Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D22: Films at Liquid and Solid Interfaces |
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Sponsoring Units: DPOLY Chair: Thomas Salez, ESPCI Room: 407 |
Monday, March 3, 2014 2:30PM - 2:42PM |
D22.00001: Assembly of Graphene Oxide at Water/Oil Interfaces: Tessellated Nanotiles Thomas Russell, Zhiwei Sun, Tao Feng Graphene oxide (GO) was found to segregate at water/toluene interface when attractive polymer ligands, e.g. poly(styrene-b-2-vinylpyridine) or amine terminated polystyrene, were added to toluene phase. Functional groups on polymer ligand would interact with carboxyl groups on the GO through hydrogen bonding/electrostatic interactions. GO nanosheets migrated to the water/toluene interfaces, aligned parallel to the interface and occupied the free space at interface. A jammed GO thin film was obtained when the interfacial area was compressed. TEM images showed that GO nanosheets, like nanotiles, occupied the whole area of the interface and separated the water and toluene phase effectively. [Preview Abstract] |
Monday, March 3, 2014 2:42PM - 2:54PM |
D22.00002: Mechanical vibration of viscoelastic liquid droplets James Sharp, Victoria Harrold The resonant vibrations of viscoelastic sessile droplets supported on different substrates were monitored using a simple laser light scattering technique. In these experiments, laser light was reflected from the surfaces of droplets of high Mw poly acrylamide-co-acrylic acid (PAA) dissolved in water. The scattered light was allowed to fall on the surface of a photodiode detector and a mechanical impulse was applied to the drops using a vibration motor mounted beneath the substrates. The mechanical impulse caused the droplets to vibrate and the scattered light moved across the surface of the photodiode. The resulting time dependent photodiode signal was then Fourier transformed to obtain the mechanical vibrational spectra of the droplets. The frequencies and widths of the resonant peaks were extracted for droplets containing different concentrations of PAA and with a range of sizes. This was repeated for PAA loaded water drops on surfaces which displayed different values of the three phase contact angle. The results were compared to a simple model of droplet vibration which considers the formation of standing wave states on the surface of a viscoelastic droplet. [Preview Abstract] |
Monday, March 3, 2014 2:54PM - 3:06PM |
D22.00003: Water Interaction with Poly (methyl methacrylate) and Polyethylene Films Paul Jones, Thorin Kane, Brian Familo, Ross Netusil, Patrick Howard, Marie Romano, John St. Leger, Carolina C. Ilie We present herein the water desorption from the dipole oriented poly (methyl methacrylate) PMMA and from polyethylene. We analyze the desorption peaks for the ice and the bulk species. And if the water desorption is coverage dependent or not. Hyperchem calculations of molecular orbitals for both polymers are also discussed. The energy of desorption is obtained by employing the Arrhenius and Polany-Wigner equations. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D22.00004: Poroelastic characterization of ultrathin water purification membrane layers Edwin Chan The selective layer of pressure-induced water desalination membranes is a highly crosslinked aromatic polyamide ultrathin film that discriminates salt from water based on differences in diffusion coefficients. However, measuring transport properties of such ultrathin layer is difficult. In this presentation, poroelastic relaxation indentation (PRI) is demonstrated as a simple indentation based technique for measuring the transport properties of these ultrathin layers. Using PRI, the transport properties of four model crosslinked PA ultrathin films, synthesized via molecular layer-by-layer (mLbL), are characterized to show that the water diffusion coefficient, the volume fraction of water lost due to deswelling, as well as the intrinsic permeability can be simultaneously quantified using this one simple testing approach. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D22.00005: Stretching Ultra-thin Polymer Films on Water Yujie Liu, Alfred J. Crosby The mechanical properties of many materials, including polymers, are known to change as materials become dimensionally confined; however, the extent and mechanism for these transitions are difficult to quantify~due to~experimental challenges. Some methods allow a single property, such as the elastic modulus, to be determined, however relatively few, if any, allow the full constitutive relationship, including linear and nonlinear regimes, to be measured for thin, inherently fragile materials. Here, we describe a new method that overcomes these limitations. Specifically, we quantify the uniaxial tension stress-strain relationship for polystyrene (PS, MW$=$130kg/mol) and crosslinked polydimethylsiloxane (PDMS) elastomer as a function of film thickness (29nm-400nm for PS; 2$\mu $m-200$\mu $m for PDMS). We perform these measurements by floating thin films on a water surface and attaching one end of the film to a fixed boundary, and the other to a cantilever that is attached to a translating actuator. We use a reflective laser tracking system to measure~cantilever~displacement, hence the force, as a function of applied displacement. In addition to the elastic modulus as a function of thickness, we present observations of non-linear transitions and cyclic hysteresis as a function of strain. [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 3:42PM |
D22.00006: Perfect mixing of immiscible macromolecules at fluid interfaces Sergei Sheiko, Krzysztof Matyjaszewski, Vladimir Tsukruk, Jan-Michael Carrillo, Michael Rubinstein, Andrey Dobrynin, Jing Zhou Macromolecules typically phase separate unless their shapes and chemical compositions are tailored to explicitly drive mixing. But now our research has shown that physical constraints can drive spontaneous mixing of chemically different species. We have obtained long-range 2D arrays of perfectly mixed macromolecules having a variety of molecular architectures and chemistries, including linear chains, block-copolymer stars, and bottlebrush copolymers with hydrophobic, hydrophilic, and lipophobic chemical compositions. This is achieved by entropy-driven enhancement of steric repulsion between macromolecules anchored on a substrate. By monitoring the kinetics of mixing, we have proved that molecular intercalation is an equilibrium state. The array spacing is controlled by the length of the brush side chains. This entropic templating strategy opens new ways for generating patterns on sub-100 nm length scales with potential application in lithography, directed self-assembly, and biomedical assays. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 3:54PM |
D22.00007: Measuring the Height of Adsorbed Water Films With Atomic Force Microscopy Via Static Force Curves Jason Giamberardino Water Plays a crucial role in all biological processes and is present in almost all measurement scenarios. At the nanoscale, its presence has a large effect on measurement outcomes. Here, we present a measurement of the heights of adsorbed water films on a variety of commonly used substrate surfaces. The adsorbed films create an additional force, the capillary force, which must be added to the Van der Waals and repulsive forces to fully characterize the tip-sample interaction. Static force curves indicate the presence of this tertiary force, which depends on the height of the film, above a certain relative humidity. A fit of these curves then yields the height of the film present. [Preview Abstract] |
Monday, March 3, 2014 3:54PM - 4:06PM |
D22.00008: Structure of thin polystyrene films of varying tacticity adsorbed on solid substrates Yergou Tatek, Mesfin Tsige Atomistically detailed molecular dynamics simulations are used to investigate conformational properties of thin films of polystyrene (PS) adsorbed on two types of solid substrates. The substrates considered are graphite and hydroxylated silica which are known to be of different phobicity. The conformation of the PS chains was studied in terms of side chains, backbone and end group concentration and orientation. As expected, the films structure is different in all the three regions which are the two interfaces and the bulk of the film. Moreover, the film structural properties are also dependent on the nature of the substrate. We have also investigated the effect of chain tacticity on the films conformational properties. Preliminary results show the absence of a strong correlation between tacticity and structure. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D22.00009: Fabrication and Theoretical Evaluation of Microlens Arrays on Layered Polymers Tom Oder, Michael McMaster, Corey Merlo, Camron Bagheri, Clayton Reakes, Joshua Petrus, Dingqiang Li, Michael Crescimanno, James Andrews Arrays of microlens were fabricated on nano-layered polymers using reactive ion etching. Semi hemispherical patterns with diameters ranging from 20 to 80 micrometers were first formed on a thick photoresist film that was spin-coated on the layered polymers using standard photolithographic process employing a gray scale glass mask. These patterns were then transferred to the polymers using dry etching in a reactive ion etching system. The optimized etch condition included a mixture of sulfur hexafluoride and oxygen, which resulted in an etch depth of 5 micrometers and successfully exposed the individual sub-micron thick layers in the polymers. Physical characterization of the microlens arrays was done using atomic force microscope and scanning electron microscope. We combine basic physical optics theory with the transfer matrix analysis of optical transport in nano-layered polymers to address subtleties in the chromatic response of microlenses made from these materials. In particular this method explains the len's behavior in and around the reflection band of the materials. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D22.00010: The mechanical properties of supported thin polystyrene films Peter Chung, Emmanouil Glynos, Peter Green The mechanical properties of supported thin polystyrene films with thicknesses in the range of 100 nm to 1 micron were studied by atomic force microscopy (AFM) nanoindentation measurements. The effective modulus of the 1 micron thick PS film at small indentation depths, in the range of few nanometers ($\sim$3 nm), was independent of frequency (indentation rate) in the range we studied. On the other hand, the effective modulus of thinner PS films showed an increase in the modulus with decreasing film thicknesses and this enhancement was frequency-dependent. Finite element analysis revealed that the stress field induced by nanoindentation propagates a few hundred nanometers into the film even with only a few nanometers of indentation, and the enhancement in the effective modulus stems from the underlying hard substrate. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D22.00011: Structures and Elastic Moduli of Polymer Nanocomposite Thin Films Hongyi Yuan, Alamgir Karim Polymeric thin films generally possess unique mechanical and thermal properties due to confinement. In this study we investigated structures and elastic moduli of polymer nanocomposite thin films, which can potentially find wide applications in diverse areas such as in coating, permeation and separation. Conventional thermoplastics (PS, PMMA) and biopolymers (PLA, PCL) were chosen as polymer matrices. Various types of nanoparticles were used including nanoclay, fullerene and functionalized inorganic particles. Samples were prepared by solvent-mixing followed by spin-coating or flow-coating. Film structures were characterized using X-ray scattering and transmission electron microscopy. Elastic moduli were measured by strain-induced elastic buckling instability for mechanical measurements (SIEBIMM), and a strengthening effect was found in certain systems due to strong interaction between polymers and nanoparticles. The effects of polymer structure, nanoparticle addition and film thickness on elastic modulus will be discussed and compared with bulk materials. [Preview Abstract] |
Monday, March 3, 2014 4:42PM - 4:54PM |
D22.00012: Neutron Reflectivity Measurement of Polymer-Surface Interaction Richard Sheridan, Sara Orski, Ronald Jones, Kathryn Beers Liquid adsorption chromatography at critical conditions (LACCC) is a method of macromolecular separation that is simultaneously promising and problematic. There is a large parameter space for customization of surface properties and the ternary optimization of solvent, solute, and surface necessary to find ideal separation conditions. By creating 2D model substrates using polymers grafted to the interface, we create a system in which the adsorption process near critical conditions can be observed directly. In this way, we gain fundamental insight into the contribution of the interface to the LACCC separation process, which will be useful in the rational design of stationary phases for this technique. Thin polymer film swelling is in principle observable by a number of techniques, such as ellipsometry or quartz crystal microbalance with dissipation. However, we intend to observe the nanometer-scale shifts in polymer conformation at low grafting density. Therefore, we use neutron reflectivity to observe the process in the initial stages because of its relatively high contrast and sensitivity. We demonstrate this technique by emulating published polystyrene LACCC conditions in cyclohexane and dimethylformamide. We then calculate an interaction parameter directly related to the free energy of adsorption, and compare it to the adsorption partition coefficient derived from the literature LACCC experiment. These direct measurements are critical for description of a wide variety of interfacial dynamic processes. [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:06PM |
D22.00013: Using multivalency to tailor the superselective binding of polymers on substrates Nicholas Tito, Daan Frenkel Multivalency is a microscopic design concept in which a single nanoscopic entity contains multiple ligands, each of which may bind to multiple receptors on another entity. A useful property of many multivalent systems is ``superselectivity,'' where the fraction of the multivalent species bound to their complementary receptors grows sharply with the total number of receptors available. For example in the past two decades, multivalency has been exploited to develop DNA-coated nanoparticles that self-assemble into aggregates over an extremely narrow temperature window. In this talk, we use analytic and self-consistent field theories to explore the binding of multivalent polymers to receptors on a flat substrate. Discussion will focus on how the sequence, number, and binding strength of ligands along the polymer chain can be used to tune the superselectivity of the system. Comparison with recent experiments on model systems will be presented as time permits. [Preview Abstract] |
Monday, March 3, 2014 5:06PM - 5:18PM |
D22.00014: Enhanced Molecular Dynamics in the Near-Surface Region of Polystyrene Thin Films Observed with $\beta$-NMR Iain McKenzie, Chad R. Daley, Robert F. Kiefl, C.D. Phil Levy, W. Andrew MacFarlane, Gerald D. Morris, Matt R. Pearson, Dong Wang, James A. Forrest Beta-detected nuclear spin relaxation of $^8\mathrm{Li}^+$ has been used to probe the depth dependent molecular dynamics in high- and low-molecular-weight deuterated polystyrene (PS-d8). In both samples, the average nuclear spin-lattice relaxation rate, $1/T_1^{\mathrm{avg}}$, is depth independent below $\sim$200~K. However, above this temperature $1/T_1^{\mathrm{avg}}$ increases above the bulk value within several nanometers of the surface. These results provide the most direct evidence for enhanced molecular-level mobility near the free surface of glassy polymers and suggest the polymer fluctuation rate decreases approximately exponentially with distance from the free surface, returning to bulk behavior for depths greater than $\sim$10~nm. [Preview Abstract] |
Monday, March 3, 2014 5:18PM - 5:30PM |
D22.00015: Brewster Angle Microscopy and Characterization of Polyvinylidene Fluoride (PVDF) Based Langmuir Films Timothy Reece The behaviors of ferroelectric polymer Langmuir films are observed with the use of a Brewster angle microscope. In general, Langmuir films form a single molecular layer on water because they are often good amphiphiles. Since the polymer Polyvinylidene Fluoride (PVDF) is not a true amphiphile, parameters like solution concentration, water pH, and molecular weight may have an effect on film behavior and quality. Similar polymers with hydrophobic groups are also investigated. [Preview Abstract] |
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