Modeling the release of nanoparticles from mobile microcapsules

The authors present a novel computational approach to simulate both the release of nanoparticles from a microcapsule, which is moving through a microchannel, and the adsorption of the released particles onto the channel walls. By integrating the lattice spring model for the micromechanics of elastic solids and the lattice Boltzmann model for fluid dynamics, they simulate the relevant fluid-structure interactions in the system. In particular, they capture the dynamic interactions among the capsule's elastic shell, the encapsulated fluid, and the external, host solution. The nanoparticles are treated as "tracer particles" and their motion is modeled via a Brownian dynamics simulation. An imposed pressure gradient drives the capsule to move along an adhesive substrate and the particles are released from the surface of this mobile capsule. The authors determine how the elasticity of the capsule, the strength of the capsule-surface adhesion and the diffusion coefficient of the nanoparticles affect the relative amount of particles that are adsorbed onto the substrate. In addition to showing that the compliant nature of the capsule can significantly affect the nanoparticle deposition, they isolate a range of parameters for maximizing the adsorbed amount. The findings yield guidelines for optimizing the efficiency of microcapsule carriers in the targeted delivery of nanoparticles.     

Particle deposition onto Janus and patchy spherical collectors

An Eulerian model (convection-diffusion-migration equation) is presented to study colloid deposition behavior on Janus and patchy spherical collectors using Happel cell geometry. The model aims to capture the effect of the collector surface charge heterogeneity on the particle deposition rate. Two separate cases of surface charge distribution are presented. In the first case, the surface heterogeneity is modeled as half the collector favoring deposition and the other half hindering it (Janus collectors). For the second case, the surface heterogeneity is modeled as alternate stripes of attractive and repulsive regions on the collector (patchy collectors). The model also considers fluid flow approaching the collector at different angles in addition to the standard gravity assisted and gravity hindered flow conditions to analyze the effect of the collector orientation on the deposition. It was observed that particles tend to deposit at the edges of the favorable stripes and the extent of this preferential accumulation varies along the tangential position of the collector due to the nonuniform nature of the collector. The predicted deposition behavior is compared to the patchwise heterogeneity model. The study brings to fore how recent developments in synthesis of chemically heterogeneous particles and beads can be used for improved particle capture in porous media and for designing filter beds with enhanced life.     

Deposition of particles under external forces in laminar flow through parallel-plate and cylindrical channels

A theoretical analysis of particle deposition kinetics onto walls of parallel-plate and cylindrical channels is presented. Rigorous transport equations are formulated by taking into account specific surface forces as well as external forces, e.g., gravity. By solving the transport equations numerically, the dimensionless mass transfer Sherwood number is determined as a function of various dimensionless parameters introduced such as Pe, Gr, Ad, and Dl, accounting for convection and diffusion, and for gravity, dispersion, and electrical double-layer interactions, respectively. The influence of attractive surface forces and gravity on the deposition kinetics is graphically presented and discussed. For large particles, i.e., about 1-μm diameter (Pe > 1), and for short distances from the point where deposition starts, a considerable increase in particle flux (up to an order of magnitude) is predicted over previous analytical values when strong attractive double-layer forces are present. For particles smaller than 0.1-μm diameter (Pe < 10^-4) our numerical results show that particle deposition rates may be successfully predicted by an analytical formula derived for particles of negligible size even in the presence of double-layer attractions (provided external forces are absent). Experimental results reported in the literature obtained under conditions of negligible gravity force are reinterpreted in terms of the present theory. A somewhat closer agreement with experimental data as compared to the analytical formula mentioned above is found in cases of strong double-layer attractions.     

Hydrodynamic boundary layer at a rising air bubble and entrapment of fine solids: Gravity effects on particle–bubble interactions

A model study of the dynamic interactions of fine non-neutrally buoyant solids with background boundary layer (BL) flow on rising bubbles is developed. The aim is to clarify the specific role of the gravity effects. The approach is based on the acquisition of asymptotic equations about the disturbed flow field in the particle vicinity and accounts for both viscous deformation and sedimentation effects. It is established that two particle density regions are of major interest. In Region I the coupling of hydrodynamic and gravity effects results in granulometric separation of the solids. In Region II the role of particle sedimentation dominates over the purely hydrodynamic interactions. As a result, the lighter the particles are, and the smaller their sizes are, the more important is the granulometric effect inside the BL. For high-density fines and larger bubbles, the gravity effects couple with the BL flow. The particle capture results in significant amplification of the collision chances. The obtained results are expected to refine the approach to recovery of fine species from ground materials in conventional flotation and should be taken into account in the assessment of the overall capture efficiency for fine particles in microflotation and separation processes.     

Characterization of latex particle arrays by gas adsorption

Assemblies of colloidal particles are frequently used in novel applications, and this requires nondestructive methods allowing overall characterization of the sample and collection of information about the quality of the arrays. From suspensions of polystyrene, poly[styrene-co-(2-hydroxyethylmethacrylate)], poly[styrene-co-acrylic acid], and poly[styrene-co-methacrylic acid], assemblies of spherical particles were obtained by elimination of the solvent in different ways-evaporation, gravity deposition, and filtration. These latex particle packings were characterized by scanning and transmission electron microscopy and by gas adsorption to determine the efficiency of packing. The surface area, total pore volume, and pore size distributions obtained from the adsorption and desorption data were related to characteristic parameters calculated for cubic close-packed spherical particles.     

Effect of Pt particle size and distribution on photoelectrochemical hydrogen evolution by p-Si photocathodes

In this work, we investigate the effect of the average size and density of Pt clusters on silicon on the photoelectrochemical production of hydrogen. The metallization of Si is performed via electroless deposition from aqueous HF solutions and from water-in-oil microemulsions. The first method enables control of the average diameter and density of Pt clusters by properly changing the deposition parameters like HF concentration and immersion times. However, on one hand, size dispersion is relatively wide and particles agglomeration may occur with this deposition technique. On the other hand, Pt islands with smaller dimensions at the nanoscale as well as with a narrower size distribution are deposited from reversed micellar solutions. Photoelectrochemical experiments show that the effect of Pt morphology on photoconversion efficiency strongly depends on light intensity. At low power of illumination (10 mW/cm2), Pt islands with a mean diameter of 100 nm and a density of 15 particles/microm2, which can be obtained via electroless deposition from a HF-based solution, provide the best photoelectrochemical performance. Nevertheless, this configuration of Pt clusters yields an abrupt collapse of photoconversion efficiency from 31% to 11.8% when the light power is increased up to 100 mW/cm2. At this light intensity, Pt islands with a mean size and density of approximately 40 nm and 75 particles/microm2, respectively, obtained via the microemulsion method, allow photoconversion efficiency as high as 20% to be achieved.     

Stokes flow and deposition of aerosol nanoparticles in model filters composed of elliptic fibers

The calculation is implemented for the fiber collection efficiencies due to diffusion of nanoparticles in model filters, i.e., separate rows of fibers with an elliptic cross section located normal to the flow at different orientations of the ellipse axes with respect to the flow. The Stokes flow field in the system of the fibers is found by the method of fundamental solutions. The concentration field of Brownian particles and the efficiency of their deposition onto the fibers are determined from the numerical solution of the equation for the convective diffusion. The dependence of the capture coefficient on the Peclet number for elliptic fibers is shown to have the form η = APe^−m, where exponent m changes from 2/3 to 3/4 at the parallel and normal orientation of the major axes of the ellipses with respect to the flow, respectively. It is shown that, from the viewpoint of aerosol nanoparticle capture, the best filters are those in which the fibers have a maximum midsection at the same cross-sectional area.     

Deposition of nanoparticles in filters composed of permeable porous fibers

The diffusion deposition of nanoparticles is studied from a flow at low Reynolds numbers in model filters composed of permeable circular porous fibers. The field of particle concentration is calculated and the capture coefficient is determined for a cell, as well as the isolated row of parallel fibers within a wide range of Peclet numbers (Pe) depending on the fiber permeability. It is shown that at Pe > 1, the diffusion capture coefficient η increases with permeability, while at Pe → ∞, it tends toward the limiting value, which is equal to the gas flow rate through the porous fiber. The capture coefficients calculated from a cell model and for a row of fibers are almost equal to each other. The diffusion deposition of aerosol particles in the highest penetration range is calculated with an allowance for their finite sizes and it is shown that the radii of most penetrable particles decrease with an increase in fiber permeability.     

Influence of Gravity on Filtration of Submicron Aerosols of Heavy Metals

Colloid Journal - The influence of gravity on the deposition of high-density submicron aerosol particles in fibrous filters from vertical and horizontal (relative to the gravity vector direction)...     

Diffusional Deposition of Heavy Submicron Aerosol Particles on Fibrous Filters

The deposition of Brownian submicron aerosol particles of high density in fibrous filters with allowance for interception effect, influence of gravitational, van der Waals forces, and the gas slip on the surface of ultrafine fibers was considered. Based on the numerical solution of the equation of convective diffusion in the field of external forces, the capture coefficient was calculated as a function of particle size and density, the angle between the vectors of gravity force, and the face flow velocity. It was shown that, for descending flow, the radius of most penetrating dense particles appeared to be noticeably smaller than for the ascending flow.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 352–356.Original Russian Text Copyright © 2005 by Kirsh.     

Aggregate formation and collision efficiency in differential settling

A new method of application of Stokesian dynamics, which can efficiently simulate movements of up to 500 particles with interparticle interactions in reasonable computational times, has been developed for the purpose of investigating particle-cluster aggregation in aqueous systems. The method is applied to monodisperse non-Brownian spherical particles aggregating in differential settling, while repulsive colloidal interaction is presumed to be negligible, so that a minimum separation distance can represent the attractive van der Waals force. The final aggregates formed by this algorithm, composed of 300 primary particles, have a common fractal dimension of approximately 2.0. The computed collision efficiency, defined as the product of a global and a capture efficiency, is about 5.77x10(-3). This value is significantly larger than the collision efficiency of primary particles colliding with an impermeable solid sphere of the same size as the aggregate, illustrating the important interplay between the permeability and the formation of aggregates.     

Effective medium approximation and deposition of colloidal particles in fibrous and granular media

Laminar flow of fluids through fibrous and granular media and deposition of colloidal particles from a liquid suspension are two fundamental phenomena encountered in many industrial applications. An Effective Medium Approximation (EMA) is used to determine the fluid flow permeability and particle capture efficiency of random arrays of cylindrical and spherical collectors. The EMA assumes a model system in which a packing element (a single fiber in the fibrous medium and a single sphere in the granular medium) is surrounded by a fluid envelope and an effective-medium beyond the envelope. It integrates the important features of both the cell models and Brinkman's model. The Stokes equation and Brinkman equation are solved for the fluid envelope and effective medium regions, respectively, to obtain the permeability and close-to-surface velocity field around the collectors. The convective diffusion equation is then solved to determine the particle deposition rate. The analytical expressions for the permeability and particle deposition rate are derived for all possible cases of random packing of uniform and non-uniform cylinders and spheres. Effects of various system properties and operating conditions on deposition of colloidal particles are investigated. The physical or chemical conditions include the properties which affect the magnitude of double layer interaction: the electrolyte concentration and surface potentials, and the property which affects the van der Waals interaction: the Hamaker constant. It was found that the effects of the above properties is much more significant when the surface interactions play more important roles in the particle deposition process, or when the height of the total interaction energy barrier is higher than 5 kBT. Particle deposition becomes virtually impossible when the height of the repulsive energy barrier increases beyond 20 kBT.     

Formulation optimization and in vitro antibacterial ability investigation of azithromycin loaded FDKP microspheres dry powder inhalation

Azithromycin loaded fumaryl diketopiperazine(FDKP) dry powder inhalation was designed and prepared for the treatment of community-acquired pneumonia.The solubility of FDKP and stability of azithromycin solution was investigated.Formulation of azithromycin loaded FDKP microparticle was investigated and optimized by the single factor experiment.High-pressure homogenization and spray drying conditions were also optimized to prepare the particles by spray drying azithromycin dissolved FDKP microparticle suspension at pH 4.5.The in vitro antibacterial efficiency and in vitro dispersion performance was also investigated to confirm the antibacterial efficiency,dispersion and deposition behavers.FDKP/azithromycin mass ratio(3:2) was the optimized formulation of azithromycin loaded FDKP microparticle with the maximal drug loading efficiency.High-pressure homogenization and spray drying conditions were also optimized.The in vitro antibacterial results indicated that only with the antibiotic concentration higher than mutant prevention concentration could totally inhibit the reproduction of bacteria.In vitro dispersion performance of azithromycin loaded FDKP microparticles(AZM@FDKP-MPs) also shows remarkable improvement of dispersion and deposition behavers of AZM.AZM@FDKP-MPs dry powder inhalation as a targeting delivery route has better potential for lung infection treatment.     

Particle deposition onto micropatterned charge heterogeneous substrates: trajectory analysis

A trajectory analysis of particles near a micropatterned charged substrate under radial impinging jet flow conditions is presented to investigate the effect of surface charge heterogeneity on particle trajectory and deposition efficiency. The surface charge heterogeneity is modeled as concentric bands of specified width and pitch having positive and negative surface potentials. The flow distribution is obtained using finite element analysis of the governing Navier-Stokes equations. The particle trajectory analysis takes into consideration the hydrodynamic interactions, gravity, van der Waals and electrostatic double layer interactions. The presence of surface charge heterogeneity on the substrate gives rise to an oscillating particle trajectory near the collector surface due to repulsive and attractive forces. As a result of the coupled effects of hydrodynamic and colloidal forces, the particle trajectories and deposition efficiencies are increasingly affected by surface charge heterogeneity as one moves radially away from the stagnation point. The results indicate that it is possible to render collectors with up to 50% favorable surface fraction completely unfavorable by modifying the ratio of the radial to normal fluid velocity. Utilizing the real favorable area fraction of the collector, the patch model expression for calculating the deposition efficiency is modified for impinging jet flow geometry.     

Research of Silica Particles Dispersion in Polymer Matrix Under Acoustic Levitation

Series of resins consisting different amount of silica particles with different sizes and surface properties were prepared as suspended samples under an acoustic levitator. The resulting composites after curing under irradiation have been investigated. Fracture surface morphologies of the resins were compared to those with same composition prepared in a normal gravity field via scanning electron microscopy. The results showed that except for such factors like particle sizes, surface properties, particles concentration, and monomer viscosity, the microgravity state produced by acoustic levitation could also be an element that affects silica particles dispersion in the resins.     

Supercomputing and supercomputers for science and engineering in general and for chemistry and biosciences in particular

We start by pointing out relationships between production of information, global simulation, and supercomputing, thus placing our research activities in today's society context. Then we detail the evolution in hardware and software for 1CAP, our experimental supercomputer, which we claim to be especially well suited for supercomputing in science and engineering. A preliminary discussion of 1CAP/3090 (our latest experimental effort) is included. Many examples from different disciplines are provided to verify our assertions. We “prove” our point by presenting an example of global supercomputing. Starting with 3 nuclei and 10 electrons, building up to a single water molecule, then to a few hundred, we learn, for example, about Raman, infrared, and neutron scattering; we then move up to a few hundred thousand molecules to analyze particle flow and obstructions; finally we experiment, but only preliminarily, with a few million particles to learn more on nonequilibrium dynamics as in the Rayleigh-Benard systems. In this way, quantum mechanics is overlapped with statistical mechanics and expanded into microdynamics. The entire paper is finally reanalyzed from a different perspective, presenting rather systematically, even if most briefly, our ideas on “modern” computational chemistry, where quantum mechanics is as much needed as fluid dynamics and graphics. In this section the main computational techniques are analyzed in terms of computer programs and their associated flow diagrams to solve the basic equations using parallel supercomputers.     

重力场和电解质浓度对胶体凝聚体分形结构的影响

运用李航等提出的新方法, 克服了DLVO理论中无法理论计算不同电解质浓度下颗粒的表面电位这一困难, 从而可以直接计算出不同电解质浓度下胶体颗粒间的位能. 同时, 还运用胶体颗粒动能的玻耳兹曼分布原理和蒙特卡罗方法来模拟胶体的运动, 并采用非弹性碰撞理论解决了碰撞后凝聚的有效概率问题. 在改进DDA模型的基础上, 成功地建立了以往的模拟中未能建立的重力场中电解质浓度与碰撞凝聚概率间的联系, 结果发现, (1)重力场作用下的凝聚体分形维数随电解质浓度变化的曲线完全不同于无重力条件下的曲线. 无重力作用下, 凝聚结构体分形维数随电解质浓度的变化比较缓慢, 曲线呈“L”形；而重力作用下的分形维数则呈明显的“S”形曲线. (2) 在重力条件下, 慢凝聚包括两个区域, 对电解质浓度不敏感区域和敏感区域. 在敏感区域存在一个电解质浓度的拐点. (3)无重力条件下,不同大小的胶体颗粒在快凝聚时的分形维数都是在1.86±0.01.当电解质浓度降低,凝聚速率变慢,分形维数增加,最大达到2.01±0.02,但不会形成重力条件下的分形维数接近3的结构体.     

Surface chemicals concepts of flotation de-inking

This review outlines the important parameters, which influence the flotation de-inking and discusses the surface chemical aspects of the process. Although, it has been established increasing temperature and pH facilitate the release of ink particles from the fibre during pulping (prior to flotation), it has not yet been completely established to what extent these parameters increase or decrease the efficiency of the primary flotation step. In fact, increasing temperature appears to decrease the flotation rate and also an increase in pH can retard the flotation due to a reduction in capture efficiency between the air bubbles and the ink particles decreasing the flotation in the cell. In addition, the size, shape and roughness of the ink particles influence this bubble/particle capture mechanism. Bubble frequency and bubble size is influenced by surface tension (type and concentration of frother) but X-ray studies also indicate that the fibre consistency can influence the bubble shape and flow patterns causing channelling and re-circulation of bubble flow in the cell. Tests with different gases (oxygen and nitrogen instead of air) show no significant gains in optical and mechanical properties of the fibre. Fatty acids with higher chain length and lower degree of saturation are less soluble and ensure lower carry-over but less foaming and also less fibre recovery. The primary mechanisms of fatty acid flotation involves precipitation of calcium soap, followed by micro-encapsulation of ink through a hetero-coagulation mechanism, followed by the bubble/ink particle capture step. In the use of nonionic surfactant, cloud point and HLB are important parameters, which influence brightness, washing and flotation efficiency. Optimum flotation occurs with slight excess of fatty acid to reduce surface tension and optimum calcium levels ensuring that most of the calcium is removed in the process. A lower calcium level gives lower stock loss but a high calcium has a detrimental effect, causing scaling and deposition. A critical nonionic/fatty acid balance is needed to minimize stock loss during the flotation. New chemicals need to be developed to increase selectivity, reduce entrainment and increase the process efficiency. Also, the underlying knowledge linking structural/function relationship for de-inking chemicals in relationship to the heterogenity at the pulps needs to be established. Further progress could help in the treatment of higher fibre content pulps, reducing water and chemical consumption and reducing redeposition of the ink on the fibre.     

Deposition efficiency of fractal-like aggregates in fibrous filters calculated using Brownian dynamics method

Nonspherical particles, such as fractal-like aggregates emitted by diesel engines, are commonly met in the ambient air. Some of them are believed to be carcinogenic to humans, thus their efficient removal is of crucial practical importance. A fibrous filter is the device commonly used for aerosol purification but the literature lacks experimental data concerning aggregates filtration. Effect of aggregates' parameters (fractal dimension, primary particle radius) as well as fiber diameter and air velocity on the filtration efficiency is investigated theoretically using the modified Brownian dynamics method. Three different expressions for the friction coefficient evaluation for the aggregates were examined. The results obtained indicate that structure of an aggregate, filter structure and process conditions strongly influence the aggregates deposition efficiency, which significantly differs from the values determined for mass-equivalent spherical particles. The results determined using the Brownian dynamics approach were compared with the values calculated using classical single fiber theory and noticeable discrepancy was observed for the most penetrating particles, while both approaches agree for the limiting cases of small or large particles. Peclet number based on the mobility radius and the interception parameter based on the outer radius are the proper criteria to describe diffusional and deterministic deposition of aggregates.     

Analysis of therapeutic effectiveness attained through generation of three alpha particles in proton-boron fusion reaction based on Monte Carlo simulation code

This study analyzed the effectiveness attained through generation of three alpha particles in proton-boron fusion therapy (PBFT) based on a Monte Carlo simulation. PBFT is based on a fusion reaction between protons and boron. Three alpha particles are emitted from this reaction. The three alpha particles cause greater damage to tumor cells than the single alpha particle produced in the boron neutron capture reaction or conventional therapy. In addition, the intrinsic proton dose pattern follows Bragg-peak curve. We confirmed an energy deposition by the alpha particle and verified the therapeutic effect of the PBFT.