Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session G27: Focus Sessions: The Physics of Electrospray and Electrospinning: Current Knowledge and State of the Art IIElectro
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Chair: Alexander Yarin, University of Illinois Chicago Room: 709 |
Monday, November 20, 2017 10:35AM - 10:48AM |
G27.00001: Highly Transparent and Conductive Metallized Nanofibers by Electrospinning and Electroplating Sam S. Yoon, Alexander L Yarin Transparent conducting films (TCFs) and transparent heaters (THs) are of interest for a wide variety of applications, from displays to window defrosters. Here, we demonstrate production of highly flexible, conducting, and transparent copper (Cu), nickel (Ni), platinum (Pt), and silver (Ag) nanofibers suitable for use not only in TCFs and THs but also in some other engineering applications. The merging of fibers at their intersections (i.e. self-junctioning) minimizes contact resistance in these films. These metallized nanofibers exhibited a remarkably low sheet resistance at a high optical transmittance. This low sheet resistance allows them to serve as low-voltage heaters, achieving a high heating temperature at a relatively low applied voltage. These nanofibers are free-standing, flexible, stretchable, and their mechanical reliability was confirmed through various mechanical endurance tests. [Preview Abstract] |
Monday, November 20, 2017 10:48AM - 11:01AM |
G27.00002: Faradaic Reaction Mechanisms in Leaky Dielectric Liquids (Oils) Abhilash Sankaran, Christopher Staszel, Farzad Mashayek, Alexander Yarin Leaky dielectric liquids constitute a class of conductors capable of being electrified to possess a net charge. Faradaic reactions have been recently demonstrated to be responsible for the electrification of such liquids as oils in electrostatic atomizers. Here we address questions related to fundamental chemical kinetics and physical mechanisms and experimentally demonstrate the applicability of the Frumkin-Butler-Volmer kinetic model. We also introduce a novel method of measurement of the electric conductivity of oils. The role of the fatty acids in faradaic reactions is studied, as well the effect of the surrounding humidity on the physico-chemical mechanisms responsible for the ionic conductivity of oils. Cathodic and anodic reactions are discussed in detail, as well as the visible deposits formed at electrode surfaces. [Preview Abstract] |
Monday, November 20, 2017 11:01AM - 11:14AM |
G27.00003: A numerical study on charging mechanism in leaky dielectric liquids inside the electrostatic atomizers Babak Kashir, Anthony Perri, Alexander L. Yarin, Farzad Mashayek The charging of leaky dielectric liquids inside an electrostatic atomizer is studied numerically by developed codes based on OpenFOAM platform. Faradaic reactions are taken into account as the electrification mechanism. The impact of ionic finite size (steric terms) in high voltages is also investigated. The fundamental electrohydrodynamic understanding of the charging mechanism is aimed in the present work where the creation of polarized near-electrode layer and the movement of charges due to hydrodynamic flow are studied in conjunction with the solution of the Navier-Stokes equations. The case of a micro channel electrohydrodynamic flow subjected to two electrodes of the opposite polarity is considered as an example, with the goal to predict the resulting net charge at the exit. Even though the electrodes constitute a small portion of the channel wall, otherwise insulated, it is indicated that the channel length plays a dominant role in the discharging net charge. The ionic fluxes at the electrode surfaces are accounted through the Frumkin-Butler-Volmer relation found from the concurrent in-house experimental investigations. [Preview Abstract] |
Monday, November 20, 2017 11:14AM - 11:27AM |
G27.00004: Molecular modeling of field-driven ion emission from ionic liquids Fei Zhang, Yadong He, Rui Qiao Traditionally, operating electrosprays in the purely ionic mode is challenging, but recent experiments confirmed that such operation can be achieved using room-temperature ionic liquids as working electrolytes. Such electrosprays have shown promise in applications including chemical analysis, nanomanufacturing, and space propulsion. The mechanistic and quantitative understanding of such electrosprays at the molecular level, however, remain limited at present. In this work, we simulated ion emission from EMIM-PF6 ionic liquid films using the molecular dynamics method. We show that, when the surface electric field is smaller than $\sim $1.5V/nm, the ion emission current predicted using coarse-grained ionic liquid model observes the classical scaling law by J. V. Iribarne and B. A. Thomson, i.e., ln(Je/$\sigma )\sim $En$^{\mathrm{1/2}}$. These simulations, however, cannot capture the co-emission of cations and anions from ionic liquid surface observed in some experiments. Such co-emission was successfully captured when united-atom models were adopted for the ionic liquids. By examining the co-emission events with picosecond, sub-angstrom resolution, we clarified the origins of the co-emission phenomenon and delineate the molecular events leading to ion emission. [Preview Abstract] |
Monday, November 20, 2017 11:27AM - 11:40AM |
G27.00005: ABSTRACT WITHDRAWN |
Monday, November 20, 2017 11:40AM - 11:53AM |
G27.00006: Computational and Experimental Studies of Electrospray Deposition of Nanoparticle Suspensions Xin Yong, Ao Li, Nicholas Brown, Mingfei Zhao, Yaqun Zhu, Guy German, Paul Chiarot Electrospray offers unique capabilities for deploying colloidal suspensions to create nanoparticle films and coatings. It can deliver precise quantities of particles in a dry state and overcomes many limitations of other technologies. We integrate simulations and experiments to elucidate the relationship between the key operating parameters and the structure of an electrospray deposit. We investigate the role of the electrospray time, the target substrate properties, and the polydispersity of the colloidal suspensions. The deposition patterns are similar for all spray times and substrates. In particular, the deposited particles segregate to the center and edge of a deposit, leaving a depletion region in between. Using a Lagrangian particle tracking method with convective droplet evaporation, we highlight the critical role of the space charge interactions inside the plume in governing the trajectory of the emitted particles and the ensuing deposit morphology. The microstructure of a deposit is also influenced by the electrical conductivity of the target substrate. The residual charges on the particles deposited on to a dielectric substrate influence the deposition of subsequent in-flight particles. [Preview Abstract] |
Monday, November 20, 2017 11:53AM - 12:06PM |
G27.00007: The influence of electrostatic forces on the deposition of particles from a volatile carrier liquid Ofer Manor, Anna Zigelman Electrostatic forces are known to influence the pattern deposition of colloidal particles on a solid substrate. Several experimental studies suggest a direct connection between the morphology of the deposits and the electrical potential on the particles in the carrier liquid and on the substrate. The path by which electrostatic forces may influence the deposition was attributed to the adsorption of particles to the substrate and the coagulation of particles in the liquid. Here, we use theory to test this assertion. We employ the interaction--force boundary layer theorem and the Smoluchowski theorem to determine the rate of adsorption and coagulation, respectively, from the free energy in the system. The expressions for coagulation and adsorption are added to a dynamic advection-diffusion equation, which governs the transport of particles in the liquid. We thus present a continuum formulation for the influence of electrostatic forces on the adsorption and coagulation of particles in a volatile liquid drop. It appears that one should expect to find larger aggregates of particles near the edge of the drop when coagulation takes place. In addition, fast particle adhesion to the solid substrate will smear the morphology of the deposits. Sufficiently fast adhesion will lead to the formation of dome or disk shaped deposits. [Preview Abstract] |
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