Concentration Of Nanoparticles In Suspension Research Articles

Limitations of Nanoparticles Size Characterization by Asymmetric Flow Field\u2011Fractionation Coupled with Online Dynamic Light Scattering

The development of reliable protocols suitable for the characterisation of the physical properties of nanoparticles in suspension is becoming crucial to assess the potential biological as well as toxicological impact of nanoparticles. Amongst sizing techniques, asymmetric flow field flow fractionation (AF4) coupled to online size detectors represents one of the most robust and flexible options to quantify the particle size distribution in suspension. However, size measurement uncertainties have been reported for on-line dynamic light scattering (DLS) detectors when coupled to AF4 systems. In this work we investigated the influence of the initial concentration of nanoparticles in suspension on the sizing capability of the asymmetric flow field-flow fractionation technique coupled with an on-line dynamic light scattering detector and a UV–Visible spectrophotometer (UV) detector. Experiments were performed with suspensions of gold nanoparticles with a nominal diameter of 40 nm and 60 nm at a range of particle concentrations. The results obtained demonstrate that at low concentration of nanoparticles, the AF4-DLS combined technique fails to evaluate the real size of nanoparticles in suspension, detecting an apparent and progressive size increase as a function of the elution time and of the concentration of nanoparticles in suspension.

Electrophoretic deposition of ZnO-CeO2mixed oxide nanoparticles

ZnO–CeO2 nanoparticles were synthesized by microwave combustion and deposited by electrophoretic deposition (EPD). The effect of using two different alcohols, ethanol and methanol, was investigated on EPD behavior and morphology of deposited film. Moreover, the effect of concentration of nanoparticles and applied voltage on the mass of deposit and the variation in the current density were investigated. With a change in the alcohol type, the surface morphology of deposition changed and some voids were observed on the deposition surface in ethanol. In all cases, with increasing concentration of nanoparticles in suspension, the number of developed cracks increased. Besides, a rise in voltage led to an increase in the number of cracks. The EPD processes in ethanol and methanol suspension were simulated over time using different zero boundary conditions. Hemi-spherical morphology was seen for the nanoparticles deposited in ethanol. This kind of growth was simulated based on the changes in electrical field.

Experimental studies on viscosity, thermal and electrical conductivity of aluminum nitride–ethylene glycol (AlN–EG) nanofluids

The paper presents the results of experimental research studies carried out on basic physical properties of aluminum nitride–ethylene glycol nanofluids. Nanofluids were prepared with two step method with use of the commercial available AlN nanoparticles. Dynamic viscosity of the material in the range of shear rates from 0.01 to 1000s−1 at pressure 0.1MPa, and constant temperature of 298.15K was measured. Thermal conductivity was measured using the transient line heat source method at a constant temperature of 298.15K. Finally the electrical conductivity at constant temperature of 298.15K was measured. It was presented that this material exhibits non-Newtonian nature and thermal conductivity increases linearly with the concentration of nanoparticles in suspension. AlN–EG nanofluid presents also a significant increase in electrical conductivity with the concentration of nanoparticles.

Detection of Carbon Nanoparticles in Suspension by a Photothermal Technique

In this article, a photothermal technique is presented to detect carbon nanoparticles in suspension and to determine their concentration using the photothermal lens effect and the photothermal beam deflection. Both methods are well researched and described in the corresponding literature. The experimental setup consists of an excitation and a probe laser, and optical devices for beam guidance and signal detection. First, an optical setup to generate both effects in a suspension simultaneously is described. To detect the beam deflection and the beam expansion of the probe beam, different optical detectors were applied; moreover, a graphical CMOS-camera-based method was developed. The dependence of the photothermal effect on the absorption of the pump laser beam is discussed, particularly by varying the concentration of carbon nanoparticles in suspension. It is shown that the absorption of the pump beam and thus the photothermal effects can be modified by changing the concentration of carbon nanoparticles. The measurements with this system are showing that, especially with the graphical method, a determination of the concentration in the low ng\(\cdot \)ml\(^{-1}\) range is possible.

Effect of TiO2 nanoparticles dispersion on ionic behaviour in nematic liquid crystal

The present study focuses on the ionic behaviour in nanoparticles (NPs) dispersed nematic liquid crystal. Dielectric spectroscopy has been used to investigate the behaviour of ions in suspension of NPs and liquid crystal (LC). Ionic concentration, diffusion coefficient, activation energy and mobility have been calculated from dielectric data. It is found that ion concentration increases initially and then it decreases with increasing concentration of NPs in suspension. The initial increase in ion concentration is attributed to the insertion of more ions due to impurities of TiO2 NPs and various other reasons. Temperature dependence of diffusion constant for different loading of TiO2 NPs is also investigated. The activation energy of NPs dispersed LC is found to be lower than the pristine one and it decreases with increasing concentration of NPs. The decreasing DC conductivity with increasing NPs concentration is attributed to the hindered or restricted motion of ions in the suspension. It is proposed that TiO2 NPs may be a potential candidate to be used to suppress the undesired ionic effect in LCs.

Alpha chymotrypsin coated clusters of Fe3O4nanoparticles for biocatalysis in low water media

BackgroundEnzymes in low water containing non aqueous media are useful for organic synthesis. For example, hydrolases in such media can be used for synthetic purposes. Initial work in this area was carried out with lyophilized powders of enzymes. These were found to have poor activity. Drying (removing bulk water) by precipitation turned out to be a better approach. As enzymes in such media are heterogeneous catalysts, spreading these precipitates over a large surface gave even better results. In this context, nanoparticles with their better surface to volume ratio provide obvious advantage. Magnetic nanoparticles have an added advantage of easy separation after the reaction. Keeping this in view, alpha chymotrypsin solution in water was precipitated over a stirred population of Fe3O4 nanoparticles in n-propanol. This led to alpha chymotrypsin activity coated over clusters of Fe3O4 nanoparticles. These preparations were found to have quite high transesterification activity in low water containing n-octane.ResultsPrecipitation of alpha chymotrypsin over a stirred suspension of Fe3O4 nanoparticles (3.6 nm diameter) led to the formation of enzyme coated clusters of nanoparticles (ECCNs). These clusters were also magnetic and their hydrodynamic diameter ranged from 1.2- 2.6 microns (as measured by dynamic light scattering). Transmission electron microscopy (TEM), showed that these clusters had highly irregular shapes. Transesterification assay of various clusters in anhydrous n-octane led to optimization of concentration of nanoparticles in suspension during precipitation. Optimized design of enzyme coated magnetic clusters of nanoparticles (ECCN 3) showed the highest initial rate of 465 nmol min-1 mg-1protein which was about 9 times higher as compared to the simple precipitates with an initial rate of 52 nmol min-1 mg-1 protein.Circular Dichroism (CD)(with a spinning cell accessory) showed that secondary structure content of the alpha Chymotrypsin in ECCN 3 [15% α-helix, 37% β-sheet and 48% random coil] was identical to the simple precipitates of alpha chymotrypsin.ConclusionA strategy for obtaining a high activity preparation of alpha chymotrypsin for application in low water media is described. Such high activity biocatalysts are useful in organic synthesis.

Dispersion stability of nanoparticles in ecotoxicological investigations: the need for adequate measurement tools

One of the main challenges in nanoecotoxicological investigations is in the selection of the most suitable measurement methods and protocols for nanoparticle characterisation. Several parameters have been identified as being important as they govern nanotoxicological activity, with some parameters being better defined than others. For example, as a parameter, there is some ambiguity as to how to measure dispersion stability in the context of ecotoxicological investigations; indeed, there is disagreement over which are the best methods to measure nanoparticle dispersion stability. The purpose of this article is to use various commercially available tools to measure dispersion stability and to understand the information given by each tool. In this study, CeO2 was dispersed in two different types of media: de-ionised water and electrolyte-containing fish medium. The DLS mean particle size of freshly dispersed sample in DI water was ~200 nm in diameter. A visual sedimentation experiment showed that nanoparticle dispersion made in the fish medium was less stable compared to corresponding dispersion in de-ionised water. Stability of these dispersions was monitored using various techniques, for a period of 3 days. Our findings have shown that dispersion stability can be suitably assessed by monitoring: (a) surface charge, (b) sedimentation events and (c) presence of agglomerates, through time. The majority of techniques employed here (zeta potential, particle size via DLS, fluorescence and UV–Vis spectroscopy and SEM) were shown to provide useful, complementary information on dispersion stability. Nanoparticle Tracking Analysis (NTA) provides useful, quantitative information on the concentration of nanoparticles in suspension, but is limited by its inability to accurately track the motion of large agglomerates found in the fish medium.