Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session M36: Nano Flows II |
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Chair: Sindy Tang, Stanford University Room: Alcove A |
Tuesday, November 25, 2014 8:00AM - 8:13AM |
M36.00001: Viscoelastic Flows in Simple Liquids Generated by Vibrating Nanostructures John Sader, Matthew Pelton, Debadi Chakraborty, Edward Malachosky, Philippe Guyot-Sionnest Newtonian fluid mechanics, in which the shear stress is proportional to the strain rate, is synonymous with the flow of simple liquids like water. We report the measurement and theoretical verification of non-Newtonian, viscoelastic flow phenomena produced by the high-frequency ($>$20 GHz) vibration of gold nanoparticles immersed in water-glycerol mixtures. The observed viscoelasticity is not due to molecular confinement, but is a bulk continuum effect arising from the short time scale of vibration. This represents the first direct mechanical measurement of the intrinsic viscoelastic properties of simple bulk liquids, and opens a new paradigm for understanding extremely high frequency fluid mechanics, nanoscale sensing technologies, and biophysical processes. [Preview Abstract] |
Tuesday, November 25, 2014 8:13AM - 8:26AM |
M36.00002: Nanofluid Flow and Heat Transfer in Channel Entrance Region Joseph T.C. Liu, Gianluca Puliti The present work uses the continuum description of nanofluid flow to study the flow, heat and mass transfer in the entrance and developing region of channels or tubes, where the viscous and heat conduction layers are thin and the heat transfer is much more intense than fully developed flow. Instead of supplementing the formulation with thermodynamic properties based on mixture calculations, use is made of recent molecular dynamical computations of such properties, specifically, the density and heat capacity of gold-water nanofluids. The more general formulation results, within the Rayleigh-Stokes (plug flow) approximation and perturbation for small volume fraction, show that the nanofluid density-heat capacity has an enormous effect in the inertia mechanism in causing the nanofluid temperature profile to steepen. The nanofluid thermal conductivity though has an explicit enhancement of the surface heat transfer rate has the almost hidden effect of stretching the nanofluid temperature profile thus giving the opposite effect of enhancement. Quantitative results for Gold-Water nanofluid is presented. [Preview Abstract] |
Tuesday, November 25, 2014 8:26AM - 8:39AM |
M36.00003: Microscopic Description of Resonance in the Brownian Motion of Hydrophobic Nanoparticle in Harmonic Potential Trap Jae Hyun Park Harmonic potential has been popular for the trapping of micro- and nanoparticles (e.g. optical tweezer). With the rapid development of harmonic potential trapping technology, its application is nowadays being extended to explore the fundamental nature in the random thermal fluctuation of particles in order to confirm the classical theory of Brownian motion. In this study, using extensive molecular dynamics simulations, we investigate the molecule-level features of dynamic response of hydrophobic C$_{60}$ nanoparticle in harmonic potential trap with water medium. The time-averaged magnitudes of random fluctuation are measured for various trap stiffness and then the virtual mass, the amount of fluid moving together with particle, is extracted from curve fitting. The fluctuation is proportional to the inverse of trap stiffness. The virtual mass is mostly originated from the first hydration shell around the particle and it is not influenced by the stiffness. The resonance in frequency domain is observed as a result of coloured noise in the motion. The effect of stiffness on the resonance is weaker than that on the magnitude of fluctuation because the motion of particle is partially dissipated in the RDF valley between the first and the second hydration shell. [Preview Abstract] |
Tuesday, November 25, 2014 8:39AM - 8:52AM |
M36.00004: Translational and rotational diffusion of a single Janus nanoparticle in an explicit solvent Ali Kharazmi, Nikolai Priezjev Molecular dynamics simulations are carried out to study the translational and rotational diffusion of a Janus particle in a Lennard-Jones fluid. We consider a spherical particle with two hemispheres of different wettability. The analysis of the particle dynamics is based on the time-dependent orientation tensor, particle displacement, as well as the translational and angular velocity autocorrelation functions. We show that both translational and rotational diffusion coefficients increase with decreasing surface energy at the nonwetting hemisphere. It was found that in contrast to uniform particles, the nonwetting hemisphere of the Janus particle rotates in the direction of the displacement vector during the rotational relaxation time. [Preview Abstract] |
Tuesday, November 25, 2014 8:52AM - 9:05AM |
M36.00005: Improved Proper Orthogonal Decomposition for Noise Reduction in Particle Flow Simulations Malgorzata Zimon, Leopold Grinberg, Jason Reese, David Emerson Proper orthogonal decomposition (POD), widely utilised for turbulent flows, has recently been explored for processing particle data. An extension of the method based on time-windows offers a useful approach for noise reduction in particle simulations. However, to successfully remove statistical noise from the system, large amounts of data need to be provided. Moreover, POD can fail to improve the quality of an ensemble mean (statistical average) when applied to steady-state simulations. In order to achieve a better efficiency of POD in processing non-stationary fields, we have combined the method with wavelet-based filtering. In this new procedure, the wavelet thresholding is performed within POD's domain. In case of stationary problems, we will show how effectively POD can be applied to a matrix constructed from the mean, following the application of singular spectral analysis (SSA). The combination of POD and SSA is shown to successfully smooth time-dependent observables. Simulations were undertaken to illustrate the performance of the new tools applied to noisy velocity and density fields. Numerical examples include molecular dynamics, dissipative particle dynamics simulations of force-driven fluid flows and phase separation phenomena. [Preview Abstract] |
Tuesday, November 25, 2014 9:05AM - 9:18AM |
M36.00006: The filtration of colloidal gold nanopartilces in nanoporous media Franciscus de Jong, Michael Schlueter Deep-bed filtration is connected to a wide variety of disciplines ranging from biology and medicine to engineering. A novel material with promising perspectives that can be used for deep-bed filtration are forests consisting of numerous multi-walled carbon nanotubes (MWCNTs). The filtration kinetics of particles within deep-beds is usually addressed using global investigations (i.e. the concentration of particles in the bulk solution). However, to optimize MWCNT forests for filtration purposes detailed information of the local filtration kinetics is indispensible. In the study presented here microbeam small-angle X-ray scattering (muSAXS) is used, for the first time, to study both, the spatial and the temporal local filtration kinetics of small-sized particles within MWCNT forests. The filtration is (globally) verified based on (I) scanning electron microscopy and (II) inductively coupled plasma atomic emission spectroscopy (ICP-AES). Good agreement is observed between the local and the global measurements (i.e. a difference of 4.3{\%}). The use of muSAXS to understand the local filtration kinetics of submicrometer particles opens up pathways to effectively optimize functionalized MWCNT forests and prepare them for specific filtering purposes. [Preview Abstract] |
Tuesday, November 25, 2014 9:18AM - 9:31AM |
M36.00007: Static and Alternating Field Magnetic Capture and Heating of Iron Oxide Nanoparticles in Simulated Blood Vessels Joanne Haeun Lee, Rhythm R. Shah, Christopher S. Brazel Targeted drug delivery and localized hyperthermia are being studied as alternatives to conventional cancer treatments, which can affect the whole body and indiscriminately kill healthy cells. Magnetic nanoparticles (MNPs) have potential as drug carriers that can be captured and trigger hyperthermia at the site of the tumor by applying an external magnetic field. This study focuses on comparing the capture efficiency of the magnetic field applied by a static magnet to an alternating current coil. The effect of particle size, degree of dispersion, and the frequency of the AC field on capture and heating were studied using 3 different dispersions: $16$ nm maghemite in water, $50$ nm maghemite in dopamine, and 20-30 nm magnetite in dimercaptosuccinic acid. A 480G static field captured more MNPs than a similar 480G AC field at either 194 or 428 kHz; however, the AC field also allowed heating. The MNPs in water had a lower capture and heating efficiency than the larger, dopamine-coated MNPs. This finding was supported by dynamic light scattering data showing the particle size distribution and vibrating sample magnetometry data showing that the larger MNPs in the dopamine solution have a higher field of coercivity, exhibit ferrimagnetism and allow for better capture while smaller (16 nm) MNPs exhibit superparamagnetism. The dispersions that captured the best also heated the best. [Preview Abstract] |
Tuesday, November 25, 2014 9:31AM - 9:44AM |
M36.00008: Pore dynamics in a liquid membrane Alexander Nepomnyashchy, Vladimir Volpert It is known that vesicles formed from lipid bilayer membranes are used for transportation of a toxic drug to a target, where the drug is released by pore creation. The pores in a membrane show a rather nontrivial dynamics, which thus far has been studied by means of simplified models. In the present talk, we describe the pore dynamics in a stretched membrane, which is considered as a two-dimensional viscous or viscoelastic liquid medium surrounded by a three-dimensional ambient viscous liquid. In the case of a viscoelastic membrane, a Lagrangian approach, which allows to account for large displacements, is applied. A closed equation for the pore radius is derived and investigated. [Preview Abstract] |
Tuesday, November 25, 2014 9:44AM - 9:57AM |
M36.00009: Effect of nanostructures and electrostatic interactions on disjoining pressure of ultra-thin liquid film Han Hu, Christopher Weinberger, Ying Sun Disjoining pressure, the excess pressure that stems from the long-range intermolecular interactions, plays a key role in the stability of thin films in applications such as lubrication, wetting, boiling, condensation and evaporation. In recent years, nanostructures have been introduced as a means to control the stability of thin films. However, the classic theory of disjoining pressure assumes atomically smooth surface and neglects the electrostatic interactions. In the present study, the effect of nanostructures and electrostatic interactions on disjoining pressure is examined with combined modeling and molecular dynamics simulations. A model of meniscus shape and disjoining pressure for a thin liquid film on a nanostructured surface is derived based on minimization of system free energy and Derjaguin approximation. The scaled healing length $\xi /D$ ($D$ the nanostructure depth) is used to characterize the competition between the liquid surface tension and solid-liquid intermolecular forces. The result shows disjoining pressure increases with $D$. The model prediction agrees well with molecular dynamics simulations for a water-gold system. The electrostatic interactions enhance the disjoining pressure effect but the strength of the electrostatic interactions becomes weaker as the aspect ratio of the nanostructures increases. [Preview Abstract] |
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