Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q23: Invited Session: Dynamics of Fluids at Interfaces |
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Sponsoring Units: DFD DPOLY Chair: Joshua McGraw, Saarland University Room: 505-507 |
Wednesday, March 5, 2014 2:30PM - 3:06PM |
Q23.00001: Fluid transport at the nanoscale: application to osmotic energy harvesting Invited Speaker: Lyd\'eric Bocquet |
Wednesday, March 5, 2014 3:06PM - 3:42PM |
Q23.00002: Directed Assembly at Interfaces of Isotropic and Anisotropic Fluids Invited Speaker: Kathleen Stebe We exploit fields inherent to soft materials that contain colloidal particles to induce interactions and to direct particles to assemble into well-defined structures at given locations. The unifying concepts are that colloidal particles create deformations that store energy in soft matter, and that soft matter can be molded to create energy fields with which the particle sourced deformations can interact. Furthermore, since soft matter can be readily reconfigured, these approached pave the way to reconfigurable structures. Two examples are presented. In one, we exploit curvature fields at fluid interfaces to generate capillary interactions that steer particles along curvature gradients to given locations. Anisotropic particles adopt preferred orientations and migrate to sites of high curvature. The role of different aspects of the particle-sourced deformation and the imposed curvature field in driving these orientations and migrations is discussed. In the second example, we exploit elastic energies that arise in confined liquid crystals. By confining a nematic liquid crystal in a structure with well-defined anchoring conditions, the nematic director and its associated defect field can be molded to store elastic energy. This energy steers particles within the bulk or particles trapped at the nematic-air interface. We demonstrate this concept by creating defect rings around immersed microposts in a nematic liquid crystal. Particles trapped at the nematic air interface interact with this energy field, forming assemblies mimicking the defect texture. [Preview Abstract] |
Wednesday, March 5, 2014 3:42PM - 4:18PM |
Q23.00003: Coalescence of drops on a substrate Invited Speaker: Jacco Snoeijer When two drops come into contact they will rapidly merge and form a single drop. Here we address the coalescence of drops on a substrate -- an elementary process encountered for example during condensation and inkjet printing. We focus on the dynamics just after contact, by characterizing the growth of the thin bridge connecting the two drops. For very viscous drops we present similarity solutions for the bridge, and find that the bridge size grows linearly with time $t$. Both the dynamics and the self-similar bridge profiles are verified quantitatively by experiments. We then consider the coalescence of water drops, for which viscosity can be neglected and liquid inertia becomes rate-limiting for the merging process. Once again, we find that experiments display self-similarity, but now the bridge size grows with as $t^{2/3}$ or $t^{1/2}$, depending on whether the contact angle is above or below $90^\circ$. A geometry-based scaling theory is able to capture these observations. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:54PM |
Q23.00004: Correlation between surface topography and slippage Invited Speaker: Marcus Mueller Using Molecular Dynamics simulations of a polymer liquid flowing past flat and patterned surfaces, we investigate the influence of corrugation, wettability and pressure on slippage and friction at the solid-liquid interface. For one-dimensional, shallow, rectangular grooves, we observe a gradual crossover between the Wenzel state, where the liquid fills the grooves, and the Cassie state, where the corrugation supports the liquid and the grooves are filled with vapor. Using two independent flow set-ups, we characterize the near-surface flow by the slip length and the position, at which viscous and frictional stresses are balanced according to Navier's partial slip boundary condition. This hydrodynamic boundary position depends on the pressure inside the channel and may be located above the corrugated surface. In the Cassie state, we observe that the edges of the corrugation contribute to the friction. These simulation data illustrate the gradual crossover between the macroscopic behavior, where the friction is reduced in the Cassie state, and molecular scale corrugation, where the substrate roughness increases friction. [Preview Abstract] |
Wednesday, March 5, 2014 4:54PM - 5:30PM |
Q23.00005: Contact-line dynamics of colloidal interfaces Invited Speaker: Dirk Aarts The ongoing miniaturization in science and technology raises new questions about the behavior of liquids in confinement. One particularly suitable way to study strongly confined liquids is by combining colloid science with soft-lithography techniques. Here, we will focus on contact-line dynamics: as our model system we use a mixture of spherical colloids and non-adsorbing polymers, which allows us to directly study contact-line motion and the accompanying entrainment and pinch-off instabilities at the scale of the thermal interface fluctuations. We interpret our findings within a mesoscopic theoretical framework, where the small separation between fluid and system length scales can be matched to that of the experiments. It turns out that in this regime of length-scale overlap thermal fluctuations, wettability and gravity all play a crucial role in describing the dynamics. [Preview Abstract] |
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