Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K45: Thin Film Wetting and Solid-Liquid Interfaces |
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Sponsoring Units: DCMP Chair: Radu Cimpeanu, Oxford University-USE 4643 Room: BCEC 211 |
Wednesday, March 6, 2019 8:00AM - 8:12AM |
K45.00001: Morphological Evolution and Hysteresis in External Electric Field induced Instability in Viscoelastic Thin Films Sheetal Ranga, Rabibrata Mukherjee Self-organized instability patterns in thin films are of great interest in diverse scientific and technological applications. We investigated the surface instability in a viscoelastic film engendered by externally applied electric field perpendicular to the film surface in a capacitor geometry. Here the main destabilizing force is electrostatic pressure and the restoring effects arising out of stretching of the crosslinked elastomeric film. The external field polarizes the air-polymer interface and the film surface destabilizes itself to align in the direction of the applied field to minimize the energy forming different morphologies. We report here complete bonding-debonding sequence and morphological transformation. During bonding, the patterns appear only when the field strength (U) exceeds critical voltage (UC), which depends on the shear modulus, gap spacing, and film thickness etc. With an increase in U, initially columns appear which further evolves into labyrinths and holes before the film surface comes in complete conformal contact with the top electrode. During debonding, the patterns appear following exactly opposite morphological sequence. Though the patterns are completely switchable by electric field we have observed hysteresis during de-bonding. |
Wednesday, March 6, 2019 8:12AM - 8:24AM |
K45.00002: Transition from spin dewetted droplets to continuous film in a semi-crystalline Polyethylene Oxide thin film SOUMYAMOULI PAL, Rabibrata Mukherjee Polymeric thin films are increasingly being utilized for technological applications, such as coatings, functional surfaces, etc. Dewetting and crystallization both play a significant role in determining the film morphology and ultimate film properties. When polyethylene oxide (PEO) is spin coated from a nonpolar solvent (chloroform), crystallization proceeds via formation of spherulites, which correlate well with Avrami kinetics. Spontaneous rupture of the dispensed solution layer during spin coating results in isolated periodic morphologies of the solute at low concentrations (Cn). Here, the morphology of PEO thin films coated on pre-patterned PDMS substrate transforms from spin-dewetted droplets to elongated threads to continuous films with an increase in Cn. We investigated the effects of RPM variation during spin coating on the transition of spin-dewetted morphologies from droplets at lower RPM to continuous film at higher RPM. We further show that within the spin-dewetted regime, with a decrease in solute concentration and increase in RPM, droplet periodicity (λD) reduces and number density of droplets increases. Spherulite structures were observed in both spin-dewetted aligned droplets and continuous films; however, lamellar structures were observed in elongated threads. |
Wednesday, March 6, 2019 8:24AM - 8:36AM |
K45.00003: Influence of residual stress on dewetted morphology of spin coated polymer thin films ALOK PATRA, Anuja Das, Rabibrata Mukherjee Spontaneous instability in polymer thin film leading to its rupture and subsequent formation of polymer droplets is called Dewetting. In this regard, it is essential to investigate the fundamental properties of polymer leading to dewetting and its effect on the dewetted morphology. We report the dependence of dewetted morphology of polymer thin film on residual stress generated during spin coating. Unlike applied stress, residual stress arises due to polymer chain entanglement while the polymer is in solution state and endures high centripetal force. The spin-coated polymer film is at a metastable equilibrium state generating a residual stress among the polymer chains. We produce different residual stress in polymer thin film of same thickness by spin coating at different rotation speeds. Based on the degree of stress present, the dynamics of dewetting as well as morphology varies. From this we exhibit the contrast by dewetting the thin film by different techniques: Thermal annealing, solvent vapor and good solvent mediated dissolution. The contrast in the morphology is shown as a measure of droplet periodicity (λD) and diameter (DD). Consequently, we can qualitatively predict the degree of residual stress in thin film by its dewetted morphology without further characterization. |
Wednesday, March 6, 2019 8:36AM - 8:48AM |
K45.00004: Structure and dynamics of pseudo-partial wetting precursor films Emilie Verneuil, Francois Lequeux, Helene Montes, Claire Schune, Marc Yonger Wetting of liquids on high energy solids where the spreading parameter is positive is expected to lead to nanometer-thick precursor films spreading out of the macroscopic liquid body. In this film, Van der Waals interactions induce either disjoining or conjoining Derjaguin pressure that respectively tend to separate the film interfaces or to bring them together. |
Wednesday, March 6, 2019 8:48AM - 9:00AM |
K45.00005: Theoretical insights into the hydrophobicity of low index CeO2 surfaces Marco Fronzi, Hussein Assadi, Dorian Hanaor The hydrophobicity of CeO2 surfaces is examined here. Since wettability measurements are extremely sensitive to experimental conditions, we propose a general approach to obtain contact angles between water and ceria surfaces of specified orientations based on density functional calculations. In particular, we analysed the low index surfaces of this oxide to establish their interactions with water. and we found the CeO2 (111) surface to be the most hydrophobic, whereas the CeO2 (110) surface is mildly hydrophilic. Also, we found that the O terminated (100) surface was unstable unless fully covered by molecularly adsorbed water. We identified a strong attractive interaction between the hydrogen atoms in water molecules and surface oxygen, which gives rise to the hydrophilic behaviour of (110) surfaces. The findings here shed light on the origin of the intrinsic wettability of rare earth oxides in general and CeO2 surfaces in particular and also explain why CeO2 (100) surface properties are so critically dependant on applied synthesis methods. |
Wednesday, March 6, 2019 9:00AM - 9:12AM |
K45.00006: Inferring Boundary Viscosity Values from Shear Deformation of Molecularly Thin Films Kishan Makwana, Sandra Troian Derjaguin and co-workers in 1946 introduced a shear technique for inferring the boundary viscosity of ultrathin liquid films. Air blown through a slender horizontal slit is used to apply a constant shear stress to the free surface of an initially flat and uniform film. Newtonian films tend to distort streamwise into a wedge shape whose slope decreases in time. The viscosity of the film can then be extracted from the wedge slope. High resolution measurements of the deformed film shape are normally obtained by interferometry for microscale films or ellipsometry for molecular scale films. Over the years, it has become evident that liquid nanofilms can exhibit a shear response that deviates significantly from this ideal linear behavior. Various physical mechanisms have been proposed to help resolve discrepancies between theory and experiment. Here we present finite element simulations of the liquid deformation process to evaluate help assess the influences of different mechanisms. Based on quantitative comparison to experimental data, we describe which candidate mechanisms best fit the trends observed. |
Wednesday, March 6, 2019 9:12AM - 9:24AM |
K45.00007: Dependency of ice adhesion strength on surface wettability and roughness Marina Machado de Oliveira, Subash Kattel, Joseph Murphy, John Ackerman, William Rice, Vladimir Alvarado Ice adhesion mechanisms are poorly understood contributing to the limited effectiveness of current ice mitigation techniques.The ideal solution is to prevent ice accretion via suppression of ice adhesion on ice-phobic surfaces, which requires understanding ice-phobicity at a more fundamental level. Given the breadth of published results, we designed an experimental matrix to isolate the effects of roughness and dynamic water spreading on ice adhesion. To this end, we conducted detailed surface roughness maps and novel dynamic contact angle measurements on stainless steel, aluminum, and non-metallic materials. We varied temperature to evaluate a variety of conditions encountered in practice such as clear ice, mixed ice and rime ice. Dynamic hysteresis of the contact angle and adhesion are clear functions of the forcing frequency and amplitude as well as surface roughness in pendant drop experiments. These results are a step towards finding physics-based solutions to ice accretion challenges. |
Wednesday, March 6, 2019 9:24AM - 9:36AM |
K45.00008: Rapid Detection of Thalassaemia Carriers by Image Analysis of Dried Patterns of Blood and Plasma Droplets Manish Ayushman, Manikuntala Mukhopadhyay, Sunando DasGupta The drying of drops of biological fluids such as blood/plasma leads to the formation of several interesting and complex patterns. Specific diseases can give rise to distinct drying patterns where the final pattern will depend on a number of factors such as plasma content and the morphology of the red blood cells. Thalassaemia is the most common single gene disorder in which the production of haemoglobin is impaired. At present, the gold standard method, used for carrier detection in hospitals, requires expensive instruments, skilled manpower and significant time, making it difficult to be used as an on-site method. A rapid, portable and automated technology for thalassaemia carrier screening is hence of significant importance. The carrier samples were separated from the healthy ones based on their blood and plasma droplet drying patterns. Image analysis based tools were used to identify the distinct signatory features in the patterns of the respective samples and correlated to the results obtained from the gold standard method. The proposed technique can be instrumental in developing a rapid, less laborious and cost effective ‘on-field’ screening method thus enabling the initial screening of the carriers from the large population. |
Wednesday, March 6, 2019 9:36AM - 9:48AM |
K45.00009: Creeping of Salt Solutions: Influence of Surfactants Mohsin Qazi, Herish Salim, Etienne Jambon-Puillet, Daniel Bonn, Noushine Shahidzadeh Salt creeping, the growth of crystals from evaporating salt solutions beyond the solution boundary, is a very common and fascinating phenomenon. It has a significant impact in industrial processes involving high salt concentrations, for the sodification of agricultural soils and for the preservation of salt-contaminated buildings and artworks1. In spite of its importance, salt creeping remains poorly understood and there are consequently hardly or no measures to control the phenomenon2. We present new experiments using a custom-made setup, that allows to reproduce the creeping phenomenon in the laboratory and study the influence of environmental conditions and additives. We show that during evaporation of salt solutions, the creeping starts only when the contact angle reaches a well-defined critical value, allowing us to propose a mechanism for the creeping dynamics. In addition, a nucleation promoting surfactant promotes creeping whereas a nucleation inhibitor prevents it. |
Wednesday, March 6, 2019 9:48AM - 10:00AM |
K45.00010: Transient dynamics of viscous drop impact on immiscible liquid bath: A holistic analysis Kumari Trinavee, Sirshendu Misra, Naga Siva Kumar Gunda, Sushanta Mitra Droplet entry problems offer extensive opportunities to understand the non-trivial multifluid interaction and the resulting complex evolution of phase boundary. Although droplet entry problems on identical or miscible liquid pool has been prolifically studied, its immiscible counterpart is rather unexplored. In this work, we present our holistic approach coupling experimental observation with theoretical and numerical validation to better understand the dynamics of droplet impact for an oil droplet impinged on a water pool. Our focus is laid on understanding the topologically complex temporal evolution of the oil/water liquid interface. Images acquired from a high-speed camera has been processed to obtain the interface acceleration which in turn is used to calculate an assistive force field responsible for the pinch-off. An analysis involving the change in total energy in the penetration process for a flow field with negligible viscous dissipation has been presented. The experimental results are validated with a volume of fluid based numerical model developed in-house. Additionally, we investigated the equilibrium droplet shape beyond penetration and its dependence on the properties of surrounding fluid, which still is an unexplored area in literature. |
Wednesday, March 6, 2019 10:00AM - 10:12AM |
K45.00011: Investigation of the interaction between graphene membranes suspended and liquid by nano-infrared spectroscopy Leonel Meireles, Ingrid David Barcelos, Gustavo Arrighi Ferrari, Paulo Alexandre de Almeida Neves, Raul Oliveira Freitas, Rodrigo Gribel Lacerda The chemical properties of biological systems in their native living environment has been a constant ambition in life sciences. Infrared spectroscopy is a unique analytical tool that enables identification of chemical compounds by their natural molecular-vibrational signatures in a label-free mode. Here we report the development of a robust fluidic platform specifically designed for nanoscale resolved infrared spectroscopy of biomaterials in liquid environments. An advantage of our proposed fluidic chip is the use of an atomic-thin graphene layer as an optical window for accessing the liquid stream inside the micro-channels written in the silicon wafer. We demonstrate the feasibility of the platform for scattering scanning near-field optical microscopy for measuring the infrared fingerprint of typical biological fluids based on Dimethyl Sulfoxide, Phosphate, Citric Acid, and Human Serum Albumin. We foresee our development to serve as a template for future studies involving fundamental questions on the chemistry of in-solution nanoscale bio-systems. |
Wednesday, March 6, 2019 10:12AM - 10:24AM |
K45.00012: Underliquid wetting behavior of graphene: Is the hypothesis of wetting transparency valid? Sirshendu Misra, Naga Siva Kumar Gunda, Sushanta Mitra Since the inception of wetting transparency hypothesis, understanding the wetting behavior of graphene and its dependence on the choice of underlying support layer fostered significant attention from scientific community. However, wetting studies on submerged graphene coated substrates are relatively scarce despite promising practical applications (e.g. water harvesting, oil-water separation etc.). Here we attempt to understand the wetting characteristics of a monolayer of graphene coated on a glass substrate when submerged in a liquid bath. A wide range of droplet and surrounding liquid combinations have been investigated to assess the dependency on the interaction potentials. In general, partial transparency towards wetting is observed and the degree of the same is seen to demonstrate a non-trivial dependence on the polar and dispersive interaction potentials between the participating entities with the competition between wetting affinities of the droplet and the surrounding liquid with respect to the coated substrate displaying the most prominent effect. Taking cue from Trinavee et al. (Langmuir 2018, 34, 11695−11705), a modified theoretical model involving formation of an intermediate thin film is proposed to explicate this underliquid wetting phenomenon. |
Wednesday, March 6, 2019 10:24AM - 10:36AM |
K45.00013: Isotherm kinetics and rapid sorption activity of mesoporous vdW 2D sheets decorated with magnetic nanobeads Meenakshi Talukdar, Pritam Deb Two-dimensional (2D) van der Waals (vdW) adsorbent sheets represent as an emerging class of materials overcoming the limitations for oil adsorption. Here, the interaction between adsorbent and adsorbate can be realised by the adsorption isotherm of the adsorption process [\emph{Phys. Rev. Lett.} $\bf{120}$, 264502, 2018]. Besides, the kinetics of the adsorption process is an important characteristics in understanding the rate of adsorption mechanism in vdW sheets [\emph{Rev. Mod. Phys.} $\bf{89}$, 035005, 2017]. In addition to the standard isotherm and kinetics retention of the physical phenomena of the host magnetic nanocomposite system, our study has reported a promising adsorbent material for efficient and rapid oil recovery providing feasible solution towards the upcoming oil consumption [\emph{arXiv} $\bf{1806.03037}$, 2018]-[\emph{Indian Patent Application} $\bf{201831009592}$, 2018]. |
Wednesday, March 6, 2019 10:36AM - 10:48AM |
K45.00014: Effect of Catalysis-clustering on Gas-sensing Performance Nacir Tit, Muhammad Ali, Alaa Shaheen We present a theoretical investigation, based on a combined of density-functional theory (DFT) and non-equilibrium Green’s-functional (NEGF) formalism, to study the effect of catalysis-clustering on the sensor response. Specifically, the scope is to compare the adsorption and transport properties after chemisorption of CO2 molecules on iron (Fe) ad-atoms deposited on graphene nano-ribbons (GNR) in two different ways: (i) Five Fe ad-atoms deposited on GNR in scattered fashion; and (ii) A cluster of five Fe atoms deposited on GNR. The results of IV-curves calculations confirm stronger deviations in the case of scattered Fe ad-atoms and, consequently, stronger sensor response. This work suggests stronger sensitivity and selectivity to be reached by scattering ad-atoms of the transition-metal catalysis and with an optimization of their density. As the sensor response is based on the deviation of conductance from before to after the exposure to the gas, our results have indeed a direct application to fabricate solid-state based gas sensors working with high sensitivity at room temperature, to detect toxic and hazardous gases such as CO2. |
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