Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z43: Focus Session: Fluids Under Confinement, Instabilities |
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Sponsoring Units: DPOLY GSOFT Chair: Peter Yunker, Harvard University Room: 214C |
Friday, March 6, 2015 11:15AM - 11:27AM |
Z43.00001: Capillary Leveling of a Free-Standing Film Mark Ilton, Miles Couchman, Michael Benzaquen, Thomas Salez, Paul Fowler, Elie Rapha\"{e}l, Kari Dalnoki-Veress Capillary leveling has previously been used as a sensitive probe for nano-rheology in supported films. Using atomic force microscopy, we have observed the surface tension driven leveling of a step in viscous free-standing polystyrene films. We find that the step evolves to a self-similar profile with a width that scales with the square root of time. Film mobility is found to depend linearly on the film thickness. The scaling is fundamentally different from the capillary leveling observed in supported films (Poiseuille flow) because there is no shear of the fluid at the free surfaces (plug flow). The results agree with the lubrication approximation of Stokes equation with two shear-free boundaries. Free-standing capillary leveling provides a new tool to study glassy dynamics and molecular confinement in a free-standing geometry, as well as strong slip dynamics in the idealized limit of plug flow. [Preview Abstract] |
Friday, March 6, 2015 11:27AM - 11:39AM |
Z43.00002: Visualization of the Flow Field induced by an Oscillating Post in a 2D Fluid Membrane Z. Qi, K. Ferguson, J. Papaioannou, Y. Sechrest, T. Munsat, C.S. Park, M.A. Glaser, J.E. Maclennan, N.A. Clark, T. Kuriabova, T.R. Powers Thin fluid membranes immersed in a less viscous, bulk fluid are of fundamental interest as approximations of true two-dimensional (2D) fluids and as models of biological membranes. Many previous studies of such fluid membranes have focused on 2D macroscopic hydrodynamic effects such as the diffusion and interaction of inclusions, with fewer experimental investigations of microscopic properties such as the flow field. We have measured the 2D flow field generated by a rigid, oscillating post inserted in a freely suspended smectic liquid crystal film surrounded by air by analyzing the motion of tracer particles in the film. Our experiments confirm Saffman's prediction that the far-field flow velocity decays as 1/r (where r is the distance from the post) in the longitudinal direction, and as 1/r\textasciicircum 2 in the tangential direction. The measurements are in good agreement with flow fields computed using a model that generalizes the Levine/MacKintosh point-force response function. We have also investigated confinement effects that arise when the post is located near the film boundary. [Preview Abstract] |
Friday, March 6, 2015 11:39AM - 11:51AM |
Z43.00003: Time-harmonic Stokes Flow of a Newtonian Fluid in the Entrance Region of a Semi-infinite Circular Tube: Insights Involving the Estimation of Entrance Length and the Selection of Appropriate Entrance Boundary Conditions. Irwin S. Goldberg, Richard Lombardini Semi-analytic solutions to problems involving time-harmonic, axisymmetric Stokes flow in the entrance region of a semi-infinite, rigid, straight circular tube are examined. Double-transform methods are used to calculate sum-over-mode solutions for velocity components, velocity gradients, excess entry pressure, and vorticity. Various types of appropriate entrance conditions are identified in which combinations of pressure, velocity components, and/or velocity gradients are specified at the entrance boundary. The entrance length is estimated from the exponential spatial decay of the lowest normal-mode solution; the estimated entrance length is one-tube-radius for axisymmetric flow and two-tube-radii for non-axisymmetric flow. As a special case, the entrance length is shown to be equal to zero when boundary conditions are specified to have radially uniform pressure with the radial velocity component equal to zero at the entrance. Higher order, non-linear effects are discussed when low (non-zero) Reynolds numbers are involved; these effects include bidirectional streaming and the generation of higher harmonic oscillations. Both steady and time-harmonic flows are considered. [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:27PM |
Z43.00004: Effect of surface elasticity on the rheology of nanometric and micrometric liquids Invited Speaker: Elisabeth Charlaix The rheological properties of liquids confined to nanometer scales are important in many situations, yet are still a widely debated topic. The change in bulk viscosity and apparition of visco-elasticity under confinement is a particularly controversial question. In this talk, we use a new approach for this problem by addressing the effect of the long-range elastic deformations of the confining surfaces on the liquid flow. This effect could help reconciling some discrepancies within the literature concerning the intrinsic mechanical behavior of nanometric liquids. In the case of a squeeze-flow geometry, we show that below a critical distance Dc, the liquid is clamped by its viscosity and its intrinsic properties cannot be disentangled from the global system response. The theoretical approach [1] is confirmed by nanorheology experiments [2, 3] on various simple liquids, using both very soft (PDMS) and very rigid (Pyrex) confining surfaces. In every case we demonstrate that the elastic deflections of the confining surfaces, even if they are of very small amplitude, can dominate the overall mechanical response of nanometric liquids confined between solid walls. \\[4pt] [1] S. Leroy {\&} E. Charlaix, J. Fluid. Mech. 674, pp. 389-407 (2011)\\[0pt] [2] S. Leroy \textit{et al}., Phys. Rev. Lett. 108, 264501 (2012)\\[0pt] [3] R. Villey \textit{et al.,} Phys. Rev. Lett. 111, 215701 (2013). [Preview Abstract] |
Friday, March 6, 2015 12:27PM - 12:39PM |
Z43.00005: The Effect of Compression Frequency on the Collapse Dynamics of Langmuir Monolayers Jeremy Eaton, Michael Dennin We investigate the effects of compression speed and particle size on the collapse dynamics of an SDS-DODAB monolayer uniformly interspersed with fluorescent polystyrene nanoparticles ranging from 40 to 1000 nm in diameter. Folding and buckling are induced in the monolayer-particle system by compressing and expanding it between Teflon barriers which move at areal speeds ranging from 5 to 90 cm$^{\mathrm{2}}$/min. Video capture and fluorescence microscopy were used to image the monolayer over five compression-expansion cycles. Image processing is used to measure the surface particle density and is further used to characterize the number, structure and reversibility of the folds over time. These details provide insight on dynamics of monolayer collapse and will serve useful in determining the role folding plays in particle transport both within and across the monolayer interface. [Preview Abstract] |
Friday, March 6, 2015 12:39PM - 12:51PM |
Z43.00006: Plateau-Rayleigh Instability and Capillary Droplet Propulsion on a Fiber Sabrina Haefner, Michael Benzaquen, Oliver Baeumchen, Thomas Salez, Robert Peters, Joshua D. McGraw, Karin Jacobs, Elie Raphael, Kari Dalnoki-Veress The Plateau-Rayleigh instability (PRI) of a liquid column underlies a variety of hydrodynamic phenomena. Compared to the classical case of a free liquid column, the description of a liquid layer on a fiber requires the consideration of the solid-liquid interface in addition to the free surface. We revisit the PRI of a liquid layer on a solid fiber by varying the hydrodynamic boundary condition at the fiber-liquid interface from no-slip to slip. We find that the growth rate depends on the system geometry and the boundary condition, which is in agreement with theory. In the late stages of liquid column breakup on slip-fibers, a three-phase contact line can be formed on one side of the droplet. The resulting capillary imbalance leads to droplet propulsion, which is studied as a function of temperature and molecular weight. [Preview Abstract] |
Friday, March 6, 2015 12:51PM - 1:03PM |
Z43.00007: Parametric study of Newtonian droplet entering smaller confinement- a numerical study Zhifeng Zhang, Jie Xu, Xiaolin Chen Model of droplet entering a micro-confinement has wide applications in either design of microfilter or understanding of biological process such as Circulating Tumor Cell metastasis/ capillary blockage et al. In present numerical study, we explore the transient behavior of soft matter being squeezed through a micro-confinement by Newtonian droplet model. Parameter study quantify the relation between squeezing pressure under different channel/droplet size, channel geometry influence (circular, square, triangular) and flow velocity variance. [Preview Abstract] |
Friday, March 6, 2015 1:03PM - 1:15PM |
Z43.00008: Line tension and entropy in a liquid crystal Langmuir film Elizabeth Mann, Pritam Mandal, Joseph Yarzebinski, Nabin Thapa, J. Adin Mann Often two or more phases coexist within a monolayer or bilayer; the connection between these and possible dynamic or static microdomains within cell membranes is still debated. The line tension associated with the boundary between two phases within a monolayer or bilayer controls the size distribution, shape, and dynamics of domains. Theoretical models for this energy remain relatively untested. This work considers a model fluid system, trilayer/monolayer coexistence within a Langmuir film. The line tension associated with the boundary between these phases is measured as a function of temperature over a large range (12-37$^{\circ}$C). Compact, isolated trilayer domains are stretched from their equilibrium circular shape, and the free relaxation is analyzed with a hydrodynamic model previously tested by Wintersmith et al. [1] Line tension decreased with rising temperature. A careful treatment of the thermodynamics of the line boundary allow us to estimate the line entropy associated with the trilayer, and to test possible models for the boundary.\\[4pt] [1] Wintersmith, Jacob R.; Zou, Lu; Bernoff, Andrew J.; Mann, J. Adin Jr; Kooijman, Edgar E.; and Mann, Elizabeth K.. ``Determination of Interphase Line Tension in Langmuir Films.'' Physical Review E 75 (2007). [Preview Abstract] |
Friday, March 6, 2015 1:15PM - 1:27PM |
Z43.00009: Active nemato-hydrodynamics in toroidal microchannels Richard Green, John Toner, Vincenzo Vitelli We investigate flow driven by activity in nematic and polar fluids confined in a toroidal geometry. Using a perturbative expansion in the activity strength, we obtain closed form analytic solutions for the activity-driven flow. A distinguishing feature of this system is that there is no critical threshold which the activity needs to overcome in order to initiate the flow; rather, the flow is a consequence of the combination of activity and curved geometry at any non-zero activity, however small. [Preview Abstract] |
Friday, March 6, 2015 1:27PM - 1:39PM |
Z43.00010: Can a hard-sphere fluid feel the topology of a confining pore? Gerd Schroeder-Turk, Johannes Knauf, Roland Roth, Klaus Mecke The confinement of simple fluids to narrow pore spaces changes the phase behaviour. A central question is the dependence of thermodynamic properties on the pore shape $K$. The morphometric approach for simple fluids is derived by assuming that the grand potential $\omega(K,\mu,T)$ is an additive functional of $K$. Hadwiger's theorem states that $\omega(K,\mu,T)$ only depends on $K$ as a linear combination of the Minkowski functional, $\Omega=-p(\mu,T) V[K]+\sigma(\mu,T) A[K] + \kappa(\mu,T)C[K]+\overline{\kappa}(\mu,T)X(K)$ where $V$ and $A$ are the volume and interface and $C[K]$ the integrated mean curvature. $X[K]$ is the Euler number that characterises the pore topology. We use density functional theory to demonstrate that this theory is consistent, for the case of triply-periodic network-like pore geometries. For these, the formula $\langle N\rangle(K,\mu,T)=-\partial \Omega/\partial \mu$ can be inverted to give an estimate of $X_f$ deduced from the simulated densities -- the Euler number 'felt' by the fluid. We show that for the Primitive, Gyroid and Diamond minimal surfaces the obtained values are close to $X$. Counter-intuitively, this result suggests that hard sphere fluids can feel topological properties of a confining space, in addition to geometric ones. [Preview Abstract] |
Friday, March 6, 2015 1:39PM - 1:51PM |
Z43.00011: Controllable Coexistence of Multiple Instabilities on a Single Liquid Filament Michael Hein, Jean-Baptiste Fleury, Ralf Seemann Droplet based microfluidics exploits the decay of a liquid filament or cylinder into droplets of micrometric size. While the physics of droplet breakup on small scales remains a field of vivid interest, droplet based microfluidics has become widely used both in fundamental science and application such as (bio-)analytics or micro-chemistry. We present experimental research on the formation of droplets by breakup of a squeezed liquid filament surrounded by an immiscible phase that flows over a topographic step. This non-equilibrium process arises from the interplay between flow properties and interfacial instabilities when the filament is suddenly released from confinement at the step. In contrast to previous studies, a rich variety of different droplet breakup regimes was observed for the used geometry which are characterized by the coexistence of multiple liquid instabilities on a single filament. Surprisingly, these instabilities can be of different type while the filament is exposed to a symmetric flow-field. This spontaneous symmetry breaking is a nontrivial consequence of volume throughput constraints of each individual instability and allows for the specific production of heterogeneous droplet families from one single filament under constant flow rates. (Submitted 2014) [Preview Abstract] |
Friday, March 6, 2015 1:51PM - 2:03PM |
Z43.00012: Ginzburg-Landau and Weakly Nonlinear Analysis of 3D Pillar Growth in NanoBenard Instability Chengzhe Zhou, Sandra Troian We examine the nonlinear response of a molten nanofilm subject to strong interface deformation and patterned growth by destabilizing thermocapillary forces and stabilizing capillary forces. The equation for the moving boundary describes 3D growth induced by large thermocapillary stresses in the long wavelength approximation.\footnote{M.Dietzel and S. M. Troian, Phys. Rev. Lett. 103 (7), 074501(2009); M. Dietzel and S. M. Troian, J. Appl. Phys.108, 074308 (2010)} A bifurcation analysis via the method of multiple scales elucidates the influence of initial conditions, system geometry and material properties on the regimes describing stable and unstable flow. Investigation of the corresponding Ginzburg-Landau amplitude equation by finite element simulations reveals the existence of rich spatio-temporal phenomena. We will discuss how tightly ordered symmetric growth can arise from resonance effects induced by spatially periodic external forcing,\footnote{N. Liu and S. M. Troian, preprint (2014)} in analogy to behavior recently reported for the spatially forced version of the Swift- Hohenberg equation in 1- and 2- dimensions.\footnote{Y.Mau, L. Haim, A. Hagberg and E. Meron, Phys. Rev. E 88, 032917(2013)} [Preview Abstract] |
Friday, March 6, 2015 2:03PM - 2:15PM |
Z43.00013: Influence of Film Thickness and Substrate Geometry on the Growth of Taylor Cones in Perfectly Conducting Films Theodore Albertson, Sandra Troian Liquid metal ion and droplet sources are finding application in many different fields ranging from high resolution focused ion beam imaging and lithography to space micropropulsion to nanofabrication and nanomanufacturing. These applications require ever improved understanding of the process by which Maxwell forces deform a smooth molten metal film into a liquid cusp known as a Taylor cone. While recent computational studies have elucidated how the cone-jet transition controls the mass and charge flux, less attention has been paid to the regime involving very thin coating films and how frictional effects influence the shape and timescale of the evolving conical elongations. We describe recent efforts in our group using moving mesh techniques to quanify the influence of substrate geometry and film thickness on the shape and formation of transient Taylor cones in perfectly conducting films. Our results appear to confirm self-similar exponents predicted theoretically upon onset of cone formation. Under certain conditions, we find not only Taylor cone formation at the tip of a sharp axisymmetric emitter but also Taylor coronal rings away the sharpest point. Such secondary formations can ultimately enhance mass and charge flux. [Preview Abstract] |
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