Studies on nano suspensions of silver sol and redispersed nanocrystallite silver in aqueous and alcoholic media (original) (raw)
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Ultrasonic Properties of Nanoparticles-liquid Suspensions
A polymer colloidal solution having dispersed nanoparticles of Cu and Au metals have been developed using a novel chemical method. Average size of the nanoparticles could be varied in the 4-10 nm range by conducting the reaction at an elevated temperature of 50-70°C. Colloidal solutions of representative concentrations of 0.1-2.0 wt% Cu/Au contents in the primary solutions are used to study the modified ultrasonic attenuation and ultrasonic velocity in PVA polymer molecules on incorporating the Cu/Au particles. A characteristic behaviour of the ultrasonic velocity and the attenuation are observed at the particular temperature/particle concentration. The results demonstrate that the primary reaction during the nanoparticles-PVA colloidal formation occurs in divided groups in small micelles. The results are analyzed predicting the enhanced thermal conductivity of the samples.
Ultrasonic Dispersion of TiO 2 Nanoparticles in Aqueous Suspension
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The Journal of the Acoustical Society of America, 2014
Liquid droplets of nanometric size encapsulated by a polymer shell are envisioned for targeted drug delivery in therapeutic applications. Unlike standard micrometric gas-filled contrast agents used for medical imaging, these particles present a thick shell and a weakly compressible core. Hence, their dynamical behavior may be out of the range of validity of the models available for the description of encapsulated bubbles. In the present paper, a model for the ultrasound dispersion and absorption in a suspension of nanodroplets is proposed, accounting for both dilatational and translational motions of the particle. The radial motion is modelled by a generalized Rayleigh-Plesset-like equation which takes into account the compressibility of the viscoelastic shell, as well as the one of the core. The effect of the polydispersity of particles in size and shell thickness is introduced in the coupled balance equations which govern the motion of the particles in the surrounding fluid. Both effects of shell compressibility and polydispersity are quantified through the dispersion and absorption curves obtained on a wide ultrasonic frequency range. Finally, some results for larger gas-filled particles are also provided, revealing the limit of the role of the shell compressibility.
Effective ultrasonication process for better colloidal dispersion of nanofluid
Ultrasonics Sonochemistry, 2015
Improving dispersion stability of nanofluids through ultrasonication has been shown to be effective. Determining specific conditions of ultrasonication for a certain nanofluid is necessary. For this purpose, nanofluids of varying nanoparticle concentrations were prepared and studied to find out a suitable and rather mono-dispersed concentration (i.e., 0.5 vol.%, determined through transmission electron microscopy (TEM) analyses). This study aims to report applicable ultrasonication conditions for the dispersion of Al 2 O 3 nanoparticles within H 2 O through the two-step production method. The prepared samples were ultrasonicated via an ultrasonic horn for 1 to 5 h at two different amplitudes (25-and 50%). The microstructure, particle size distribution (PSD), and zeta potentials were analyzed to investigate the dispersion characteristics. Better particle dispersion, smaller aggregate sizes, and higher zeta potentials were observed at 3-and 5 h of ultrasonication duration for the 50-and 25% of sonicator power amplitudes, respectively.
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Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2000
Ultrasonic spectroscopy is a promising measurement technique for the characterisation of emulsions and suspensions over a wide range of particle size and concentration. It appears highly suitable for on-line applications, in particular for dense nano-sized particle systems, where the system stability may be very sensitive to changes in the concentration. In the case of colloidal dispersions the particle sizes are usually smaller than the sound wavelength. Then dissipative processes rather than scattering govern the acoustic behaviour of such systems. The dissipative processes, however, are affected by several material properties, whose significance for the overall acoustic behaviour depends on the type of the material system, e.g. thermal properties are important in the case of emulsions and non-watery suspensions but not for watery suspensions. Often the information on these parameters is incomplete and not sufficiently accurate. In this paper the stability of ultrasonic particle size measurement against incorrect values of the relevant material properties is investigated. This was done firstly by analytical consideration. From this, the degree of influence of the respective material properties on the analysis of spectrometric measurements was derived for oil-water-emulsions, watery and non-watery suspensions. It could be shown that the single properties affect the analysis very differently. In a second step, the conclusions obtained analytically could be confirmed by analysing experimental attenuation spectra with slightly changed material property data. The paper is intended to give users of ultrasonic spectroscopy a practical guide for deciding which material properties have to be obtained with high accuracy and which can be estimated. : S 0 9 2 7 -7 7 5 7 ( 0 0 ) 0 0 5 7 1 -9
Effect of Ultrasonication Duration on Colloidal Structure and Viscosity of Alumina−Water Nanofluid
Industrial & Engineering Chemistry Research, 2014
Nanofluids are promising fluids for heat-transfer applications. Low stability and high viscosity are two important drawbacks for practical applications of nanofluids. The aggregation and sedimentation of nanoparticles are related to the colloidal structure of nanofluids, which directly affects the stability and viscosity. An ultrasonic homogenizer can break the aggregation of particles. The aim of this work was to study the effect of the duration of ultrasonic treatment on colloidal structure, including the stability and temperature-dependent viscosity of a nanofluid. Specifically, a 0.5 vol % Al2O3−water nanofluid was prepared using an ultrasonic homogenizer for various durations from 0 to 180 min. The microstructure, colloid and particle sizes, precipitation, and zeta (ζ) potential were analyzed to investigate the aggregation and sedimentation of the nanofluid. The viscosities of nanofluids subjected to ultrasonic treatment for different durations were also measured at different temperatures from 15 to 45°C. Better particle dispersion, lower particle sizes, smaller colloid sizes, less precipitation, and higher ζ potentials were observed with increasing sonication time. The viscosity of Al2O3−water nanofluid was found to increase with the sonication time up to 60 min and then subsequently decreased. In addition, the viscosity decreased with increasing temperature. The research concluded that more stabler and lower-viscosity nanofluids can be obtained by applying ultrasonic treatment for durations of 90 min or longer.
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Aerosol Science and Technology, 2005
Silver particles less than 20 nm in diameter were synthesized by pyrolysis of an ultrasonically atomized spray of highly dilute aqueous silver nitrate solution at temperatures above 650 • C and below the melting point of silver. Feed solution concentration and ultrasound power applied to the atomizer were found to have a significant impact on the particle size of the silver nanoparticles. Average particle size was found to be controllable in the range of 20 nm to 300 nm by varying the solution concentration and the ultrasound power to the atomizer.
Ultrasonic attenuation by nanoporous particles : Part II: Experimental
Physical Chemistry Chemical Physics, 2006
In Part I of this paper O'Brien presented a new theory that describes the dissipation of ultrasonic energy by porous colloidal particles in suspension. In this paper we present experimental measurements on several such suspensions and compare the resulting ultrasonic attenuation spectra with O'Brien's theory. We find that microporous colloids (e.g. zeolites) and mesoporous colloids (e.g. porous silicas) both show greater attenuation of ultrasound than would solid particles of the same size and effective density, as predicted by O'Brien. Fitting theoretical spectra to the experimental data provides information about the porosity and pore diameters in the particles. This makes the technique potentially suitable as a convenient method of characterizing nanoporous materials, especially those already in suspension.
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Nanofluids (Engineered colloidal suspension of nanoparticles) are the new and promising heat transfer fluids with exceptional properties. Low stability, high pressure drop, and viscosity are the important drawbacks limiting the industrial application of nanofluids. The aggregation and sedimentation of nanoparticles are related to the colloidal structure of nanofluids, which directly affects the stability and viscosity. Various studies revealed that, choosing proper nanoparticle type, size, shape and concentration, base fluid type, operating conditions (pH, temperature, zeta potential, shear, and magnetic field of the solution), ultrasonication probe type, time, power, frequency and intensity, and surfactant type and concentration are the main factors responsible for the nanofluid stability. Among them, ultrasonication treatment is the simplest and most effective technique with longer nanofluid stability period. It is expected that, the present review will provide guidance and contri...