Function Of Nanoparticle Concentration Research Articles

Whole-Pattern Fitting and Positron Annihilation Studies of Magnetic PVA/α-Fe2O3 Nanocomposites

A low-temperature solution combustion method was used to synthesize α-Fe2O3 nanoparticles. Magnetic polyvinyl alcohol (PVA)/α-Fe2O3/NaCl nanocomposites were prepared by solvent cast method. The Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) results are in confirmation with X-ray diffraction (XRD) results indicating the formation of nanocomposites. The microcrystalline parameters, crystallite size (<N>), lattice strain (g in %), stacking faults (α d ), and twin faults (β) of prepared polymer nanocomposites were evaluated by whole-pattern fitting technique. The refinement was carried out using the computed microstructural parameters in which the twin faults and stacking faults did not vary much and statistical deviation was less than 5 %. Positron annihilation lifetime spectroscopy (PALS) was used for microstructural characterization. PALS results show that the ortho-positronium (o-Ps) lifetime (τ3) increases gradually as a function of nanoparticle concentration and about 219 ps increase observed from1.50 to1.71 ns at 3 wt%. This indicates the increase of free volume hole size (V f ) from 54.47 to 72.18 Å3. The o-Ps intensities (I 3) decrease indicating the inhibition of o-Ps formation upon incorporation of nanoparticles into PVA. The increase in I 2 values suggests the increased annihilation at the interface region. Positron lifetime parameters, viz., o-Ps lifetime, and its intensities indicate the effect of quenching and inhibition upon incorporation of metal oxide nanoparticles and inorganic salt into PVA.

Optical absorption measurements of oxide nanoparticles for application as nanofluid in direct absorption solar power systems – Part I: Water-based nanofluids behavior

A promising new generation of solar thermal collector able to enhance the thermal efficiency is the DASC (Direct Absorber Solar Collector). In this paper we report optical absorption measurements performed on several water-based nanofluids (Al2O3, CuO, TiO2, ZnO, CeO2, and Fe2O3) as a function of nanoparticles concentration. These measurements are of fundamental importance to assess the possibility to use the above mentioned metal-oxide nanoparticles in liquid-based nanofluids for direct absorption low temperature flat panel solar collector. The obtained results show different optical behaviors of the nanofluids depending on nanoparticles material and concentration. In all measurements the transmittance rises passing from visible to infrared region and in some cases, when the nanoparticles concentration is too low, the extinction distance grows up to values larger than the typical diameter of a solar receiver.

Dynamic visualization of photothermal heating by gold nanocages using thermoresponsive elastin like polypeptides.

Understanding how plasmonic nanoparticles collectively generate heat upon exposure to light and thus increase the local temperature of the surrounding medium is critical for many applications such as plasmon-assisted microfluidics, plasmonic tweezers, and photothermal cancer therapy. Reliable temperature manipulation requires the capability to spatially and dynamically analyze local temperature profiles as a function of nanoparticle concentration and laser intensity. In this work, we present a novel method for visualization of local temperature increase using elastin-like polypeptides (ELP). We also propose a robust algorithm that allows the construction of reliable calibration curves using known boundary conditions and Boltzmann sigmoid fit applied to the ELP solution's temperature-absorption transfer function. Using this technique, for the first time, we successfully demonstrated how surface and volume distribution of the nano-heaters affect collective heat generation. This approach allows the visualization of dynamic 2D-temperature profiles and simultaneously enables the measurement of specific temperature at any point in a 2D-map. The experimental setup is compatible with conventional optical microscopy and requires no specialized hardware or complex sample preparation. Finally, the real time visualization of plasmonic heating offers an opportunity to control outcomes of thermo-plasmonics which enables a myriad of practical applications.

Copper oxide nano-particles as friction-reduction and anti-wear additives in lubricating oil

Lubricants based on hydrocarbon-type mixtures do not satisfy all requirements of OEMs (Original equipment manufacturers) for modern applications. The usual solution is the addition of small amounts of certain additive compounds that render significant improvements in base oil properties such as oxidative degradation, tribological performance and other characteristics. This study examined the tribological behavior of copper oxide nanoparticles as additives in mineral based multi-grade engine oil. All tests were performed under varying loads and concentrations of nanoparticles in lubricating oil. The friction and wear experiments were performed using pin on disc tribotester. The results demonstrated that nanoparticle additives can effectively improve the engine oil lubricating properties. This is because nanoparticles enter the friction zone along with the flow of lubricant. They convert sliding friction into rolling friction, thus reducing the effective friction coefficient. This work also included an analysis of worn surface morphology by scanning electron microscopy. This surface examination revealed that nanoparticle additives resulted in smoother worn surfaces. From the viscosity test it can be inferred that viscosity of engine oil contains CuO nanoparticles is a function of nanoparticles concentration. Stribeck curves are used to reveal the lubrication regimes where the CuO nano-particles are most effective. It was found that the addition of CuO nanoparticles to the base oil results in up to 50% reduction in coefficient of friction in the mixed lubricant regime.

Thermal conductivity of dry anatase and rutile nano-powders and ethylene and propylene glycol-based TiO2 nanofluids

Thermal conductivity behaviour was studied for two TiO2 nano-powders with different nanocrystalline structures, viz. anatase and rutile, as well as nanofluids formulated as dispersions of these two oxides up to volume concentrations of 8.5% in two different glycols, viz. ethylene and propylene glycol. Because it is known that titanium dioxide can exhibit three different crystalline structures, the dry nano-powders were analysed using X-ray Diffraction to determine the nanocrystalline structure of the powders. Two different techniques were employed in the thermal conductivity study of the materials. Dry nano-powders, with and without compaction, were analysed at room temperature by using a device based on the guarded heat flow meter method. Nanofluids and base fluids were studied with a transient hot wire technique over the temperature range from (283.15 to 343.15)K. The base fluid propylene glycol was measured by using both techniques in order to verify the good agreement between both sets of results. The experimental measurements presented in this work were compared with other literature data for TiO2 nanofluids in order to understand the thermal conductivity enhancement as a function of nanoparticle concentration. Different theoretical or semi-theoretical approaches such as Maxwell, Peñas et al., Yu-Choi were evaluated comparing with our experimental values. A parallel model was used to predict thermal conductivities employing experimental values for dry nanopowder.

Low-threshold and narrow linewidth diffusive random lasing in rhodamine 6G dye-doped polyurethane with dispersed ZrO_2 nanoparticles

We report on low-threshold and narrow linewidth intensity feedback random lasing in rhodamine 6G dye-doped polyurethane with dispersed ZrO2 nanoparticles. Depending on the dye/particle concentration, the lasing threshold is 6.8&#x2013;15.4&#x2009;&#x2009;MW/cm2, and the linewidth is 4&#x2013;6&#xA0;nm. The lasing threshold as a function of nanoparticle concentration is found to follow a power law with an exponent of &#x2212;0.496&#xB1;0.020, which is within uncertainty of Burin et&#xA0;al.&#x2019;s theoretical prediction [Phys. Rev. Lett.87, 215503 (2001)]10.1103/PhysRevLett.87.215503PRLTAO0031-9007.

Tribological analysis of surfactant modified nanolubricants containing CeO2 nanoparticles

Cerium oxide (CeO2) nanoparticles are added to different lubricating oils together with suitable surfactants to obtain modified nanolubricants. Lubricating properties of these surfactant modified nanolubricants have been investigated using a pin on disc tribotester under boundary lubrication conditions. Coconut oil, paraffin oil and a commercial engine oil (SAE15W40) have been used as base oils for the present study. Changes in frictional coefficient and specific wear rate have been studied as a function of nanoparticle concentration in the lubricant together with an estimation of the settling trend of nanoparticles with time. Results show that the frictional force and specific wear rate decrease with increase in concentration of nanoparticles, come to a minimum at a specific concentration level and then increase, showing the presence of an optimum concentration level at which both friction and wear are the least. At this concentration level, coconut oil shows the lowest frictional coefficient and specific wear rate among the three oils studied. The morphology of the pin surfaces after sliding has been studied using atomic force microscopy, optical interferometer and SEM. When CeO2 nanoparticles are added to the lubrication oil together with surfactant modification, settling trend and agglomeration of nanoparticles with time are reduced to a great extent compared to the case in which nanoparticles are added without surfactant modification.

The improvement of characteristics of biodegradable films made from kefiran–whey protein by nanoparticle incorporation

Biodegradable kefiran–whey protein isolate (WPI) nanocomposites were produced using montmorillonite (MMT) and nano-TiO2 as nanoparticles in the percentage of 1, 3, and 5% (w/w) by a casting and solvent-evaporation method. Physical, mechanical, and water-vapor permeability (WVP) properties were determined as a function of nanoparticle concentration. The results revealed that the effect of these nanoparticles was different according to their nature and percentage. The films incorporated with 5% (w/w) MMT showed the highest tensile strength, Young's modulus, puncture strength, and the lowest WVP compared with the control and TiO2 added films. In contrast to MMT, addition of TiO2 nanoparticles due to the plasticizing effect led to a significant change in color and transparency of nanocomposite. Scanning electron microscopy (SEM) observations demonstrated the films’ properties in relation to their microstructures. The surface topography results also showed a considerable increase in roughness parameters by incorporating the nanoparticles in kefiran–WPI matrix.

Investigation on Likely Effects of Ag, TiO2, and ZnO Nanoparticles on Sewage Treatment

Because of the increasing number of applications of nanoparticles (NPs), particularly in food, personal care products, etc., these materials pose a potential threat to the environment. The performance of municipal wastewater treatment plants could be adversely affected if NPs ultimately reach these plants. In this study, the effects of silver, titania and zirconia NPs on the micro-organisms responsible for decomposition of organic matter was assessed and related to the performance of sewage treatment plants. Statistical analysis using the most probable number test demonstrated a relationship between NP concentration and parameters related to bacterial decomposition of wastewater. A sequencing batch reactor experiment demonstrated deteriorating performance of the reactor in terms of reduced chemical oxygen demand and biological oxygen demand as a function of NP concentration. The presence of NPs in influent (untreated) wastewater was found to necessitate increased hydraulic residence times to maintain the desired performance of the plant.

Turbulent mass transfer of Al2O3 and TiO2 electrolyte nanofluids in circular tube

Experimental study was performed to investigate turbulent mass transfer in straight circular tube. Electrochemical limiting diffusion current technique was used to measure the mass transfer coefficient in fully developed hydrodynamics and under developed mass transfer region. TiO2 and γ-Al2O3 nanoparticles were added into the electrolyte solution (ES) to make electrolyte nanofluids (ENF). Measurements revealed that enhancement in mass transfer reaches 10 % in a 0.01 vol% γ-Al2O3/electrolyte nanofluid while 18 % in a 0.015 vol% TiO2/electrolyte nanofluid relative to the base ES. Mass transfer coefficients increased with nanoparticles concentration up to an optimum concentration (0.01 % in γ-Al2O3/electrolyte nanofluid and 0.015 % in TiO2/electrolyte nanofluid) while decreased by increasing nanoparticles concentration further. Enhancement ratio which is the ratio of the mass transfer coefficient of nanofluid to that of the base fluid was a function of nanoparticle concentration and was independent of Reynolds number. The mechanisms of nanoparticles Brownian motion and nanoparticles clustering were used to describe the behavior of the enhancement ratio in ENF.

Enhanced thermophysical properties of copper nanoparticles dispersed in gear oil

Stable and well dispersed Cu-gear oil (IBP Haulic-68) nanofluids having Cu nanoparticles volume concentration between 0.11 and 2% are prepared with oleic acid surfactant. Presence of agglomerated Cu nanoparticles in the prepared nanofluids is confirmed from Dynamic Light Scattering (DLS) data. Thermal conductivity and viscosity measurements are performed both as function of nanoparticle concentration and temperature between 10 and 80 °C. Thermal conductivity enhancement of 24% is observed with 2 vol% of Cu nanoparticle loading at room temperature. The formation of interfacial layer at the nanoparticle–liquid boundary and the ballistic transport of phonons across the percolating aggregates are believed to be responsible for the observed thermal conductivity enhancement. Viscosity of Cu (2 vol%)–gear oil nanofluids shows ∼71% enhancement at 30 °C. Newtonian behavior of gear oil changes to non-Newtonian behavior with the appearance of shear thinning for higher loading of Cu nanoparticles. Modified Krieger–Dougherty equation considering the role of aggregation predicts reasonably well Cu vol% dependence of viscosity of Cu-gear oil nanofluids and its temperature dependence is well accounted by the modified Andrade equation.

Liquid-layering induced, temperature-dependent thermal conductivity enhancement in ZnO–propylene glycol nanofluids

Experiments were carried out on preparation of colloidal dispersions of ZnO nanoparticles in propylene glycol leading to ZnO–propylene glycol nanofluids. Thermal conductivity of these nanofluids was measured as a function of nanoparticle concentration (⩽2vol.%), temperature (10–60°C) and aggregate size. A strong dependence of thermal conductivity enhancement on temperature with higher enhancements at lower temperatures has been observed. Our results on temperature and aggregation dependence of thermal conductivity enhancement show that the thermal conductivity enhancement in ZnO–propylene glycol nanofluids is attributed to formation of solvation layers (liquid layers) of base fluid on the ZnO nanoparticle surfaces.

Modeling hierarchically structured nanoparticle/diblock copolymer systems

Despite progress in theories and simulations, the structure prediction of self-assembled materials beyond simple model systems remains a grand challenge. In this work, we present a molecular modeling approach for predicting the nanostructure of hybrid systems based on AB diblock copolymers and nanoparticles decorated with A, B, or mixed A/B homopolymer ligands. Using mesoscopic simulations, we derived phase diagrams as a function of nanoparticle concentration and decoration.

Degradation of polypropylene carbonate through plasmonic heating

We report the thermal degradation of a solid film of polypropylene carbonate, driven by the photothermal effect of gold nanoparticles. We provide characterization of the products of this chemical reaction and use the known activation barrier for this chemical reaction to discuss the temperatures obtained in the film. In addition, we report the efficiency of the reaction as a function of nanoparticle concentration and find nanoparticles to be significantly more effective than an organic dye at driving this reaction.

Slightly hydrophobic silica nanoparticles for enhanced oil recovery: interfacial and rheological behaviour

This paper is aimed at studying AEROSIL® R816 nanoparticle behaviour to see if it has enough feasibility to be used as a chemical agent in enhanced oil recovery (EOR) processes. The main focus is on interfacial and rheological behaviour of this particle in aqueous and polymeric media. Interfacial tension measurements between aqueous nanoparticle suspensions and oil showed that AEROSIL® R816 particles were able to reduce the interfacial tension between water and oil to half of its original value. This property led to development of stabilised oil in water emulsions. Moreover, viscosity measurements showed that AEROSIL® R816 had a great ability in rheology modification of aqueous solutions. The solution viscosity was studied as a function of nanoparticle concentration and shear rate. It was seen that viscosity rose as the nanoparticle concentration was increased. From the standpoint of shear dependency, two regions of shear thinning behaviour were observed for different shear rate regions. Finally, by dissolving a fixed amount of a low molecular weight polyacrylamide into nanoparticle suspensions of different concentrations, the stability of R816 suspensions was significantly improved. This addition also resulted in almost considerable enhancement of nanoparticle thickening property. (Received: January 15, 2012; Accepted: July 17, 2012)

Structural and Dielectric Properties of CdS Nanoparticle Embedded Polyurethane Nanocomposite Samples

AbstractThe polymer nanocomposite samples have been prepared by solution embedding of CdS nanoparticles in polyurethane (PU). The structural properties have been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM and AFM images represent the dispersion of CdS nanoparticles in a polymer matrix. The permittivity of nanocomposite samples increases with temperature due to formation of new dipoles or accumulation of charge carriers in a nanoparticle‐‐polymer interface. The increase in permittivity with temperature can be attributed to the heat‐assisted dipole moment. Furthermore, it has been observed that permittivity is the function of nanoparticle concentration, temperature, and frequency. The high concentration of nanoparticles lowers permittivity with frequency. The positive and negative tangential loss has been observed in PU‐‐CdS nanocomposite samples. The negative loss phenomenon could be understood in terms of a local space charge separation. The phase transition of PU and PU‐‐CdS nanocomposites has been studied by using a thermally stimulated discharge current technique. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E274–E286, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21273

Measurement and Model Validation of Nanofluid Specific Heat Capacity with Differential Scanning Calorimetry

Nanofluids are being considered for heat transfer applications; therefore it is important to know their thermophysical properties accurately. In this paper we focused on nanofluid specific heat capacity. Currently, there exist two models to predict a nanofluid specific heat capacity as a function of nanoparticle concentration and material. Model I is a straight volume-weighted average; Model II is based on the assumption of thermal equilibrium between the particles and the surrounding fluid. These two models give significantly different predictions for a given system. Using differential scanning calorimetry (DSC), a robust experimental methodology for measuring the heat capacity of fluids, the specific heat capacities of water-based silica, alumina, and copper oxide nanofluids were measured. Nanoparticle concentrations were varied between 5 wt% and 50 wt%. Test results were found to be in excellent agreement with Model II, while the predictions of Model I deviated very significantly from the data. Therefore, Model II is recommended for nanofluids.

Electrohydrodynamic instabilities of polymer thin films: Filler effect

The influence of various nanoparticles with different dimension, density, dielectric constant, and surface property on electrohydrodynamic (EHD) instabilities of polymer/nanoparticle nanocomposite thin films was examined as a function of nanoparticle concentration. Transmission electron microscopy (TEM) images of polystyrene (PS)/nanoparticles (NPs) thin films demonstrated that all the nanoparticles were uniformly distributed in polymer matrix and the homogeneous dispersions of nanoparticles were not affected by thermal annealing above glass transition temperature. Optical microscopy (OM) observations indicated that thin films of polystyrene containing silica (SiO 2), gold (Au), cadmium selenide (CdSe), and titania (TiO 2) nanoparticles showed electrohydrodynamic instability patterns similar to those seen in pure polystyrene, up to 3 vol% nanoparticles. The presence of nanoparticles changed the dielectric constant of the thin films, which led to systematic variations in the wavelengths of the surface instabilities, which were consistent with calculated values. Cross-sectional transmission electron microscopy (TEM) images showed that migration or aggregation of the nanoparticles occurred only for silica contrary to other nanoparticles. This work points to a simple route to reduce the scale of final well-ordered columnar structures.

Nanostructured diblock copolymer films with embedded magnetic nanoparticles

Nanostructured diblock copolymer films with embedded magneticnanoparticles are prepared by solution casting. The diblock copolymerpolystyrene-block-polymethylmethacrylate with a fully deuterated polystyrene block of aweight ratio of 0.22 is used as a structure-directing matrix. Maghemite nanoparticles (γ-Fe2O3) are coated with polystyrene and thus have a selective affinity to the minority block of thediblock copolymer. The hybrid film morphology is investigated as a function ofnanoparticle concentration. The surface structure is probed with atomic force microscopyand scanning electron microscopy. The inner film structure and the structure atthe polymer–substrate interface are detected with grazing incidence small angleneutron scattering (GISANS). Irrespective of the nanoparticle concentration a welldeveloped micro-phase separation structure is present. From the Bragg peaksobserved in the GISANS data a linear nanoparticle concentration dependence of theinter-domain spacing of the micro-phase separation structure is determined. Thesuperparamagnetic and blocking behavior can be explained with a generalizedStoner–Wohlfarth–Néel theory which includes either an elastic torque being exerted onthe nanoparticles by the field or a broad distribution of anisotropy constants.

Quantitative 1H MRI, 19F MRI, and 19F MRS of cell‐internalized perfluorocarbon paramagnetic nanoparticles

In vivo molecular imaging with targeted MRI contrast agents will require sensitive methods to quantify local concentrations of contrast agent, enabling not only imaging-based recognition of pathological biomarkers but also detection of changes in expression levels as a consequence of disease development, therapeutic interventions or recurrence of disease. In recent years, targeted paramagnetic perfluorocarbon emulsions have been frequently applied in this context, permitting high-resolution (1)H MRI combined with quantitative (19)F MR imaging or spectroscopy, under the assumption that the fluorine signal is not altered by the local tissue and cellular environment. In this in vitro study we have investigated the (19)F MR-based quantification potential of a paramagnetic perfluorocarbon emulsion conjugated with RGD-peptide to target the cell-internalizing α(ν)β(3)-integrin expressed on endothelial cells, using a combination of (1)H MRI, (19)F MRI and (19)F MRS. The cells took up the targeted emulsion to a greater extent than nontargeted emulsion. The targeted emulsion was internalized into large 1-7 µm diameter vesicles in the perinuclear region, whereas nontargeted emulsion ended up in 1-4 µm diameter vesicles, which were more evenly distributed in the cytoplasm. Association of the targeted emulsion with the cells resulted in different proton longitudinal relaxivity values, r(1), for targeted and control nanoparticles, prohibiting unambiguous quantification of local contrast agent concentration. Upon cellular association, the fluorine R(1) was constant with concentration, while the fluorine R(2) increased nonlinearly with concentration. Even though the fluorine relaxation rate was not constant, the (19)F MRI and (19)F MRS signals for both targeted nanoparticles and controls were linear and quantifiable as function of nanoparticle concentration.