Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X55: Surface and Interface Effects on Fluid and Particle Dynamics |
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Sponsoring Units: DPOLY DFD Chair: Adam Raegen, University of Waterloo Room: LACC 515A |
Friday, March 9, 2018 8:00AM - 8:12AM |
X55.00001: Beyond the Navier-de Gennes Paradigm: Slip Inhibition on Ideal Substrates Joshua McGraw, Mark Ilton, Thomas Salez, Paul Fowler, Marco Rivetti, Mohammed Aly, Michael Benzaquen, Elie Raphael, Kari Dalnoki-Veress, Oliver Baeumchen Hydrodynamic slip of a liquid at a solid surface represents a fundamental phenomenon in fluid dynamics that governs liquid transport at small scales. For polymeric liquids, de Gennes predicted that the Navier boundary condition together with the theory of polymer dynamics imply extraordinarily large interfacial slip for entangled polymer melts on ideal surfaces; this prediction was confirmed using dewetting experiments on ultra-smooth, low-energy substrates. Here, we use capillary leveling of polymeric films on these same substrates. Measurement of the slip length from a robust one-parameter fit to a lubrication model is achieved. At the lower shear rates involved in leveling experiments, these substrates can no longer be considered ideal. The data is consistent with physical adsorption of polymer chains at the solid/liquid interface. We extend the Navier-de Gennes description using one additional parameter, namely the density of physically adsorbed chains per unit surface. The resulting model is found to be in excellent agreement with the experimental observations. |
Friday, March 9, 2018 8:12AM - 8:24AM |
X55.00002: Capillary Levelling of a Liquid Stepped Film Supported on an Immiscible Liquid Film Carmen Lee, Vincent Bertin, John Niven, Thomas Salez, Elie Raphael, Kari Dalnoki-Veress Thin polymeric films have numerous technological applications and their stability has garnered intense interest. The stability and flow of a thin, viscous film is sensitive to the boundary conditions as the film thickness approaches the nanoscale. Here we probe a liquid-liquid boundary condition: a stepped polymer film is placed above a different, immiscible polymer film. The ensemble is supported by a solid substrate. The temporal evolution of the air-polymer interface, as well as the polymer-polymer interface were studied using atomic force microscopy. The polymer-polymer interface was exposed by using a selective solvent to remove the top film. Experimental results show that the step at the air-polymer interface levels off to minimize the excess surface area, and that there is substantial deformation at the interface between the two polymers during the levelling process. These experimental findings are discussed in the context of the lubrication model. |
Friday, March 9, 2018 8:24AM - 8:36AM |
X55.00003: The Effects of Substrate Temperature on the Final Shape of Evaporated Droplets of Aqueous Polymer Solution Lindsay Douglas, Qingying Chen, Scott Holmstrom When a drop of aqueous polymer solution dries on a solid substrate, the polymer is deposited in a coffee-ring shape on the surface of the substrate. This coffee-ring effect is due to the relatively high evaporation rate at the pinned three-phase contact line of the droplet that causes the aqueous polymer solution to move outward from the center of the drop in order to replenish the evaporated solvent at the edge. Decreasing the evaporation rate at the edge of the droplet can slow the outward flow of the fluid which then decreases the coffee-ring effect, thereby creating a more uniform polymer film on the substrate. This study investigates the effects of varying substrate temperatures on the final shape of an evaporated polymer droplet on a glass substrate. We have found that for different concentrations of the aqueous polymer solution, a decrease in substrate temperature is associated with a decrease in the coffee-ring effect and a more uniform polymer deposition. |
Friday, March 9, 2018 8:36AM - 8:48AM |
X55.00004: The Effects of Ambient Relative Humidity on the Final Shape of Evaporated Droplets of Aqueous Polymer Solution Qingying Chen, Lindsay Douglas, Scott Holmstrom When a drop of aqueous polymer solution dries on a solid substrate, the polymer is deposited in a ring-like shape. This shape is due to the relatively high evaporation rate at the pinned three-phase contact line of the droplet that causes the aqueous polymer solution to move outward from the center of the drop in order to replenish the evaporated solvent at the edge. This phenomenon is called the coffee-ring effect, which prevents a uniform deposition of the polymer from forming over the contact area of the drop on the substrate. Decreasing the evaporation rate of the drop weakens the outward flow which decreases the coffee-ring effect and enhances the uniformity of the polymer film. This study investigates the different shapes the dried drops have on a glass substrate due to their different concentrations of the solute and various ambient relative humidities. We have found that the coffee-ring effect can be decreased as the ambient relative humidity is increased. When the ambient relative humidity reaches 100%, the coffee-ring effect is almost eliminated. Moreover, higher concentration of the solute helps to deposit a thicker and more uniform polymer. |
Friday, March 9, 2018 8:48AM - 9:00AM |
X55.00005: Solvent-driven Infiltration of Polymer (SIP) into Nanoparticle Packings Neha Manohar, Bharath Venkatesh, Tianren Zhang, Robert Riggleman, Kathleen Stebe, Daeyeon Lee Polymer-infiltrated nanoparticle films (PINFs) are a new class of nanocomposite films with extremely high filler fractions (> 0.5) that have excellent mechanical properties. We introduce a one-step, room temperature method for PINF fabrication through solvent-driven infiltration of polymer (SIP) into nanoparticle (NP) packings from a bilayer film composed of a densely packed layer of NPs atop a polymer film. The bilayer film is exposed to solvent vapor, which leads to capillary condensation of solvent in the voids of the NP packing, followed by plasticization and infiltration of the polymer into the NP film. We study the effect of polymer-solvent interactions and the molecular weight of the polymer on the infiltration dynamics and the composition of SIP PINFs. We compare the dynamics of infiltration under vapor and liquid annealing. Using experiments and molecular dynamics simulations, we investigate two potential mechanisms of SIP, surface-mediated infiltration vs. dissolution. |
Friday, March 9, 2018 9:00AM - 9:12AM |
X55.00006: The Effect of Physical Confinement and Polymer-Particle Interaction on Polymer Capillary Rise Infiltration (CaRI) Dynamics Jyo Lyn Hor, Haonan Wang, Zahra Fakhraai, Daeyeon Lee Capillary rise infiltration (CaRI) relies on thermally-induced, capillarity-based polymer infiltration into voids of densely packed nanoparticle packings. During CaRI, the comparable length scales of the pore size in the nanoparticle packing and equilibrium polymer size confines the polymer. At the same time, the high volume fraction of nanoparticles creates high interfacial area between the polymer and particles. These phenomena may lead to deviation of polymer properties from its bulk values. In this study, we investigate the role of physical confinement and interfacial effects on polymer CaRI dynamics. We tune the polymer degree of confinement by varying the nanoparticle size constituting the packing and by using different molecular weight polymers. We tune the polymer-particle interaction by using a partially wetting and fully wetting system at comparable confinement, to systematically decouple individual effects on the polymer CaRI dynamics. We analyze the polymer CaRI dynamics based on the Lucas-Washburn model to estimate the viscosity of confined polymers. Physical confinement slows down the chain dynamics, which manifests in higher-than-bulk viscosity; whereas interaction affects the viscosity-temperature dependence of the dynamics under confinement. |
Friday, March 9, 2018 9:12AM - 9:24AM |
X55.00007: Line Tension of Twist-Free Carbon Nanotube Lyotropic Liquid Crystal Microdroplets on Solid Surfaces Evan Biggers, Vida Jamali Line tension, the force on a three-phase contact line, has been a subject of extensive research due to its impact on technological applications including nanolithography and nanofluidics. However, there is no consensus on the sign and magnitude of line tension, as it only affects droplets below the length scale dictated by the ratio of line tension to surface tension σ/τ. This ratio is related to the size of molecules in the system, which translates to a nanometer for conventional fluids. This ratio is orders of magnitude larger in lyotropic liquid crystal systems. Such systems form spindle-shaped elongated liquid crystal droplets in coexistence with the isotropic phase, with the droplets flattening when in contact with flat solid surfaces. We propose a method to characterize the line tension by fitting droplet shape to a model that incorporates interfacial forces and elastic deformation of the nematic phase. By fitting droplets of carbon nanotubes in chlorosulfonic acid to this model, we find that σ/τ ∼ −0.84 ± 0.06 μm, which is 2 orders of magnitude larger than what has been reported for conventional fluids, in agreement with theoretical scaling arguments. |
Friday, March 9, 2018 9:24AM - 9:36AM |
X55.00008: Packing of Bidisperse Nanospheres at a Fluid Interface Yige Gao, Paul Kim, Thomas Russell, David Hoagland Two-dimensional assembly of Brownian bidisperse nanosphere mixtures on a planar liquid surface was investigated by in situ scanning electron microscopy (SEM). The PEGylated silica nanospheres of different number and size ratios adsorbed strongly to an ionic liquid surface, spontaneously forming a mixed monolayer that organized according to the ratios selected. Several structural parameters for the monolayers were calculated from the SEM images, including translational order parameter T*, orientational order parameter <ψ6,k>, pair correlation function, correlation length, mixed triangular loop fraction, and probability of nearest neighbor number with respect to size for small, large, and all particles. A home-built liquid cell that allows variation of interfacial area caused particle jamming and unjamming. Our results show how the degree of order/disorder in spontaneously assembled bidisperse nanosphere monolayers can be controlled. |
Friday, March 9, 2018 9:36AM - 9:48AM |
X55.00009: Brownian motion under shear in a narrow gap studied by X-ray Photon Correlation Spectroscopy Taiki Hoshino, So Fujinami, Tomotaka Nakatani, Yoshiki Kohmura Brownian motions of nanoparticles dispersed in polyethyleneimine under shear in a narrow gap were studied using X-ray photon correlation spectroscopy. In this study, sample was sandwiched between facing surfaces, and shear was applied by moving one side of the substrate at a constant velocity. The gap between the surfaces was adjusted in the range of 10^1 to 10^2 nm and the changes in Brownian motion were investigated for various shear rates. X-rays irradiated from the side to the sample, the irradiation position was varied and the dynamics at each position was investigated. The time autocorrelation function of the scattering intensity obtained from the shear parallel direction and that from the shear orthogonal direction were analyzed separately. As a result, the latter was observed to be faster relaxation. By analyzing these data, the velocity gradient at each irradiation position was calculated. When the shear rate was slow, a uniform velocity gradient was observed. On the other hand, when the shear rate was increased, the velocity gradient became nonuniform, and in the vicinity of the moving interface, the velocity gradient was smaller than in other places. This can be considered to be a slip near the interface. Details of the experiments and analysis will be presented. |
Friday, March 9, 2018 9:48AM - 10:00AM |
X55.00010: Dissipative Particle Dynamic Mean-field Simulations of Phase Inversion Processing Polymer Thin Films with Hydrodynamic Interactions Huikuan Chao, Robert Riggleman Several important industrial processes rely on phase inversion membranes with microstructures on length scales from 10s of nm to several microns. The microstructures are typically formed during the flow of polymers and solvents, such as the formation of microstructures in phase inversion processing techniques. In the techniques, hydrodynamic effects often play a critical role in processing of polymer thin films. The thin films are cast as a polymer solution and then immersed in a bath of a non-solvent to the polymer. The hydrodynamics during the processing determine the final microscopic. However, hydrodynamic mechanisms at microscopic level that control the structures are far from fully understood and difficult to examine experimentally. In this talk, I will describe our work to develop computational tools capable of describing multiphase flows with hydrodynamic interactions. Our method is based on a dynamic mean-field theory with dissipative particle dynamics. We will present results from study of phase inversion processing of homopolymer solution thin films. Our study shows that the development of microstructures in the films depends on the hydrodynamic effects and can be manipulated by tuning factors including the polymer concentration and polymer/nonsolvent incompatibility. |
Friday, March 9, 2018 10:00AM - 10:12AM |
X55.00011: Role of Tacticity in Determining Polymer-Water Interactions Mesfin Tsige, Selemon Bekele, Ali Dhinojwala, Kshitij Jha We present quantification of the nature of hydrogen bond dynamics and functional group expression for three tactic forms of the common polymer, poly(methyl methacrylate) (PMMA). Using all-atom molecular dynamics simulations with validated potentials, the response at the water interface of isotactic, syndiotactic, and atactic forms was quantified in terms of hydrogen bond participation, interaction energies, and relaxation times. The relaxation and reorientation of carbonyl groups, the key determinant of tactic PMMA-water interactions, was also computed. We found that the atactic form exhibits cooperative effects based on hydrogen bond participation and carbonyl group orientation. Similarly, the isotactic form undergoes the largest change in orientation, which we hypothesize would be functionally reflected in contact angle hysteresis measurements. The observed subtle changes in physical interaction with water provide a platform for stereocomplexed coatings and membranes that can utilize differentials in participation rates, packing, and surface expression for designer adhesion, wettability, compatibility, and selectivity applications. |
Friday, March 9, 2018 10:12AM - 10:24AM |
X55.00012: Interfacial Structure of Poly(methylmethacrylate) in Contact with Tetrahydrofuran-Water Mixtures Saranshu Singla, Zhengnan Yang, Ali Dhinojwala Polymer nanoparticles of controlled size and narrow polydispersity are highly desirable in biomedical applications. Solvent-shifting is one of the promising methods to produce nanoparticles free of impurities, which involves the addition of a non-solvent to a pre-synthesized polymer in solution for precipitating nanoparticles. The mechanism by which the particles are formed is not understood, particularly the initial nucleation process during which the polymer chain undergoes conformational changes. In the present study, we investigate the coil-to globule transition induced by water (non-solvent) addition to poly(methylmethacrylate) (PMMA) solution in Tetrahydrofuran (THF). Contrary to 2-step coil-to-globule transition in dilute solution induced by temperature-shifting, we observe the formation of intermediate multi-chain aggregates (lifetime ~ days to months) before complete collapse of the chains into nanoparticles. To understand this, we probe the interface between PMMA thin film and THF-water mixtures using interface-sensitive sum frequency generation spectroscopy. A model explaining the formation of these intermediate aggregates will be discussed along with the interfacial structure. |
Friday, March 9, 2018 10:24AM - 10:36AM |
X55.00013: Binary and mixed brushes for dynamic surfaces Christian Pester, Kaila Mattson, David Lunn, Michael Brady, Gregory Su Binary and mixed brushes are comprised of two (or more), chemically distinct polymers randomly grafted to a surface in close proximity. This approach is considered a potent means to manufacture responsive surfaces with tunable physical properties. We highlight recent work in using chemically orthogonal Atom Transfer Radical Polymerization (ATRP) and Radical Addition Fragmentation Transfer polymerization (RAFT) to tailor such mixed surfaces, comprised of chemically disparate polymers covalently grafted to a silica surface. A combination of X-ray photoelectron spectroscopy, synchrotron hard (GISAXS) and soft resonant X-ray techniques (RSoXS), as well as Infrared Atomic Force Microscopy (AFM-IR) was used to provide evidence for responsiveness towards external stimuli. The choice of selective solvents for either of the two species resulted in reversible microphase segregation and can provide a direct pathway towards switchable surface properties. |
Friday, March 9, 2018 10:36AM - 10:48AM |
X55.00014: Universal strategy for stabilizing ultrathin polymer films for spin-on doping applications Reika Katsumata, Ratchana Limary, Bhooshan Popere, Yuanyi Zhang, Mingqi Li, Julia Kozhukh, Andrew Heitsch, Peter Trefonas, Rachel Segalman Stabilizing ultrathin films, in particular, avoiding dewetting is a critical requirement in electronics. To address this issue, a variety of approaches have been developed including self-assembled monolayers, surface-initiated polymerization, and end-functionalization of polymers. However, most of these approaches require either post-processing of the substrates or are applicable only to the specific combination of polymers and substrates. Herein, we introduce a mussel-inspired universal adhesive moiety, dopamine, as an end group to a boron-containing polymer, and demonstrate its application to spin-on doping on silicon. On semiconductor-relevant surfaces: Si-OH, SiOx, TiN, and Si3N4, ca. 15-nm thick films with the dopamine end group are more thermally stable at 230 oC for 30 min, while the control polymer films with carboxyl end group severely dewet. In addition, dosage of silicon with the dopamine-functionalized polymer is comparable or higher than that with the control polymer, demonstrating one of the promising applications of such conformal coatings. |
Friday, March 9, 2018 10:48AM - 11:00AM |
X55.00015: Surface and Interfacial Effects on Photo-Carrier Formation in Poly(3-hexylthiophene) Films Daisuke Kawaguchi, Shuhei Yamaguchi, Yudai Ogata, Keiji Tanaka Poly(3-hexylithiophene) (P3HT) is one of the representative semiconducting polymers and used in a thin film geometry in organic optoelectronic devices. To improve the device performance, it is important to understand a thinning effect on the carrier formation in P3HT thin films. Here we examined the carrier formation process in thin P3HT films prepared in various sample geometries such as free-standing, Si supported and sandwiched films based on temperature-dependent femtosecond transient absorption spectroscopy. It was found that polarons (P), which were free carriers, were directly generated from polaron pairs (PP) among all samples. The rate constant for the transition process from PP to P remained almost constant in a lower temperature region, and then simply increased with temperature above a certain temperature, which was defined as TPP→P. The TPP→P value depended on the sample geometry. As a general trend, the TPP→P values were in the ascending order of free-standing, supported and sandwiched films. While the TPP→P values for the free-standing and supported films were lower than the corresponding bulk one, that for the sandwiched film was higher. These results clearly indicate that the effects of surface and substrate interface make TPP→P lower and higher, respectively. |
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