Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Y8: Hydrodynamics of Surfaces and Films |
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Sponsoring Units: DFD Chair: Elizabeth Mann, Kent State University Room: Morial Convention Center RO6 |
Friday, March 14, 2008 11:15AM - 11:27AM |
Y8.00001: Capillary ratchet: Hydrodynamics of capillary feeding in shorebirds Manu Prakash, David Quere, John Bush Bill morphologies are highly specialized to particular foraging strategies in birds, as is apparent from the large diversity of beak shapes observed in nature. Here we present an experimental and analytical study of capillary feeding in shorebirds. We highlight the critical role of contact angle hysteresis in capillary feeding. Our study provides a simple physical rationalization for the observation of multiple mandibular spreading cycles in feeding, necessary to overcome contact line resistance. We also find a unique geometrical optima in beak opening and closing angles for the most efficient drop transport. This capillary ratchet mechanism may also find applications in micro scale fluid transport, such as valveless pumping of fluid drops. [Preview Abstract] |
Friday, March 14, 2008 11:27AM - 11:39AM |
Y8.00002: Rheology and Microrheology of Actin-Lipid Composites at the Air-Water Interface Robert Walder, Alex Levine, Christoph Schmidt, Michael Dennin We report on the mechanical properties of a composite material that is a combination of a Langmuir monolayer chemically linked to an actin filament network. This composite system is a 2 dimensional analogue of a cellular membrane and is also expected to have interesting nonlinear mechanical properties. To measure these mechanical properties, we employ traditional rheology and have developed unique microrheological capabilities based on an optical tweezer setup combined with a Couette surface rheometer. This combination of techniques will allow the study of both bulk and local mechanical responses of the composite material to external forces. Studying such materials allows us to simultaneously study a biomimetic material that should provide useful insights into the mechanical properties of biological cells, while also providing a 2 dimensional soft matter system to study the properties of semi-flexible polymer networks. [Preview Abstract] |
Friday, March 14, 2008 11:39AM - 11:51AM |
Y8.00003: ABSTRACT WITHDRAWN |
Friday, March 14, 2008 11:51AM - 12:03PM |
Y8.00004: Elasticity and capillarity: wet hairs and origami Jos\'e Bico, Lingguo Du, Benoit Roman, Jerome Guilet Capillary forces are responsible for a large range of everyday observations : the shape of rain droplets, the imbibition of a sponge, the clumping of wet hair into bundles. Although they are often negligible on macroscopic structures, surface capillary forces may overcome volume forces at small scales and deform compliant micro-structures. Capillary-induced sticking can prevent the actuation of mobile elements in MEMS, or even cause their collapse. Capillary forces also have important consequences in biology such as the buckling of the airway lumen induced by surface tension, which can eventually cause the lethal closure of lung airways. We will review a few experimental situations where capillary forces are able to deform two types of objects: rods, and thin sheets. For instance, the nanotubes of a ``carbon nanotube carpet'' self-assemble into conical ``teepee'' structures after the evaporation of a solvent and can produce intriguing cellular patterns. Similarly macroscopic wet hairs tend to assemble into bundles through a cascade of successive pairings. The comparison of the physical ingredients involved in these phenomena, attracting capillary forces acting against bending elasticity, leads to a characteristic length: a slander structure longer than this ``elasto-capillary'' length is considerably bent by capillary forces. The case of thin sheets is trickier because of geometrical constrains, which generally leads to singularities. [Preview Abstract] |
Friday, March 14, 2008 12:03PM - 12:15PM |
Y8.00005: Flow fields in soap films: effects of surface viscosity and film thickness Vikram Prasad, Eric R. Weeks A soap film is a thin fluid layer (10 nm to 10 microns thick) separated from bulk air phases above and below it by two surfactant monolayers. We measure the flow field in these films by two-particle microrheology, which looks at the correlated Brownian motion of pairs of embedded tracer particles separated by a distance R. In thin soap films with the thickness comparable to the particle size, and with mobile surfactant interfacial layers, this flow field is long ranged. On the other hand, the flow field in a 3D fluid is known to decay as 1/R. We vary the thickness of the soap film, the mobility (surface viscosity) of the interface and the size of the polystyrene probe particles to quantify the transition of the hydrodynamics of the film from quasi-2D to 3D-like behavior. [Preview Abstract] |
Friday, March 14, 2008 12:15PM - 12:27PM |
Y8.00006: Effective Viscosity of a Dilute Suspension of Membrane-bound Inclusions Mark L. Henle, Alex J. Levine In 1906, Einstein famously calculated the effective viscosity of a dilute solution of spheres suspended in a viscous solvent [\textit{Annalen der Physik} \textbf{19}, 289 (1906)]. In this talk, we consider the two-dimensional analogue of~this problem: that is, we calculate the effective viscosity of a dilute suspension of disks embedded in a two-dimensional fluid membrane. The rheological properties of particle-decorated membranes and fluid-fluid interfaces are important in a variety of soft matter systems. ~For example, the cell membrane contains a suspension of membrane-bound inclusions (e.g. transmembrane proteins, lipid rafts), which modifies the transport kinetics of the membrane. Also, the interfacial viscosity of liquid-liquid interfaces in colloid-stabilized emulsions plays a key role in preventing droplet coalescence. We include the dissipation caused by flows both within the membrane and in the surrounding bulk fluids. When the flows within the membrane dominate the dissipation, the particle suspension effectively shifts the membrane viscosity. Conversely, when flows induced in the bulk fluids dominate the dissipation, the suspension in the membrane shifts the bulk viscosity. In both limits, we obtain simple analytic expressions for the appropriate effective viscosity. [Preview Abstract] |
Friday, March 14, 2008 12:27PM - 12:39PM |
Y8.00007: Contact line motions of drying solutions Francois Lequeux, Cecile Monteux, Astrid Tay, Emmanuelle Rio, Laurent Limat, Guillaume Berteloot, Adrien Daerr If most the studies on wetting deal with pure liquids in the absence of evaporation, in practical situations, the liquid is often a solution with an evaporating solvent. This is encountered both in coating and in surface cleaning. In that case, the contact line of a solution is the location of many divergent phenomena. The hydrodynamics dissipation diverges at the contact line: 1) the drying rate diverges at the contact line 2) the concentration diverges at the contact line. The coupling of these phenomena leads to complex effect for the contact line motion. We have observed that an advancing contact line of a colloidal suspension exhibit a stick-slip motion. Moreover, for similar reasons in the case, an advancing contact line of a polymer solution, the contact angle exhibit a minimum as a function of velocity -- at which the polymer accumulates on a length of typically 5 nm in the vicinity of the contact line. All these phenomena can explained quantitatively using simple scaling arguments that we will present. [Preview Abstract] |
Friday, March 14, 2008 12:39PM - 12:51PM |
Y8.00008: Obtaining Reproducible Slip Measurements on Smooth Hydrophobic Surfaces Sean P. McBride, B.M. Law Over the past decade, the world market for microfluidic technologies and applications of such devices has soared. The slip length parameter at the liquid-surface interface of these devices describes how easily a fluid flows over the surface. As microfluidic devices decrease in size, slip becomes very important. Despite the undeniable success of these devices in recent years, the literature illustrates that numerous discrepancies exist for the slip magnitude measured using different experimental methods. As the need for smaller microfluidic devices approaches a consistent experimental method is needed to obtain reproducible slip results. The method employed to study slip, in this research, uses an Atomic Force Microscope (AFM) to obtain the hydrodynamic force exerted on a colloidal cantilever which is immersed in a homologous series of test liquids and driven toward a smooth hydrophobic surface. The surfaces are prepared using silicon wafers with 0.4nm RMS over a 5x5um area and coated with hexadecyltricholorsilane (HTS) via cold liquid deposition. This method provides reliable and reproducible slip measurements that are consistent with a constant slip length over a wide shear rate range. This research was supported by NSF grant DMR-0603144. [Preview Abstract] |
Friday, March 14, 2008 12:51PM - 1:03PM |
Y8.00009: Fabrication of non-aging superhydrophobic surfaces by packing flower-like hematite particles Anmin Cao, Liangliang Cao, Di Gao We demonstrate the fabrication of non-aging superhydrophobic surfaces by packing flower-like micrometer-sized hematite particles. Although hematite is intrinsically hydrophilic, the nanometer-sized protrusions on the particles form textures with overhanging structures that prevent water from entering into the textures and induce a macroscopic superhydrophobic phenomenon. These superhydrophobic surfaces do not age even in extremely oxidative environments---they retain the superhydrophobicity after being stored in ambient laboratory air for 4 months, heated to 800 degree C in air for 10 hours, and exposed to ultraviolet ozone for 10 hours. [Preview Abstract] |
Friday, March 14, 2008 1:03PM - 1:15PM |
Y8.00010: Liquid slip probed by second harmonic generation Dan Lis, Steve Granick, Bae Sung Chul Second harmonic generation has been used to probe how a solid surface responds to flow past it. The surface is quartz, the measurements are made in total internal reflection configuration, and comparison of responses to light with s and p incident polarisation allows us to determine the orientation of dye molecules physisorbed before the onset of the shear flow. By monitoring the orientation of the dye at different fluid viscosity and different shear rate, we deduce the surprising relation between shear rate and surface stress. [Preview Abstract] |
Friday, March 14, 2008 1:15PM - 1:27PM |
Y8.00011: Determination of Inter-Phase Line Tension in Langmuir Films Elizabeth K. Mann, Lu Zou, Jacob R. Wintersmith, Andrew J. Bernoff, James C. Alexander, J. Adin Mann, Jr., Prem Basnet, Edgar E. Kooijman The hydrodynamic response of a thin fluid film, whether a Langmuir monolayer at the air/water interface or a cell membrane, is difficult to model, since it involves the coupling of both bulk and surfaces phases. However, such hydrodynamic response is not only intrinsically critical for transport within the layer, it also provides the major available means to evaluate an important parameter for phase-separated layers, the line tension. We have developed a line-integral formulation of the hydrodynamic response of phase-separated layers with short-ranged forces, and tested it by comparisons between numerical simulations based on this model and experiment. These experiments both validate the model and demonstrate that the line tension can be determined with unprecedented accuracy and precision. Two systems have been studied to date: a simple smectic liquid crystal multilayer and coexistence between phases in binary lipid/cholesterol mixed layers. For the latter case, long-range dipole-dipole interactions are introduced into the model. [Preview Abstract] |
Friday, March 14, 2008 1:27PM - 1:39PM |
Y8.00012: ABSTRACT WITHDRAWN |
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