Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E19: Thin Films |
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Chair: Randy Ewoldt, University of Illinois at Urbana-Champaign Room: 28E |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E19.00001: Interaction model between a liquid film and a spherical probe Rene Ledesma Alonso, Dominique Legendre, Philippe Tordjeman To find a liquid surface profile, when performing AFM measurements, probe interaction effects should be identified. Herein, the behavior of a liquid film free surface (thickness $E$, surface tension $\gamma$ and density difference $\Delta \rho$), disposed over a flat surface and in the presence of a spherical probe (radius $R$) is forecast. A bump-like surface shape is observed, due to the probe/film interaction (characterized by the Hamaker constant $H_{pl}$). In addition, the attraction between the film and the substrate (depicted by $H_{sl}$) opposes the axial and radial deformation ranges. Several parameters portray the equilibrium shape: Bond $B_o=(\Delta\rho gR^2)/\gamma$ and modified Hamaker $H_a=4H_{pl}/(3\pi\gamma R^2)$ numbers, Hamaker ratio $A=H_{ls}/H_{pl}$, separation distance $D/R$ and film thickness $E/R$. We focus on the effect of geometry, nevertheless special attention is given to the role of physical parameters. Employing an augmented Young-Laplace equation, the equilibrium profile is described by a strongly non-linear ODE. A critical distance, below which the irreversible wetting process of the spherical probe occurs, is predicted. Our results provide simple relationships between parameters, which determine the optimal scanning conditions over liquid films. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E19.00002: Dynamics of precursor films Mark Franken, Christian Poelma, Jerry Westerweel The precursor film, formed ahead of a macroscopic droplet edge during spreading, is studied experimentally using a technique based on Total Internal Reflection Fluorescence Microscopy. This microscopy technique uses an evanescent wave resulting from total internal reflection of incident light to illuminate a fluorescent dye. The technique has sufficient spatial as well as temporal resolution, allowing us to measure the precursor film for different contact line velocities and liquids. We find that the precursor film thickness h(x) scales as 1/sqrt(x) and is independent of contact line velocity (hence capillary number). These results confirm for the very first time the theoretical predictions based on slip at the solid surface. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E19.00003: Lubrication analysis of the nanometric coating film deposited during gravure printing Umut Ceyhan, Rungrot Kitsomboonloha, S.J.S. Morris, Vivek Subramanian We report the importance of doctor blade-tip's geometry and wettability on the formation of coating film of thickness 1-10 nm after wiping of the excess ink used for gravure printing of electronics. Several authors have worked on the blade coating problem, addressing elastohydrodynamic effects; however, the coating film deposited during gravure printing is about 3 orders of magnitude thinner than micrometer scale created in blade coating. The blade-tip radius is consequently large compared with the film and gap thickness, allowing the blade tip to be approximated by a parabola. Hydrodynamic forces are concentrated within this inner region. In the gap entry, streamlines converge making the pressure large and positive; downstream, streamlines diverge making pressure large, but negative. This large negative pressure affects the coating film thickness by tending to draw the meniscus back into the narrow gap. Gap thickness and coating film thickness are determined as part of the solution of a free-boundary problem: we couple lubrication analysis of the gap flow in the gap to Landau-Levich analysis of the film flow. The resultant hydrodynamic force and couple exerted within the inner region are compared with those exerted on the outer portion of the blade and parameters affecting the solution of the problem on the coating film formation are examined in detail. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E19.00004: Experimental study of the residue film in direct gravure printing of electronics Rungrot Kitsomboonloha, Umut Ceyhan, S.J.S. Morris, Vivek Subramanian Direct gravure printing is a promising candidate for high resolution printing of electronics. During gravure printing, excess ink is removed from a patterned plate by a doctor blade and a residue film $\sim $10nm thick is left on the non-patterned area. This residue film degrades the pattern fidelity and has to be minimized. To understand the issues involved, we performed experiments on this residue film using a custom printer. We investigated the effects of wettability, ink viscosity and printing speed to understand the mechanisms of residue film formation. The results reveal that there are two types of residue film, originating from the wettability of the printing components and elastohydrodynamics. The first is a cell-dependent residue film, produced by the doctor blade dragging ink out from engraved cells. The second is a uniform residue film, which is caused by an increase in the gap between the patterned plate and doctor blade due to elastohydrodynamic pressure. As the capillary number increases, the cell-dependent residue film decreases, while the uniform residue film increases. These two types of residue films force gravure printing to be operated within a regime covering carefully controlled wettability, ink viscosity and printing speed, where the residue film is minimized. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E19.00005: Nanometer-scale free surface flow of molten polyethylene from a heated atomic force microscope tip Randy Ewoldt, Jonathan Felts, Suhas Somnath, William King We experimentally investigate nanometer-scale free surface flow of molten polyethylene from a heated atomic force microscope (AFM) cantilever, a nanofabrication process known as thermal dip-pen nanolithography (tDPN). Fluid is deposited from the AFM tip onto non-porous substrates whether the tip is moving or fixed. We find that polymer flow depends on surface capillary forces and not on shear between tip and substrate. The polymer mass flow rate is sensitive to the temperature-dependent polymer viscosity. Additionally, the flow rate increases when a temperature gradient exists between the tip and substrate. We hypothesize that the polymer flow is governed by thermal Marangoni forces and non-equilibrium wetting dynamics caused by a solidification front within the feature. [Preview Abstract] |
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