Testing Micro- and Nanoparticles in a Dynamic Environment

Suspending of solid particles in liquid by agitators

This paper is a review of studies on the motion of solid particles in perfect and viscous liquids under the action of time-average forces caused by an acoustic field. Emphasis is on studies that employed a method based on solving the hydromechanic equations for a compressible liquid and evaluating and averaging the forces acting on particles

The rheology of suspensions of solid particles in aqueous matrix liquids thickened by starch nanoparticles (SNP) was investigated. The SNP concentration varied from 9.89 to 34.60 wt% based on the aqueous matrix phase. The solids concentration of suspensions varied from 0 to 47 wt% (0 to 56 vol%). The suspensions at any given SNP concentration were generally Newtonian at low solids concentrations. At high solids concentrations, the suspensions were non-Newtonian shear-thinning. With the increase in the SNP concentration, the suspensions become non-Newtonian at a lower solids concentration. The rheological behavior of non-Newtonian suspensions could be described adequately with a power-law model. The consistency index of the suspension increased with the increase in solids concentration of the suspension at any given SNP concentration. The flow behavior index of suspensions was well below unity at high solids concentrations, indicating non-Newtonian shear-thinning behavior. The value of the flow behavior index decreased with the increase in solids concentration indicating an enhancement of shear-thinning in suspensions. The experimental viscosity and consistency data for Newtonian and non-Newtonian suspensions showed good agreement with the predictions of the Pal viscosity model for suspensions.

Many current problems of ecological mechanics must be solved with incomplete information about the motion of large aggregates of liquid and solid particles in liquid and gas flows [1–5]. These problems require the averaging of physical fields [6], calculation of the moments of random variables [7], and experimental determination of the bulk characteristics of particles [1, 2, 5, 8] and their use in mechanical calculations. One of these characteristics is the bulk harmonic (or mean harmonic) fall velocity of particles. As will be shown below, this quantity can be directly determined from the curve of sediment-mass accumulation for small concentrations of particles in a stationary liquid. The comparison of two expressions for the bulk time of the sedimentation of particles indicates that

In this study, the analogy between transient heat conduction and mass transfer is applied to investigate the dissolution behavior of solid particles in liquids, particularly, for the transport phenomenon associated with the controlled drug release process. Mathematical modeling is established assuming the shrinking core is solely caused by the diffusion mechanism. The transport governing equations for the dissolution process of controlled drug release are compared with the transient heat conduction differential equations. Analogous quantities, certain analytical solutions and numerical solutions for complex geometry are obtained to demonstrate the dissolution behavior of this specific type of solid particles in liquids based on the proposed shrinking core model. It is found that the shape of the drug capsule plays an important role for effective and timely release of drug content after intake. Among the three shapes investigated herein, sphere, cube and cuboid, we conclude that the drug concentration in a cuboid shaped drug head depletes the quickest whereas the spherical shaped head dissolves the slowest.

Optical resonators have enabled the label-free measurement of nanoparticles suspended in liquids, down to the resolution of individual viruses and large molecules, but are only able to quantify optical properties (refractive index, scattering, fluorescence). Additionally, these sensors are fundamentally limited by the random diffusion of particles to the sensing region, and thus only measure a tiny fraction of the analyte. We have developed a microfluidic optomechanical resonator capable of sensing freely flowing nanoparticles using the action of phonons that are coupled to light. The phonon mode of the system casts a nearly perfect net for measuring density, viscoelasticity, and compressibility of the particles that flow through, without being limited by random diffusion. Information on the mechanical properties of the particles is encoded in the light scattered from the thermal fluctuations of the phonon mode. We have also developed a new electro-opto-mechanical method for improving the sensing speed achievable with this technique. We demonstrate real-time particle transit measurements as fast as 400 microseconds, without any post-processing. We discuss how this novel technique can be used for ultra-high throughput analysis of mechanical properties of biological particles in liquids, enabling a new form of flow cytometry. (invited by Prof. Giuseppe Leo)

The aim of the study is to find the role of lead zirconate titanate (PZT) in the phase formation of poly vinylidene fluoride (PVDF) and its effect on electrical and structural properties of PZT-PVDF composites (50 Vol%) with 0–3 connectivity. PZT particles of different sizes ranging from micron to nano are used. The particle size (<100 nm) were determined from TEM and the broadening of the characteristic diffraction peaks in the x-ray diffraction (XRD) pattern. Scanning electron microscopy (SEM), studies were performed to analyze the nature of ceramic particle distribution within the matrix. The percentage of polymer crystallinity was determined from differential scanning calorimetry (DSC) and found to decrease with decrease in ceramic particle size. The decrease in the crystallinity percentage is due the hindrance offered by ceramic during the crystallization of the polymer. The melting endotherms of the composites were deconvoluted and the amount of PVDF β-phase present in the composites were determined and was found to decrease with decrease in ceramic particle size. Fourier transform infrared spectroscopy (FTIR) studies were also carried out to confirm the decrease in the β-phase content with decrease in particle size. The variation in the amount of β-phase of the polymer is due to the presence of PZT which acts as a source of electric field during poling and converts other polymer phases to β-phase. The piezoelectric coefficient and remnant polarization was found to decrease with decrease in ceramic particle size and is due to the decrease in percentage of β phase in the composites.

Transport of solid particles in microfluidic channels

Ultrasonic measurement and characterization of a low concentration system of solid particles in liquid, in high shear flow

Dissolution of solid particles in liquids

Dissolution of solid particles in liquids: A reaction—diffusion model

A study has been made of anomalous diffraction effects in the sizing of solid particles in liquids using a Malvern laser diffraction sizer. The particles were N.B.S. standard reference material 1004 glass spheres. The five liquids used were chosen to give a range of refractive index (R.I.) above and below that of the glass; the ratio of solid R.I. to liquid R.I. (m) ranged from 0.92 to 1.15. Measurements were made of the change in the light energy distribution pattern as the value of | m − 1 | was in creased or reduced towards zero. At high values of | m − 1 | the measured light energy distribution pattern was predicted adequately by the Fraunhofer diffraction approximation to Mie theory and the Fraunhofer computer software could be used to derive particle size distribution from the light energy pattern. For values of | m − 1 | near to zero, the Fraunhofer approach was in error but the anomalous diffraction approximation and software proved adequate for the back‐calculation of size distribution from energy pattern.

The dissolution of solid particles in liquids has been analysed theoretically. Here, the heat of dissolution is taken into account. The unsteady state moving-boundary problem is solved through a perturbation approach. The perturbation parameter ε, defined as the ratio [(solubility – bulk solute concentration)/density of solid], can be used to determine whether the pseudo-steady state assumption often made in the conventional analysis is appropriate. The results of numerical calculations reveal that for the dissolution of non-dissociating substances in water if the variations in both the temperature and the concentration in the bulk liquid phase are negligible, the effect of heat on the kinetic behaviour under consideration is insignificant. Depending on the magnitude of ε, a pseudo-steady state assumption may lead to appreciable deviation.

Transport and deposition of solid particles in a differentially heated cavity at high Rayleigh numbers up to 108 was studied using an Eulerian–Lagrangian computational method. Two-dimensional Navier-Stokes and energy equations were solved and the motions of particles with diameters in the range of 10 nm to 10 μm were simulated. Effects of drag, lift, thermophoresis and Brownian forces on the particle trajectories were investigated. It was observed that the variation of Rayleigh number can significantly change the flow field and the corresponding particle deposition patterns. In particular, recirculation regions were formed near the corners as the Rayleigh number increased. Furthermore, the effects of changes in the Rayleigh numbers on transport and deposition of particles of different sizes were quite different. Increasing Rayleigh number from 107 to 108 caused a decrease in particles deposition except for 10 μm particles. Smaller particles had a higher probability to deposit on the cold wall as the thermophoresis effect becomes important. Increasing the Rayleigh number decreased the influencing zone of the thermophoresis in the vicinity of the walls. Copyright 2012 American Association for Aerosol Research

It is important to predict the pressure loss due to hydraulic transport of large solid particles for the design of subsea mining system. The mixture flow in the lifting pipe is expected to be unsteady in the actual mining system. The authors develop the one-dimensional mathematical model to predict the pressure loss of pulsating mixture flow in a static vertical pipe assuming that the flow in the pipe is fully developed. The experiment on hydraulic transport of solid particles was carried out to obtain the data for the investigation of the effects of flow fluctuation on pressure loss in a static vertical pipe. In the experiment, alumina beads and glass beads were used as solid particles, and the experimental parameters were mixture velocity, solid concentration, pulsating period, and pulsating amplitude. The proposed model was validated by a comparison with experimental data. Furthermore, we calculated the pressure losses due to hydraulic transports of polymetallic sulfide ores and manganese nodules using the proposed model. The calculation results showed that the fluctuating component in pulsating mixture flow should be considered for the design of lifting system and that the homogeneous mixture model could not be applied to the prediction of the pressure loss unless the mixture concentration is low and the pulsating period is short.