Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B11: Thin Films Surface Flows and Interfaces IIRecordings Available

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Sponsoring Units: DFD Chair: Ton Gao, Michigan State University Room: McCormick Place W181B 
Monday, March 14, 2022 11:30AM  11:42AM 
B11.00001: Wetting Dynamics in a Rectangular Channel Jiajia Zhou, Chen Zhao, Tian Yu, Masao Doi We analyze the dynamics of liquid filling in a thin, slightly inflated rectangular channel driven by capillary forces. We show that although the amount of liquid in the channel increases in time following the classical LucasWashburn law (t^{1/2} scaling), the prefactor is very sensitive to the deformation of the channel because the filling takes place by the growth of two parts, the bulk part (where the cross section is completely filled by the liquid), and the finger part (where the cross section is partially filled). We calculate the time evolution of bulk and finger accounting for the coupling between the two parts and show that the prefactor for the filling can be reduced significantly by a slight deformation of the rectangular channel, e.g., the prefactor is reduced 50% for a strain of 0.1%. This offers an explanation for the large deviation on the value of the prefactor reported previously. 
Monday, March 14, 2022 11:42AM  11:54AM 
B11.00002: Electrolytes in Confinement by Conductive Surfaces Felipe Jimenez, Monica Olvera De La Cruz Electrolytes in confinement near conductive surfaces are present in numerous applications including energy storage, sensors, and nanofluidic devices, thereby understanding electrostatic interactions near conductive interfaces is of prime importance. We investigate an electrolyte solution confined by two multilayered graphene surfaces. We discuss the effect of graphene being a conductor on the electrolyte structure, ionion interactions, and dielectric properties of the confined electrolyte. 
Monday, March 14, 2022 11:54AM  12:06PM 
B11.00003: Interfacial flow and thermodynamics of imidazoliumbased ionic liquids – oil lubricant Daria Lazarenko, Fardin Khabaz Ionic liquids (ILs) have enhanced tribological properties of lubricants when used as additives to conventional oils. In this work, we will use molecular dynamics simulations to study the dynamics and tribological properties of imidazoliumbased ILs in hexadecane (model oil) lubricant confined between two iron slabs. Our preliminary study shows that ions create layered structures near the metal surface. These layers show strong adhesion to the surface since the free energy of adsorption greatly exceeds kT. To efficiently design ILs with target interfacial properties, we will characterize the dynamics of ions and oil molecules by calculating the nonaffine meansquared displacement at different shear rates. The stress response and flow behavior of the liquid will be tracked to understand the slip mechanism at the metalIL and ILoil interfaces. Given that the stability of adsorbed layers depends on the orientation of molecules, we will quantify the local orientation along with the structure of ILs at these interfaces. This work will propose a model of ILbased additive to oils with controlled tribology as a more environmentally friendly solution for future lubricants. 
Monday, March 14, 2022 12:06PM  12:18PM 
B11.00004: Modeling thermal effects in the droplet assembly of nanoscale molten metal films Ryan H Allaire, Lou Kondic, Linda J Cummings The focus of this talk is the accurate modeling of thermal effects in nanoscale liquid metal films that are deposited on thermally conductive substrates, melted by an external heat source, and dewet into droplet patterns. Using asymptotic analysis we develop a novel model that accurately portrays heat conduction in the liquid film and such effects as temperature varying material parameters and phase changes. In particular, we analyze the effect the underlying substrate has on the evolution of the liquid film. By developing a 3D GPU code that solves the underlying partial differential equations we are able to simulate both film evolution and heat conduction on large domains. We find that many effects, such as temperature varying viscosity, strongly influence the dewetting mechanism of the film and, in many instances, leads to interesting frozen film patterns. 
Monday, March 14, 2022 12:18PM  12:30PM 
B11.00005: An Exact Analytic Solution for the Sakiadis Boundary Layer Cade C Reinberger We examine the classical problem of the Sakiadis Boundary Layer. Though a power series solution can be found, it has finiteand qualitatively smallradius of convergence, while the problem's domain is infinite. Barlow et al [Q. J. Mech. Appl. Math., 70 (1) (2017), pp. 2148] developed a solution combining an asymptotic series around infinity with the Taylor series via the method of asymptotic approximants. While this series solution was shown to converge over the physical domain, its representation as an exact solution to the ODE was not demonstrated. We demonstrate that the asymptotic series may be viewed as a Taylor series analytic on a disc larger than one containing the domain after suitable transformation of the relevant ODE. Furthermore, we provide explicit recursions that allow efficient computation of higherorder coefficients. We demonstrate that this exact expression converges uniformly, with the infinity norm of the error on the whole domain decreasing exponentially with the number of terms. Moreover, we verify the location of the singularity limiting the radius of convergence for the untransformed problem. We discuss conditions under which this methodology may be adapted to similar problems. 
Monday, March 14, 2022 12:30PM  12:42PM 
B11.00006: Hydrodynamics of a Multicomponent Vesicle Under Strong Confinement Ashley Gannon, Bryan Quaife, YuanNan Young, Shuwang Li The biophysical lipid bilayer membrane (such as a vesicle) often consists of multiple species of macromolecules such as cholesterol, surface proteins, surfactants, and different lipids. In this work I use the phasefield model for a multicomponent lipid membrane and implement the hydrodynamics with a boundary integral code. The simulations show that the multicomponent structure results in fundamentally different behaviors than a single component vesicle. I will demonstrate some of these differences by simulating multicomponent vesicles in various unbounded and strongly confined geometries. 
Monday, March 14, 2022 12:42PM  12:54PM 
B11.00007: Nanobubble capillary force between parallel plates Zhi Liang, Eric A Bird Molecular dynamics (MD) simulations are carried out to study the capillary force induced by a nanobubble (NB) capillary bridge between two parallel plates. While detection of the geometry of the capillary bridge in NB capillary force (NBCF) measuring experiments is currently very challenging, MD simulations can readily measure both the geometry of the NB capillary bridge and the resulting NBCF so that the correlation between the bridge geometry and the NBCF predicted by the capillary force model can be explicitly examined. Our modeling results show the simple capillary force model gives good prediction of the NBCF for both concave and convex NB capillary bridges. Furthermore, using the combination of the capillary force model and the ideal gas equation, we develop a theoretical model to predict the variation of the bridge geometry and the NBCF with the separation between two parallel solid surfaces. The continuum prediction of the NBCF shows the NBCF induced by a concave bridge remains attractive in the plate retraction process until the pinchoff of the bridge occurs, while the NBCF induced by a convex bridge exhibits a transition from repulsive to attractive in the plate retraction process. For convex bridges, there is an equilibrium separation between two solid surfaces where the NBCF is zero. The equilibrium separation depends on the contact angle and size of the capillary bridge. The continuum theoretical predictions are corroborated by the discrete MD simulation results and are consistent with the existing experimental data on NBCFs between two solid surfaces. 
Monday, March 14, 2022 12:54PM  1:06PM 
B11.00008: Sound and shear wave attenuation in confined fluids Hannes Holey, Peter Gumbsch, Lars Pastewka Lubricated friction is an inherent multiscale problem involving two surfaces under relative motion, separated by a viscous fluid. These surfaces typically have complex topography and chemistry, and together with the confined fluid, determine energy dissipation at the interface. We investigate sound and shear wave attenuation in confined fluids by means of both Molecular Dynamics (MD) and continuum simulations. For the latter, we show that the reduction of dimensionality in the lubrication equations leads to wavelengthindependent attenuation coefficients. Instead, wave attenuation is determined by the geometry of the gap and fluidwall interactions. This can lead to an underestimation of energy dissipation, when transferring continuum models to the molecular scale. On the other hand, MD simulations of confined fluids reveal a transition in their spectral attenuation behavior at characteristic wavelengths that are in the order of the gap height. In this talk, we will discuss the implications of this behavior for multiscale simulations of friction. 
Monday, March 14, 2022 1:06PM  1:18PM 
B11.00009: Experimental Investigation of a LowProfile Heat Pipe with Wickless WettabilityPatterned Condenser Mohamad Jafari Gukeh, George Damoulakis, Constatine M Megaridis Heat pipes (HP) are metalwick equipped cooling devices that circulate a phasechanging liquid to transfer heat over long distances more efficiently than solidmetal heat sinks. Metal wicks are commonly used in heat pipes, but also have capillary limits such as high pressure drop and poreclogging issues. Wettability patterned (WP) surfaces do not face these limitations and as shown here, could effectively substitute metal wicks in HPs. WP surfaces facilitate the collection and efficient transport of condensates, therefore enhancing heat transfer from the hot (evaporator) to the cold (condenser) side. In this study, a 10 cm long 5 mmthin HP with an axially graded wicklined evaporator and a wickless WP condenser is designed, fabricated, and tested. Condensation is controlled on the wickless side of the system via juxtaposed superhydrophilic/hydrophobic areas to regulate both dropwise and filmwise condensation, to collect and return the condensate to the evaporator's wick, thus increasing the maximum allowable heat load and lowering the device's thermal resistance (lowest 0.16 K/W at 105 W). Additionally, an axially graded wick improved condensate transport from the cold to the hot side of the system. Finally, the effect of wettability patterning and the wick’s pore size were examined 
Monday, March 14, 2022 1:18PM  1:30PM 
B11.00010: Omniphobic Surfaces for LowSurfaceTension Liquids Shashwata Moitra, George Damoulakis, Graham Kaufman, Craig Zuhlke, George Gogos, Constantine M Megaridis There has been substantial research on superhydrophobic (waterrepellent) surfaces, but only limited research on superoleophobic (oilrepellent) surfaces that can repel liquids with low surface tension. Water has a high surface tension 72 mN/m, which makes it simpler to repel, but when the fluid surface tension drops below 40 mN/m, repellency becomes more difficult. This situation is encountered in certain engineering applications and thus is of technological importance. In this work, we report a fluorinated nanocomposite coating deposited on a surface textured by femtosecond laser surface processing (FLSP), a scalable technique that requires no lithography implementation. The approach resulted in the repellency of liquids with surface tensions as low as 21 mN/m. The repellency of liquids with surface tensions from 72mN/m to 21mN/m is experimentally investigated. Comparisons are performed between the velocities acquired by fluids transported pumplessly on a wedgeshaped wettabilitypatterned track, due to confinement imposed by the superomniphobic background surrounding the superphilic track. Finally, transport length and velocities of lowsurface tension liquids transported on inclined ramps against gravity on similar wedgeshaped wettabilitypatterned tracks are being exhibited. 
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