Mobility of nanofiber, nanorod, and straight-chain nanoparticles in gases

Abstract

With the fast development of nanotechnology, accurate measurement and classification of nanoparticles are in great need. Nanoparticles frequently appear in non-spherical forms such as long aspect ratio nanofibers, nanotubes, and irregular nano-agglomerates. While the welldeveloped classical studies were mainly in continuum regime with spherical particles, dynamics of the non-spherical nanoparticles is not fully understood. In this study, orientation-averaged mobility of nanofiber and nanorod (with no preferred alignment) is examined by the methods of Brownian diffusion theory, a combination of collision limited reaction rate theory and the bipolar diffusion charging analysis. Comparisons to empirical predictions from the experimental measurements are also made. The study leads to the discovery of a surface-dominated mobility for high aspect ratio nanoparticles with characteristic Knudsen number greater than 5. In view of the extreme relative length scales between particle size and the gas mean free path, particles of all morphologies can be viewed as point collisions; therefore, the equivalent surface mobility diameter is reasonably justified. This finding has been verified in the current study with high aspect ratio particles. For non-spherical particles of more general forms, further investigation is needed. As expected, accuracy of this approximation reduces as the characteristic Knudsen number decreases. When Kn(d L ) < 0.1, the study shows that particle morphology starts to play an important role. A review of particle mobility for all Knudsen number flows is also provided.

Morphology-Invariant Metallic Nanoparticles with Tunable Plasmonic Properties

“…In conventional overgrowth-based systems, the strategy was to grow Ag on the outer surfaces of a seed. , To compare the efficiencies of these two different strategies in tuning LSPR properties, we designed a set of experiments. Specifically, ∼ 58 nm Au nanospheres (Figure S12a) and ∼37 × 90 nm Au nanorods (Figure S13a) that have similar surface areas as the inner surfaces of 48 nm Ag–Au cages (Figure b) and similar volume equivalent diameters (which is defined as the diameter for a sphere with the same volume as a particle with a nonspherical shape , ) as the cages were prepared. These three types of seeds with similar extinction intensities were grown with the same amounts of Ag through the reduction of AgNO 3 by AA (see details in Figure a and Methods).…”

Computational modeling of fiber transport in human respiratory airways—A review

“…Assuming a randomized distribution of fiber orientation in the simplified Eulerian-Lagrangian (E-L) approach, shearinduced lift and Brownian diffusion force were frequently calculated by using the formulas of volume-equivalent spherical particles in literature. Using the fiber mobility equivalent sphere, Tian et al (2017) studied the fiber dispersion in inertial and high Knudsen number flows. Based on their study, an aerodynamic (or Stokes diameter) for the inertia flow and a surface equivalent diameter (or projected surface equivalent) diameter for the high Knudsen number flow should be used to characterize the fiber motion, respectively.…”

“…Instead of the equivalent Stokes diameters, the deposition results of the nanofibers correlated closely to the Peclet number. Tian et al ( , 2017 presented a detailed comparison of the various equivalent diameters in characterizing nanofiber dynamics. While they identified the surface dominated transport mechanisms as most pertinent to the high Knudsen number flows, the application of these findings to deposition in tracheobronchial airways has yet to be reported.…”

“…Tian et al (2012) reported the transport and deposition of ellipsoidal fibers in low Reynolds number pipe flow, where details of the fiber rotational motion were analyzed. Focusing on the fiber molecular diffusion, Tian et al ( , 2017 developed the semi-empirical governing equations for fiber diffusion and studied the isotropic and anisotropic diffusion properties of ellipsoidal fibers. In addition, they evaluated the orientational independent fiber equivalent spheres.…”

Homogeneous and Multiphase Analysis of Nanofluids Containing Nonspherical MWCNT and GNP Nanoparticles Considering the Influence of Interfacial Layering

“…The is the Cunningham correction factor of the spherical nanoparticles. The modified Cunningham correction factors for cylindrical (MWCNT) and thin-disc (GNP)-shaped nanoparticles are given in Equations(49) and (50)[56], respectively.= 3 [ (2 ) − 0.72] 2…”