in Ag500 (104.5 μm, SD: 11.9) and Ag1000 (100.0 µm, SD: 5.5). Significantly higher toughness values were observed for Ag500 (1.54 MPa·m(1/2), SD: 0.05) and Ag1000 (1.51 MPa·m(1/2), SD: 0.08) than for the control (1.36 MPa·m(1/2), SD: 0.03). In terms of color difference, Ag500 (5.08, SD:1.32) and Ag1000 (5.47, SD:1.05) had values significantly greater than ΔE*=2.69. The addition of silver nanoparticles significantly increased the fracture toughness and Vickers hardness of the NS porcelain. A residual compressive stress was generated due to the ion exchange reaction and differential thermal expansion of the silver metal nanoparticles. However, the addition of Ag500 and Ag1000 nanoparticles led to a color change.

Boiling local heat transfer enhancement in minichannels using nanofluids

This paper reports an experimental study on nanofluid convective boiling heat transfer in parallel rectangular minichannels of 800 μm hydraulic diameter. Experiments are conducted with pure water and silver nanoparticles suspended in water base fluid. Two small volume fractions of silver nanoparticles suspended in water are tested: 0.000237% and 0.000475%. The experimental results show that the local heat transfer coefficient, local heat flux, and local wall temperature are affected by silver nanoparticle concentration in water base fluid. In addition, different correlations established for boiling flow heat transfer in minichannels or macrochannels are evaluated. It is found that the correlation of Kandlikar and Balasubramanian is the closest to the water boiling heat transfer results. The boiling local heat transfer enhancement by adding silver nanoparticles in base fluid is not uniform along the channel flow. Better performances and highest effect of nanoparticle concentration on the heat transfer are obtained at the minichannels entrance.

Improving the Performance of a Zinc Oxide Nanowire Ultraviolet Photodetector by Adding Silver Nanoparticles

A significant enhancement in the performance of a ZnO nanowire-based UV detector has been achieved through fabricating a Ag/ZnO heterostructure by a photoreduction reaction. This enhancement is due to a Schottky barrier at the interface of Ag and ZnO because of the formation of a thin AgOx layer. An efficient and low-working-temperature method was proposed for eliminating the familiar persistent photoconductivity in ZnO nanostructure-based photodetectors, and the approach can be widely applied to other photodetectors employing the Schottky barrier phenomenon.

Silver nanoparticles effect on the wettability of Sn‐Ag‐Cu solder pastes and solder joints microstructure on copper

PurposeThe purpose of this paper is to investigate the influence of silver nanoparticle additions on the wetting properties of Sn‐Ag‐Cu (SAC) solder paste. In this investigation, the basic solder paste contained 85 wt.% of commercial Sn 96.5 Ag 3 Cu 0.5 powder (with the particle sizes in the range of 20‐38 μm) and 15 wt.% of self‐prepared middle activated rosin flux. To this paste was added 0.5, 1, 2 and 4 wt.% of self‐prepared silver nano‐powders of different grain sizes (from 9 to 138 nm). After the pastes had stabilized, their wetting properties were tested. The main goal of these investigations was to improve the wetting properties of SAC solder paste and to find correlations between the results of the wetting of solder paste with nanoparticles on the copper substrate with the microstructure of the solder joints.Design/methodology/approachThe following methods were applied for the wetting solder paste investigation: spreading on the copper substrate, contact angle measurement on the copper and wetting on a FR‐4 laminate double sided with an 18‐μm thick copper foil. The investigations were performed at temperatures of 220, 230, 240 and 250°C. Cross‐sectioning was performed on the solder paste after reflow on the copper substrate. For the microstructural analysis of the “nano” modified solder joints obtained at 250°C, standard metallographic procedures were applied. Changes in the microstructure, the thickness of the inter‐metallic compounds (IMCs) and their chemical compositions were observed by means of scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS).FindingsAs expected, a higher silver nanoparticle addition to the SAC solder paste resulted in better wetting properties on copper. The results indicated the possibility of an improvement of the reflow soldering process by using SAC solder paste with silver nanoparticles and by lowering its soldering temperature. An improvement was also observed in the wettability with a decrease in the silver nanoparticle grain size. Also, the wettability proceeded at a lower temperature (20°C lower) than that for the SAC paste, without the nano‐additives. For the 4 per cent silver nanoparticle addition, Ag3Sn star‐like IMCs were also found, which grew with the lowering of the silver nanoparticle grain size.Research limitations/implicationsFurther studies are necessary for confirmation of the practical application, especially of the mechanical properties, as well as the reliability properties of the solder joints, for the chosen solder paste with silver nanoparticles.Practical implicationsTaking into account the wetting data, the best results of the “nano” SAC solder pastes were obtained for the highest addition of the silver nanoparticles. It was found that the spreading on copper was higher and the contact angles were lower for the SAC solder paste with 4 per cent (by wt.) of 138‐nm grain size silver nanoparticles. A comparison of SAC solder pastes with a 4 per cent silver nanoparticle addition but of a different grain size (138‐9 nm), suggested a further improvement in wetting properties with lowering of the silver nanoparticle grain size. The results suggested the possibility of an improvement in the reflow soldering process by using SAC solder paste with silver nanoparticles and by lowering its soldering temperature.Originality/valueSpreading, wetting and contact angle measurement methods were used for the wetting determination of the SAC solder paste with the silver nanoparticles on copper under the same temperature conditions. Also, the microstructure of the solder joints obtained at 250°C was determined with the use of SEM and EDS methods. The results obtained made it possible to draw conclusions regarding the correlation between the output of the wetting results and the amount and the grain size of the added silver nanoparticles, and also the microstructure and thickness of the IMCs of the “nano” solder joints.

Plasmonics for Light Trapping in Silicon Solar Cells

The cost of the wafer represents a significant share of the cost of a solar module. One way to reduce it is to reduce the wafer thickness. However, this leads to increases in the transmission of the sunlight through the cell. Therefore, light trapping schemes must be applied to the solar cell. In recent years, metallic nanoparticles have been shown to enhance absorption in a solar cell through surface plasmon-related e_ects. In the present work, a method of producing silver nanoparticles has been investigated; evaporation of silver followed by annealing. Electron microscopy was used to determine how particle size and shape depends on process conditions. Process parameters like deposited silver thickness and time and temperature of the annealing step were investigated. The change in reflection when adding silver nanoparticles on the silicon wafers was measured.

Effect of Lead-Free Frit on Conductivity of Nanoparticles-Aided Silver Paste

Silver thick films were prepared from lead-free silver paste adding silver nanoparticles for low sintering temperature, and the effect of glass frit content on conductivity in the films was investigated. Silver pastes with different glass contents were prepared by mixing micron-scale silver powder of 1.6 microm and nanoparticles of 30-50 nm in size. To prepare lead-free silver paste, 5 wt% of the silver nanoparticles as a sintering aid were added to the micron-scale silver powder. Then, 3 wt%, 6 wt%, and 9 wt% of lead-free frits were added to the mixed powders. Using the paste, thick films were prepared by a screen printing on an alumina substrate and then the films were sintered at temperatures from 300 degrees C to 550 degrees C. As increasing the sintering temperature and content of lead-free frit, the thick films showed dense microstructure. The glass frit enhanced to develop denser microstructure by liquid phase sintering. However, excess of glass content increased sheet resistivity due to the formation of glass pool separated from particle network. Furthermore, the nanoparticles can assist to develop a conductive network in the film. The films with 6 wt% of glass frit had the best conductive network and the lowest sheet resistivity of 3.2 microomega cm.

Study on the nano-composite electroless coating of Ni–P/Ag

The nano-composite coating of Ni–P/Ag was obtained by adding silver nanoparticles to the Ni–P electroless plating solutions. The properties of the coating were tested by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), differential scanning calorimeter (DSC), X-ray diffraction (XRD) and microsclerometer. Silver nanoparticles changed the properties of the composite coating. The Ni–P electroless coating contains 12.23 wt.% P while the composite coating of Ni–P/Ag contains 11.17 wt.% P and 0.24 wt.% Ag. The hardness of the composite coating is bigger than that of Ni–P alloy coating. Differential scanning calorimeter studies showed the amorphous to crystalline transition with precipitation of Ni 3P and Ni around 335 °C.

Tuning luminescence intensity of RHO6G dye using silver nanoparticles

The photoluminescence (PL) from rhodamine (RHO6G) dye dispersed in ethanol has been studied in the presence of different amounts of citrate stabilized silver nanoparticles of size, ∼10 nm. Enhancement as well as quenching of luminescence intensity has been observed and it was found that luminescence intensity can be tuned by adding various amounts of silver nanoparticles to the RHO6G dye dispersion. The luminescence spectra of dye consist of two peaks at 440 nm and 550 nm. Peak at 440 nm shows an enhancement in intensity at all the concentrations of added silver nanoparticles with the maximum intensity for dye with 0.25 ml silver nanoparticles (82% enhancement in the luminescence intensity). PL intensity of intense peak at 550 nm of dye molecules was found to be quenched in presence of silver nanoparticles and maximum quenching was found to be 41% for the dye with 1 ml silver nanoparticles. However, for lowest concentration of silver nanoparticles viz. (0.01 ml), enhancement in intensity was observed (13% enhancement than the dye molecules). The quenching as well as enhancement in the intensity can be understood by considering the possibility of three different phenomena. It has been reported earlier that when metal nanoparticles are in close proximity to the fluorophores, quenching of luminescence occurs, whereas when metal nanoparticles are located at certain distance, enhancement in luminescence is observed. This effect has been explained by coupling of surface plasmon resonance from metal nanoparticles with fluorophore, resulting in the increase of excitation and emission rate of the fluorophore in the localized electromagnetic field. The quenching and enhancement of luminescence intensity of the dye molecules can also be explained as the transfer of electrons from dye to the silver nanoparticles and to an extent it can be attributed to the aggregation of dye molecules upon addition of silver nanoparticles.

Synthesis of high molecular weight poly(methyl methacrylate) microspheres by suspension polymerization in the presence of silver nanoparticles

To prepare high molecular weight (HMW) poly(methyl methacrylate) (PMMA)/silver microspheres, methyl methacrylate was suspension-polymerized in the presence of silver nanoparticles using a low-temperature initiator at different conditions. The rate of conversion was increased with increasing initiator concentration. In the case of adding silver nanoparticles, the rate of polymerization decreased slightly. High monomer conversion (about 95%) was obtained in spite of low polymerization temperature of 30 °C. Under controlled conditions, PMMA/silver microspheres with various viscosity-average degree of polymerization (6,000–37,000) were prepared.