Fluid Particle Accelerations in Fully Developed Turbulence

The motion of fluid particles as they are pushed along erratic trajectories by fluctuating pressure gradients is fundamental to transport and mixing in turbulence. It is essential in cloud formation and atmospheric transport, processes in stirred chemical reactors and combustion systems, and in the industrial production of nanoparticles. The perspective of particle trajectories has been used successfully to describe mixing and transport in turbulence, but issues of fundamental importance remain unresolved. One such issue is the Heisenberg-Yaglom prediction of fluid particle accelerations, based on the 1941 scaling theory of Kolmogorov (K41). Here we report acceleration measurements using a detector adapted from high-energy physics to track particles in a laboratory water flow at Reynolds numbers up to 63,000. We find that universal K41 scaling of the acceleration variance is attained at high Reynolds numbers. Our data show strong intermittency---particles are observed with accelerations of up to 1,500 times the acceleration of gravity (40 times the root mean square value). Finally, we find that accelerations manifest the anisotropy of the large scale flow at all Reynolds numbers studied.Comment: 7 pages, 4 figure

Facile meltPEGylation of flame-made luminescent Tb3+-doped yttrium oxide particles: hemocompatibility, cellular uptake and comparison to silica

Flame aerosol technology is a versatile method for scalable synthesis of nanoparticles. Since particles are produced and collected in a dry state, dispersibility and further functionalization could pose hurdles to their biomedical use. We report on a one-pot, scalable and robust procedure for the PEGylation of flame-made yttria and silica nanoparticles. We demonstrate improved colloidal stability, attenuated activation of blood coagulation and decreased uptake into phagocytic cells, all of which pave the way for facilitated biomedical use of flame-made oxide nanoparticles

Biocompatibility and Bone Formation of Flexible, Cotton Wool-like PLGA/Calcium Phosphate Nanocomposites in Sheep

BACKGROUND: The purpose of this preliminary study was to assess the in vivo performance of synthetic, cotton wool-like nanocomposites consisting of a biodegradable poly(lactide-co-glycolide) fibrous matrix and containing either calcium phosphate nanoparticles (PLGA/CaP 60:40) or silver doped CaP nanoparticles (PLGA/Ag-CaP 60:40). Besides its extraordinary in vitro bioactivity the latter biomaterial (0.4 wt% total silver concentration) provides additional antimicrobial properties for treating bone defects exposed to microorganisms. MATERIALS AND METHODS: Both flexible artificial bone substitutes were implanted into totally 16 epiphyseal and metaphyseal drill hole defects of long bone in sheep and followed for 8 weeks. Histological and histomorphological analyses were conducted to evaluate the biocompatibility and bone formation applying a score system. The influence of silver on the in vivo performance was further investigated. RESULTS: Semi-quantitative evaluation of histology sections showed for both implant materials an excellent biocompatibility and bone healing with no resorption in the adjacent bone. No signs of inflammation were detectable, either macroscopically or microscopically, as was evident in 5 µm plastic sections by the minimal amount of inflammatory cells. The fibrous biomaterials enabled bone formation directly in the centre of the former defect. The area fraction of new bone formation as determined histomorphometrically after 8 weeks implantation was very similar with 20.5 ± 11.2 % and 22.5 ± 9.2 % for PLGA/CaP and PLGA/Ag-CaP, respectively. CONCLUSIONS: The cotton wool-like bone substitute material is easily applicable, biocompatible and might be beneficial in minimal invasive surgery for treating bone defects

The capacitance and charge of agglomerated nanoparticles during sintering

University of Minnesota Ph.D. dissertation. December 2017. Major: Mechanical Engineering. Advisor: David Pui. 1 computer file (PDF); xi, 123 pages.This thesis consists of two parts: unipolar diffusion charging of nanoparticles and its application on the method development of surface-area measurements. The electrical capacitance of aerosol particles indicates their potential diffusion charging level, which is important for their classification by electrical mobility, precipitation (removal or collection) in electrical fields, and morphology characterization. A minimum potential energy method was used to calculate the electrical capacitance for agglomerates composed of equally sized spherical primary particles (PPs). By discretizing the particle surface using finite spherical elements, as net charge only resides on the surface of an isolated conductor, this method was extended to calculate the capacitance of arbitrarily shaped particles. Based on the capacitance, the charge of these particles was obtained by diffusion charging theory. In addition, the dynamics of capacitance and mean charge of agglomerate during sintering or coalescence (at constant particle volume) to aggregates and finally to compact structures was computed and found in agreement with sparse experimental data. Particle morphology strongly affects the capacitance and mean charge of fractal-like particles. For example, both decreased by 60% upon full coalescence or sintering of an agglomerate consisting initially of 128 PPs. Although geometric surface area (GSA) of nanoparticles has received much attention in many fields (drug delivery, catalysts, inhalation exposure, toxicity, etc.), no appropriate instruments and methods for online measurements of GSA are readily available. Therefore, this study intends to develop a Geometric Surface Area Monitor (GSAM) to measure the GSA of spherical as well as model agglomerate/aggregate nanoparticles in nearly real-time. The GSAM has two versions: 1. The GSAM (I) consists of several existing techniques in series, including inertial impaction, unipolar charging, electrostatic precipitation, and electrical current measurement. The GSAM (I) was first evaluated and calibrated by measuring the GSA of monodisperse nanoparticles. Spherical, aggregate, and agglomerate nanoparticles were tested in the calibration. It was found that the measured electrical current was proportional to the surface area concentration. The calibration curves obtained from the measurements of monodisperse particles was then applied for polydisperse spherical particles and compared the measured GSA with that determined by the well-known scanning mobility particle sizer (SMPS) where the GSAM (I) had less than 10% of deviation compared with SMPS. 2. In the GSAM (II), the commercialized nanoparticle surface area monitor was used and slightly modified. The instrument responses under two different conditions were combined in a weighted sum (WS) fashion to correlate with the aerosol GSA concentration. We present the GSA concentration results and comparisons with well-known SMPS data in both laboratory testing and field measurement. For the laboratory testing, the two methods have a good agreement with a Pearson correlation coefficient of 0.9961; for the field measurements including the indoor and outdoor samplings, both methods agree well with each other. In addition, the new WS method is more stable in the clean indoor air and suitable for outdoor environmental sampling with a slight overestimation (125% of SMPS). These three studies below comprise parts of the main body of this dissertation and have been published. Chapter 2: Cao, L. N. Y., Wang, J., Fissan, H., Pratsinis, S. E., Eggersdorfer, M. L., & Pui, D. Y. H. (2015). The capacitance and charge of agglomerated nanoparticles during sintering. Journal of Aerosol Science, 83(0), 1-11. doi: http://dx.doi.org/10.1016/j.jaerosci.2015.01.002 Chapter 3: Cao, L. N. Y., Chen, S.-C., Fissan, H., Asbach, C., & Pui, D. Y. H. (2017). Development of a geometric surface area monitor (GSAM) for aerosol nanoparticles. Journal of Aerosol Science, 114, 118-129. doi: https://doi.org/10.1016/j.jaerosci.2017.09.013 Chapter 4: Cao, L. N. Y. & Pui, D. Y. H. A novel weighted sum method to measure particle geometric surface area in real-time, Journal of Aerosol Science, doi: https://doi.org/10.1016/j.jaerosci.2017.12.00

Hermetically-coated superparamagnetic Fe<inf>2</inf>O<inf>3</inf> particles with SiO<inf>2</inf> nanofilms

Magnetic nanoparticles are frequently coated with SiO2to improve their functionality and bio-compatibility in a range of biomedical and polymer nanocomposile applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coaled with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis (FSP) of iron acelylacetonale in xylene/acetonitrile solutions, and the resulting aerosol was in situ coaled with SiO2 by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe2O3, particle properties and the thickness of their silica coaling film. This ensures that the non-magnetic SiO2 layer can be closely controlled and minimized. The optimal SiO2 content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe2O3 coated with about 2 nm thin SiO2 layers was nearly identical lo that of uncoated, pure Fe2O3 nanoparlicles