Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H28: Surface Tension Effects: General |
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Chair: Jonathan Boreyko, Virginia Tech University Room: 309 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H28.00001: Reducing Sliding Friction with Liquid-Impregnated Surfaces Mohammad Habibi, C. Patrick Collier, Jonathan Boreyko Liquid-impregnated surfaces are fabricated by infusing a lubricating liquid into the micro/nano roughness of a textured substrate, such that the surface is slippery for any deposited liquid immiscible with the lubricant. To date, liquid-impregnated surfaces have almost exclusively focused on repelling liquids by minimizing the contact angle hysteresis. Here, we demonstrate that liquid-impregnated surfaces are also capable of reducing sliding friction for solid objects. Ordered arrays of silicon micropillars were infused with lubricating liquids varying in viscosity by two orders of magnitude. Five test surfaces were used: two different micropillared surfaces with and without liquid infusion and a smooth, dry control surface. The static and kinetic coefficients of friction were measured using a polished aluminum cube as the sliding object. Compared to the smooth control surface, the sliding friction was reduced by at least a factor of two on the liquid-impregnated surfaces. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H28.00002: Differential approach to Capillary Breakup Rheometry: role of filament asymmetry induced by sample volume and strain Louise McCarroll, William Schultz, Michael Solomon We investigate the operating range of the 1-D, Newtonian, differential analysis for capillary breakup rheometry. Capillary breakup rheometry (CBR) derives specimen physical properties (e.g. viscosity) from measurements of the filament evolution after a sudden deformation. In our differential analysis, derivatives of the filament radius as a function of the axial coordinate and time are measured to determine the ratio of surface tension to viscosity. We evaluate the accuracy of the differential method by applying it to Newtonian fluids with a range of viscosities and for experiments with different sample volumes and strains. We investigate the impact of filament asymmetry on the performance of the differential method for the range of conditions studied and with a 1-D numerical model. This evaluation yields recommendations for using the differential CBR technique. We discuss the scope for extending the differential analysis to more complex cases, such as for insoluble surfactant at the fluid-air interface. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H28.00003: Stretching liquid bridges with moving contact lines: Comparison of model predictions and experiments Chung-Hsuan Huang, Marcio Carvalho, Satish Kumar Transfer of liquid from one surface to another plays a key role in printing processes. During liquid transfer, a liquid bridge is formed and then undergoes significant extensional motion while its contact lines are free to move on the bounding solid surfaces. In this work, we develop slender-jet and finite-element models of this phenomenon and compare the resulting predictions with experimental data. For very low capillary numbers (quasi-static stretching), predictions from both models agree well with the experimental data. For O(1) capillary numbers, the models predict that each surface receives half the liquid, in agreement with experimental observations. For intermediate values of the capillary number, predictions from each model can deviate substantially from each other and from the experimental data due to deviations between the predicted and the observed contact-line motion. The models are also used to understand the influence of initial bridge shape on liquid transfer and to rationalize experimental observations. The results from these fundamental studies will aid the optimization of gravure and other printing processes for manufacturing of printed electronic devices. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H28.00004: Wetting and phase separation in soft adhesion Katharine Jensen, Eric Dufresne In the classic theories of solid adhesion, surface energies drive deformation to increase contact area while bulk elasticity opposes it. However, recently solid surface tension has also been shown to play an important role in resisting deformation in soft materials. We explore the consequences for the physics of adhesive contact by performing experiments bringing small, rigid spheres into contact with compliant silicone gel substrates. We measure the quasi-static deformation of the substrate, particularly focusing on its structure near the contact line. In order to satisfy the wetting condition prescribed by surface tension balance while avoiding an elastic singularity at the contact line, we find that the gels undergo an adhesion-induced phase separation. This creates a four-phase contact zone with two additional, hidden contact lines. Our results indicate that accurate theories of adhesion of soft gels need to account both for the compressibility of the gel elastic network and for a non-zero surface stress between the gel and its solvent. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H28.00005: Cusps and cuspidal edges at fluid interfaces: existence and application Rouslan Krechetnikov One of the intriguing questions in fluid dynamics is on the interrelation between dynamic singularities in the solutions of fluid dynamic equations -- unboundedness of the velocity field in an appropriate norm -- and the geometric ones -- divergence of curvature at fluid interfaces. The present talk focuses on two generic interfacial singularities -- genuine cusps and cuspidal edges -- found here in both two and three dimensions thus establishing a relation between real fluid interfaces and geometric singularity theory. The key new finding is the necessary condition for the existence of geometric singularities, which is a variation of surface tension. It is also established here that the dynamic and geometric singularities entail each other only in the case of three-dimensional cusps. Explicit asymptotic solutions for the flow field and interface shape near steady-state singularities at fluid interfaces are developed as well. The practical motivation for the present study comes from the fundamental role interfacial singularities play in sustaining self-driven conversion of chemical into mechanical energy. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H28.00006: A control volume study of the pressure tensor across a liquid-vapour interface Carlos Braga, Petr Yatsyshin, Edward Smith, Andreas Nold, Benjamin Goddard, Nikos Savva, Markus Schmuck, Andrew Duncan, David Sibley, Serafim Kalliadasis The presence of an interface renders the properties of the system position dependent. The pressure tensor will no longer be uniform nor isotropic giving rise to the surface tension. The theory of Kirkwood-Buff gives a formal description of the surface tension based on the analysis of the local pressure tensor while capillary wave theory assumes the existence of an instantaneous intrinsic surface separating the liquid and vapour. Analysis of its Fourier components gives both structural and dynamical routes to compute the surface based on hydrodynamic theory. The defining equation of a capillary surface is given by the stress balance between the pressure tensors and the surface tension. Here, we employ the instantaneous interface as a representative surface across which we compute the local pressures following the seminal work of Irving and Kirkwood. The control volume approach to the Irving-Kirkwood expressions provides an exact balance between the stress and momentum transfer across the surface element allowing the study of the surface tension from a mechanical standpoint. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H28.00007: A flow map of Buoyancy-Marangoni convection in binary fluids driven by a horizontal temperature gradient Yaofa Li, Minami Yoda This talk discusses an experimental study of convection in a layer of volatile liquid subject to a horizontal temperature gradient, driven by thermocapillarity, solutocapillarity and buoyancy. We investigated a $\sim 0.3$~cm-deep layer of a methanol(MeOH)-water mixture in a sealed rectangular cuvette driven by a temperature difference $\Delta T \approx 6$~$^\circ$C for a range of pressures (and therefore different concentrations of air in the vapor space above the liquid $c_a$). Solutocapillarity was found to be strong enough to drive the liquid near the free surface towards the heated end over the entire horizontal 4.9~cm extent of the liquid layer when $c_a < 6$\% and the MeOH molar fraction $C_M > 20$\%, suggesting that binary-fluid coolants could reduce film dryout in two-phase thermal management devices. At lower $C_M$, the flow reverses near the heated end, however, suggesting that thermocapillarity is dominant at low (local) MeOH concentration. The maximum flow speed is found to be in reasonable agreement with that predicted by lubrication theory at low $c_a$. At $c_a> 80$\%, thermocapillarity drives the flow near the free surface away from the heated end. Finally, the flow becomes unsteady at intermediate values of $c_a$. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H28.00008: Thermo/Soluto-capillary instabilities in 3D bi-component liquid pools using DNS Adam Williams, Pedro Saenz, Prashant Valluri, Khellil Sefiane The behaviour of surface tension dominated flows in the presence of a temperature gradient and phase change is of great importance in designing micro-cooling devices. While evaporating pools and droplets have been investigated numerically and experimentally, these studies have dealt only with pure fluids. For bicomponent liquid mixtures, limited experimental studies have been conducted but a rigorous numerical model is absent. We present a two-phase multicomponent DNS model to simulate thermo/soluto-capillary instabilities in bicomponent liquid layers subject to a horizontal temperature gradient. The strategy fully accounts for a deformable interface using a variant of volume-of-fluid method. The presence of a second component introduces thermophoresis in the liquid phase which then gives rise to solutal Marangoni effects. By combining mixture thermodynamics with multiphase DNS, we investigate thermo/soluto-capillary and interfacial instabilities of a 3D bicomponent liquid pool. An important aspect we quantify is the strength of solutal over thermal Marangoni convection and its effect on stability of resultant interfacial waves and phase-separation in the liquid. The model is robust enough to include phase-change and the advection-diffusion of volatile species in the gas phase. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H28.00009: Tuning the Dynamics of Particles and Drops at Engineered Nanostructured Interfaces Carlos Colosqui, Antonio Checco Harnessing the full potential of current nanofabrication capabilities requires significant progress in understanding non-equilibrium phenomena produced by nanoscale interfacial structure and thermal motion. In diverse colloidal systems relevant to complex fluids and soft materials, the nanoscale interfacial structure can induce transitions from fast dynamics dominated by (deterministic) hydrodynamic and surface forces to arrested dynamics dominated by (random) thermally-activated processes. Recent work provides guidelines for engineering geometries and surface structures to tune the dynamic behavior of nano/microscale particles and droplets. For example, small reductions of the radius of a microparticle can lead to dramatic increases in the time for adsorption at liquid interfaces or membranes. Similarly, reducing the radius of a millimeter-sized droplet can lead to arrested spreading dynamics with logarithmic-in-time relaxation. Furthermore, nanostructured surfaces with directional asymmetry can convert thermal motion into directed transport processes at controllable rates. This talk will discuss theoretical and computational predictions that have been confirmed in recent experimental work by our and other groups and new predictions that can guide future experimental studies [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H28.00010: Antifreeze Polysaccharide Coating Study for De-icing Aircraft Katsuaki Morita, Hirotaka Sakaue, Azuma Ando, Yoshiyuki Matsuda, Hidehisa Kawahara Anti-icing or deicing of an aircraft is necessary for a safe flight operation. Mechanical processes, such as heating and deicer boot, are widely used. Deicing fluids, such as propyrene glycol and ethylene glycol, are used to coat the aircraft. However, these should be coated every time before the take-off, since the fluids come off from the aircraft while cruising. We study an antifreeze polysaccharide (AFPS) coating as a deicer for an aircraft. It is designed to coat on the aircraft without removal. Since an AFPS coating removes ice by reducing the interfacial energy, it would be an alternative way to prevent ice on the aircraft. We provide a temperature-controlled room, which can control its temperature under icing conditions (-8 and -4 $^{\circ}$C). Ice adhesion tests are performed for AFPS coating and compared with a fundamental specimen without the coating. [Preview Abstract] |
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