Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session B20: Focus Session: Microfluidics and Nanofluidics II - Colloidal Hydrodynamics and Active Particles |
Hide Abstracts |
Sponsoring Units: DPOLY GSNP DFD Chair: Steven Hudson, National Institute of Standards and Technology Room: 405 |
Monday, March 3, 2014 11:15AM - 11:27AM |
B20.00001: The Role of Inertia in Particle Laden Flows Hamed Haddadi, Jeffrey Morris The microstructure and rheological properties of suspensions of neutrally buoyant hard spherical particles under finite inertia are studied using lattice-Boltzmann method (LBM). The suspensions are subjected to simple shear flow and the properties are studied as a function of inertia and volume fraction, ?. The inertia is characterized by shear flow Reynolds number, Re. The influence of inertia and the volume fraction is studied for 0.005 < Re < 2 and 0.1 < ? < 0.3. The topology of the streamlines and pair trajectories, specially off-plane configurations, are observed in more detail. The flow induced microstructure is investigated using the pair distribution function g(r). Different stress types generated by surface tractions, acceleration and velocity fluctuations are computed and their influence on the first and second normal stress differences, the particle pressure and the viscosity of the suspensions are detailed. In addition, the dynamics of the particle interactions are examined from a pair kinematics perspective. One specific example of inertia flow in a microfluidic set up is briefly discussed. [Preview Abstract] |
Monday, March 3, 2014 11:27AM - 11:39AM |
B20.00002: Hydrodynamic Fluctuations in Confined Particle-Laden Fluids Nicolas Desreumaux, Jean-Baptiste Caussin, Raphael Jeanneret, Eric Lauga, Denis Bartolo We address the collective dynamics of non-Brownian particles cruising in a confined microfluidic geometry and provide a comprehensive characterization of their spatiotemporal density fluctuations. We show that density excitations freely propagate at all scales, and in all directions even though the particles are neither affected by potential forces nor by inertia. We introduce a kinetic theory which quantitatively accounts for our experimental findings, demonstrating that the fluctuation spectrum of this nonequilibrium system is shaped by the combination of truly long-range hydrodynamic interactions and local collisions. We also demonstrate that the free propagation of density waves is a generic phenomenon which should be observed in a much broader range of hydrodynamic systems. [Preview Abstract] |
Monday, March 3, 2014 11:39AM - 11:51AM |
B20.00003: Microscopic origin of drag force: A new mathematical and physical interpretation Changho Kim, George Karniadakis We present a new microscopic interpretation of the friction force on a Brownian particle of finite mass suspended in a fluid: it originates from the deviation of the system trajectory due to the movement of the particle. We perform a systematic theoretical investigation on the observation that compared with the frozen dynamics of the fluid where the Brownian particle is fixed, the movement of the Brownian particle perturbs the trajectory of the fluid particles and correspondingly the force on the Brownian particle. We show that as the mass $M$ of the Brownian particle increases, the drag force becomes the ensemble average of the force deviation over the fluid configurations, whereas the thermal noise due to the fluctuation of the fluid becomes the force in the frozen dynamics. In addition, we obtain asymptotic expansions (with respect to $M$) of the friction force and thermal noise defined by the memory function and derive several expressions for single-particle Brownian motion near the Brownian limit. We perform a molecular dynamics simulation study on the Rayleigh model (i.e., a Brownian particle in an ideal gas), which provides a clear validation of the theory. We also observe the skewness in the force distributions and the bath-particle density on the simulation. [Preview Abstract] |
Monday, March 3, 2014 11:51AM - 12:03PM |
B20.00004: Defect Proliferation in Active Nematic Suspensions Prashant Mishra, Mark J. Bowick, Luca Giomi, M. Cristina Marchetti The rich structure of equilibrium nematic suspensions, with their characteristic disclination defects, is modified when active forces come into play. The uniform nematic state is known to be unstable to splay (extensile) or bend (contractile) deformations above a critical activity. At even higher activity the flow becomes oscillatory and eventually turbulent. Using hydrodynamics, we classify the active flow regimes as functions of activity and order parameter friction for both contractile and extensile systems. The turbulent regime is marked by a non-zero steady state density of mobile defect pairs. The defect density itself scales with an ``active Ericksen number,'' defined as the ratio of the rate at which activity is injected into the system to the relaxation rate of orientational deformations. [Preview Abstract] |
Monday, March 3, 2014 12:03PM - 12:15PM |
B20.00005: Aggregation and segregation of confined self-propelled particles Xingbo Yang, M. Lisa Manning, M. Cristina Marchetti We study the effect of confinement on a collection of self-propelled (SP) disks in two dimensions, interacting solely via soft elastic repulsion. Individual SP particles perform persistent random walks characterized by the self-propulsion speed v$_{\mathrm{0}}$ and the rotational diffusion rate. In a single component system, we observe spontaneous aggregation of particles at the walls at low packing fraction when their persistence length is smaller than the system size. Above the packing fraction where jamming occurs in passive disks, collective effects become important and a finite v$_{\mathrm{0}}$ is needed for aggregation. The pressure on the wall shows a non-monotonic dependence on packing fraction: a linear growth consistent with ideal gas behavior at small packing fraction and a decrease at large packing fraction. In a bidisperse system of disks with radii ratio 1 : 1.4 we find spontaneous species segregation. This arises from the interplay of self propulsion and the asymmetry in the elastic energy barriers seen by different-sized particles during collisions. [Preview Abstract] |
Monday, March 3, 2014 12:15PM - 12:27PM |
B20.00006: Quantitative kinetic theory of active matter Thomas Ihle, Yen-Liang Chou Models of self-driven agents similar to the Vicsek model [Phys. Rev. Lett. 75 (1995) 1226] are studied by means of kinetic theory [1,2]. In these models, particles try to align their travel directions with the average direction of their neighbours. At strong alignment a globally ordered state of collective motion forms. An Enskog-like kinetic theory is derived from the exact Chapman-Kolmogorov equation in phase space using Boltzmann's mean-field approximation of molecular chaos. The kinetic equation is solved numerically by a nonlocal Lattice-Boltzmann-like algorithm. Steep soliton-like waves are observed that lead to an abrupt jump of the global order parameter if the noise level is changed. The shape of the wave is shown to follow a novel scaling law and to quantitatively agree within 3 \% with agent-based simulations at large particle speeds. This provides a mean-field mechanism to change the second-order character of the flocking transition to first order. Diagrammatic techniques are used to investigate small particle speeds, where the mean-field assumption of Molecular Chaos is invalid and where correlation effects need to be included. [1] T. Ihle, Phys. Rev. E 83 (2011) 030901; 88 (2013) 040303. [2] Y.L. Chou et al, Phys. Rev. E 86, 021120 (2012). [Preview Abstract] |
Monday, March 3, 2014 12:27PM - 12:39PM |
B20.00007: Mixing in suspensions of active particles Dmitri O. Pushkin, Julia M. Yeomans Microscopic active particles self-propelling in the surrounding fluid create flows that eventually lead to emergence of non-equilibrium states with long-ranged fluctuations. One of the technologically important consequences of these fluctuations is enhanced mixing of the surrounding fluid. It is also critical for understanding the ecology of a particular type of biological active systems, bacterial suspension, as the enhanced mixing strongly alters the fluxes of nutrients. We consider the theoretical foundations of fluid mixing enhancement in dilute suspensions of active force-free swimmers. We describe the impediments to fluid mixing imposed by the physical nature of fluid flows created by swimmers, and different ways of overcoming them. We show that fluid mixing in 3D suspensions of force-free (dipolar) swimmers is dominated by the effect of curvature of their trajectories, and obtain an exact analytical expression for the corresponding effective diffusion coefficient. Our results highlight limitations of alternative ``effective temperature'' approaches and may serve as a quantitative tool for designing technological applications. [Preview Abstract] |
Monday, March 3, 2014 12:39PM - 12:51PM |
B20.00008: Rotational manipulation of plasmonic nanoparticles in water by photon angular momentum Peter Johansson, Anni Lehmuskero, Robin Ogier, Tina Gschneidtner, Mikael Kall A photon carries energy, momentum and angular momentum, and can transfer each of these properties to material objects. It is well-known that optical gradient and radiation pressure forces caused by a focused laser beam enables trapping and manipulation of objects with strength dependent on the particle's optical properties. Moreover, the transfer of photon spin angular momentum, makes it possible to set objects into rotational motion by targeting them with a beam of circularly polarized light. We show that this effect can set $\sim$200 nm radii gold particles trapped in water in 2D by laser tweezers into rotation at frequencies that reach several kilohertz, much higher than any previously reported light driven rotation of a microscopic object, but still at low Reynolds numbers [1]. We also derive a theory for the fluctuations in light scattering from a rotating particle, and we argue that the high rotation frequencies observed experimentally is the combined result of favorable optical particle properties and a low local viscosity due to substantial heating of the particles surface layer. The high rotation speed suggests possible applications in nanofluidics, optical sensing, and microtooling of soft matter. \\[4pt] [1] A. Lehmuskero, {\it et al.}, Nano Lett.\ {\bf 13}, 3129 (2013). [Preview Abstract] |
Monday, March 3, 2014 12:51PM - 1:03PM |
B20.00009: Effective Interactions in Systems of Active Particles Matthew Spellings, Michael Engel, Daphne Klotsa, Wenbo Shen, Greg van Anders, Sharon C. Glotzer Systems of linearly-driven active particles have been shown to exhibit fluid-solid coexistence in experiments and simulations. Still, the behavior of these and rotationally-driven anisotropic particles remains open for exploration. In this talk, we show that the addition of a constant driving torque for each particle to form an active system has a nonlinear effect on emergent forces between particles, which can be tuned to be attractive or repulsive. Effective interactions due to activity are naturally switchable and give us a new, orthogonal design dimension for assembly engineering in addition to more traditional design variables such as particle shape and enthalpic patchiness. [Preview Abstract] |
Monday, March 3, 2014 1:03PM - 1:15PM |
B20.00010: ABSTRACT MOVED TO S15.00014 |
Monday, March 3, 2014 1:15PM - 1:27PM |
B20.00011: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 1:27PM - 1:39PM |
B20.00012: Correlation between rotational and translational diffusion of a Janus nanoparticle in explicit solvent: A molecular dynamics simulation study Ali Kharazmi, Nikolai Priezjev Molecular dynamics simulations are used to study the diffusion of a single Janus particle immersed in a Lennard-Jones fluid. We consider a spherical particle with two hemispheres of different wettability. We analyzed the time dependence of the orientation tensor, particle displacement, and translational and rotational velocity autocorrelation functions. It was found that both translational and rotational diffusion coefficients increase with decreasing surface energy of the nonwetting hemisphere. We also observed that in contrast to homogeneous particles, the nonwetting hemisphere of the Janus particle tends to rotate in the direction of the displacement vector during the rotational relaxation time. Financial support from NSF (CBET-1033662) is gratefully acknowledged. [Preview Abstract] |
Monday, March 3, 2014 1:39PM - 1:51PM |
B20.00013: Diffusion of Interacting Particles in Discrete Geometries Kwinten Nelissen, T. Becker, Bart Cleuren, B. Partoens, C. Van den Broeck We evaluate the self-diffusion and transport diffusion of interacting particles in a discrete geometry consisting of a linear chain of cavities, with interactions within a cavity described by a free-energy function. Exact analytical expressions are obtained in the absence of correlations, showing that the self-diffusion can exceed the transport diffusion if the free-energy function is concave. The effect of correlations is elucidated by comparison with numerical results. Quantitative agreement is obtained with recent experimental data for diffusion in a nanoporous zeolitic imidazolate framework material, ZIF-8. [Preview Abstract] |
Monday, March 3, 2014 1:51PM - 2:03PM |
B20.00014: Applying Inkjet Technology to Dispense Colloidal Nanoparticle Fluids Annie O, Harjyot Mohar, Victor Hernandez, Arturo Estrada, Leonel Munoz, Sewan Fan, Laura Fatuzzo, Steven Jimenez The inkjet technology is widely employed to reliably deliver nanomaterials onto a substrate medium for further characterization and processing. To explore the feasibility of inkjet deposition for colloids, a novel drop-on-demand fluid dispenser is constructed to eject various types of liquids to produce atomized droplets. To make structured nanomaterials on a substrate using inkjet techniques, it is essential to determine the dynamical properties of the droplets as they are being formed. These would include the ejection speed, acceleration, terminal velocity and flight trajectories. For measuring these dynamic parameters, we successfully dispensed propylene glycol solution in different mixing ratios. This forms a reference fluid for establishing a baseline for our investigations. Our experimental data suggest that rapidly ejected droplets can be accurately modeled using Newton's equations and Stokes' law. In this conference, we describe our experiments consisting of an innovative inkjet dispensing apparatus in synchronization with a high-resolution camera imaging system. Furthermore, we plan to discuss our research efforts in dispensing microdroplets for relevant materials, such as chemical colloidal suspensions containing nanoparticles and polymer based fluids. [Preview Abstract] |
Monday, March 3, 2014 2:03PM - 2:15PM |
B20.00015: Structural disorder and anomalous water diffusion in random packing of spheres Andrea Gabrielli, Silvia Capuani, Marco Palombo, Vito D.P. Servedio, Giancarlo Ruocco Nowadays Nuclear Magnetic Resonance diffusion (dNMR) measurements of water molecules in heterogeneous systems have broad applications in material science, biophysics and medicine. Up to now, microstructural rearrangement in media has been experimentally investigated by studying the diffusion coefficient ($D(t))$ behavior in the tortuosity limit. However, this method is not able to describe structural disorder and transitions in complex systems. In this talk we show that, according to the continuous time random walk framework, the dNMR measurable parameter $\alpha $, quantifying the anomalous regime of $D(t)$, provides a quantitative characterization of structural disorder and structural transition in heterogeneous systems. This is demonstrated by comparing $\alpha $ measurements obtained in random packed monodisperse micro-spheres with Molecular Dynamics simulations of disordered porous media and 3D Monte Carlo simulation of particles diffusion in these kind of systems. Experimental results agree well with simulations that correlate the most used parameters and functions characterizing the disorder in porous media [1]. \\[4pt] [1] M. Palombo, A. Gabrielli, V.D.P. Servedio, G. Ruocco, S. Capuani, Scientific Reports \textbf{3}, 2631 (2013), doi:10.1038/srep02631 [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700