Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R18: Polymers Adsorbed onto Solids - Interplay Among Structures, Dynamics, and Properties I |
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Sponsoring Units: DPOLY Chair: Bulent Akgun, Bogazici University Room: 277 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R18.00001: Polymer Conformation Under 1-Dimensional Rigid Symmetric Confinement James Pressly, Ronald Jones, Robert Riggleman, Karen Winey Understanding how polymer chain conformation is altered under nanoconfinement is critical for understanding polymer behavior in applications ranging from nanoscale lithography to polymer nanocomposites. Previous work associated with measuring polymer conformation under 1D confinement is limited to using ``open face'' thin films where at least one side of the confined dimension is a free surface. Studies have also been limited to measuring conformation changes parallel to the confining surfaces, which have recently been shown through simulations and theory to exhibit less change than the conformation perpendicular to the confining surface, leading to a partial and at times inconclusive understanding. Our study uses a new and unique sample geometry to simultaneously probe chain conformation parallel and perpendicular to the confining surfaces using small angle neutron scattering (SANS). The samples consist of long, narrow, and deep polymer filled channels that rigidly confine the polymer on both sides, preventing possible asymmetry due to one free and one obstructed confining surface. Here, we present our preliminary work in developing the sample geometry, performing SANS measurements, and establishing an analysis routine. [Preview Abstract] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R18.00002: Effect of Asymmetric Dynamics of Interfacial Polymers on Mechanical Response and Particle Dynamics of Polymer Nanocomposites Siyang Yang, Suresh Narayanan, Pinar Akcora Miscible polymer blends with different glass transition temperatures are known to create confined interphases between glassy and mobile chains. We recently showed that nanoparticles adsorbed with a high-T$_{g}$ polymer, poly(methyl methacrylate) (PMMA), and dispersed in a low-T$_{g}$ matrix polymer, poly(ethylene oxide) (PEO), exhibited a liquid-to-solid transition at temperatures above T$_{g}$’s of both polymers. Such mechanical adaptivity to temperature underlies the existence of dynamically asymmetric bound layers on nanoparticles, and their role on microscopic mechanical behavior. In this talk, we will present the mechanical responses of other polymer combinations with varying T$_{g}$ differences to reveal the stiffening mechanism. The strength of particle-polymer attractions, rigidity of adsorbed chains and the length of adsorbed chains are varied to explain unusual rheological responses of composites. The effect of the mobility of adsorbed chains on particle relaxations is measured. Confinement and dynamic coupling of polymer blends will be discussed by means of particle relaxations measured in X-ray photon correlation spectroscopy. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R18.00003: Unveiling the Dynamics of Self-Assembled Layers of Thin Films of PVME by Nanosized Relaxation Spectroscopy Sherif Madkour, Paulina Szymoniak, Andreas Schoenhals For thin polymer films, little is known about the dynamics of adsorbed layers. Here, Broadband Dielectric Spectroscopy (BDS) was utilized to investigate the glassy dynamics of thin films of a low M$_{\mathrm{W\thinspace }}$Poly (vinyl methyl ether) (PVME) (thicknesses: 7 - 160 nm). A recently developed nano-structured capacitor arrangement was employed; where a silicon wafer with nanostructured SiO$_{\mathrm{2}}$ nano-spacers, with heights of 35 nm and 70 nm, is placed on top of a thin film spin coated on an ultra-flat highly conductive silicon wafer. Further, PVME/SiO$_{\mathrm{2}}$ interactions were confirmed by contact angle measurements. For films with thicknesses smaller than 50 nm, BDS measurements showed two relaxation processes. The first process coincided, in its position and temperature dependence, with the $\alpha $-relaxation of bulk PVME, thus it was assigned to the $\alpha $-relaxation of a bulk-like layer. The second process showed a different temperature dependence and was ascribed to the relaxation of polymer segments adsorbed at the substrate. Both processes showed no thickness dependence. The results will be discussed in detail. To our knowledge, this is the first study of the segmental dynamics of an adsorbed layer in thin films. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R18.00004: Unraveling the Interfacial Interactions in Poly (2-vinylpyridine)/Silica Nanocomposites Dmitry Voylov, Adam Holt, Benjamin Doughty, Vera Bocharova, Harry Meyer III, Shiwang Cheng, Halie Martin, Mark Dadmun, Alexander Kisliuk, Alexei Sokolov Polymer nanocomposites (PNCs) have attracted a wide interest over the last several decades and deeper understanding of microscopic parameters controlling their properties is one of the major goals. Several studies demonstrated that the interfacial layer formed around nanoparticles governs macroscopic properties of PNCs. However, microscopic parameters controlling structure and dynamics in the interfacial layer remains poorly understood. Recently, it was shown [1] that the structure and dynamics of the interfacial layer depend strongly on molecular weight of polymer matrix, while underlying mechanism of this dependence is unclear. Here we present XPS and SFG studies of the interfacial interactions in poly (2-vinylpyridine)/silica nancomposites with different molecular weight of the polymer. Our results provide a clear experimental evidence that hydrogen bonding between polymer and nanoparticles decreases strongly with increase in molecular weight. We ascribe this observation to a frustration in packing of longer chains on the nanoparticles surface. This strongly affects dynamics and structure of the interfacial layer in the PNCs. 1. Cheng S. et al. Phys Rev Lett 116, 038302 (2016) [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R18.00005: Probing the Intercalation Behavior and Confining Effect of Clay Particles on an Amorphous Dendritic Polyester Kevin Meyers, Jeremy Decker, Sergei Nazarenko Hydroxylated dendritic hyperbranched polyesters (HBP) based on 2,2-bis-methylopropionic acid (bis-MPA) with an ethoxylated pentaerytriol core were combined with sodium montmorillonite clay (Na$^{+}$MMT) using water to generate a broad range of polymer clay nanocomposites (0 to 100{\%} wt/wt Na$^{+}$MMT). X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate the morphology of the clay galleries where intercalation was observed to be the dominant state. It was shown that the interlayer spacings changed with clay loading in 0.5 nm step-like increments which corresponded to a flattened conformation of the confined HBPs. Analysis with differential scanning calorimetry (DSC) showed a deviation in heat capacity,~$\Delta C_{p}$, with clay content at the~$T_{g\, }$from a two-phase trend which was attributed to the formation of an immobilized rigid amorphous fraction (RAF) in the interlayer spacings. This deviation also occurred in the step-like fashion which we attributed to the changes in the interlayer spacings. A simple series model was utilized to quantify the interlayer spacings based on the~$\Delta C_{p}~$values and showed good correspondence with the XRD results.~The RAF was quantified from changes in heat capacity with clay content and was verified by a novel positron annihilation lifetime spectroscopy (PALS) approach. PALS quantification of the RAF was possible through an analysis of changes in the hole size thermal expansivity of the nanocomposites as a function of clay composition. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R18.00006: Dynamically asymmetric polymer blends on nanoparticles: Effects on chain conformation, entanglement and particle mobility in nanocomposites Antonio Faraone, Erkan Senses, Pinar Akcora, Madhusudan Tyagi, Yimin Mao, Suresh Narayanan We study polymer nanocomposites with particles adsorbing a high glass-transition temperature (Tg) polymer, uniformly dispersed in a low-Tg miscible matrix, forming a dynamically asymmetric interphase. The collected results clarify the effect of the interfacial polymer on the conformation and entanglement of the matrix chains, as well as on the slow nanoparticle mobility. We found no significant effect of softness of the bound chains on the matrix chain conformation at particle concentrations up to 31 vol percent. A dilation of the reptation tube was observed when the interfacial polymer is glassy; such effect disappearing above Tg. Remarkably, the mobility of the nanoparticles is strongly influenced by the dynamical asymmetry in the interphase, resulting in a diffusive or sub-diffusive particle motion depending on the length-scale experimentally probed. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R18.00007: Abstract Withdrawn
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Thursday, March 16, 2017 9:24AM - 9:36AM |
R18.00008: Selective Electroless Nickel Plating on PMMA using Chloroform Pre-Treatment Nicholas Sipes In the past 5 years, we have discovered that chloroform promotes the adhesion of thin gold films to Poly(methyl methacrylate) surfaces. Based on this new understanding of the interaction of chloroform with PMMA and metal atoms, we were curious to see if chloroform would promote the adhesion of Nickel to PMMA deposited by electroless plating. My goal was to selectively electroless plate Nickel onto PMMA. Chloroform was spun-cast onto 1 inch square PMMA substrates. I used electrical tape to shield one half of the PMMA from the chloroform during spin-casting; this allowed for a direct comparison of treated vs. untreated. The samples were then put through hydrochloric acid and a series of baths provided by Transene Company Inc. to electrolessly deposit nickel on the sample. After many trials, there was a clear distinction in the adhesion strength of the Nickel to the plain PMMA surface vs. the chloroform pre-treated surface. Showing that it is possible to create chloroform sites via spin-casting for electroless nickel plating on PMMA opens up the challenge to better understand the chemistry taking place and to perfect the electroless plating process. [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R18.00009: How do ultrathin sheets attach to a fluid-fluid interface? Deepak Kumar, Joseph D. Paulsen, Thomas Russell, Benny Davidovitch, Dominic Vella, Narayanan Menon Thin elastic sheets when placed at the interface between immiscible fluids can lower the surface energy and hence act as surface active agents. Here we report experimental studies on the dynamics of attachment of ultrathin sheets to a fluid-fluid interface. A polymer film (thickness, t$=$30 to 500nm, and lateral size, W $\sim$ 1cm) is released in one of the liquid phases and driven towards the interface by gravity. At the interface, a slow initial nucleation process is followed by a rapid adsorption to the surface. Surprisingly, the three phase contact line remains stationary in the lab frame during most of the process, with the sheet bending sharply in the vicinity of the contact line. In the late stages of attachment, the sheet bends towards the interface and the contact line is observed to be moving. We find that at early times the attachment proceeds at a constant speed and compare this speed with scaling estimates. [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R18.00010: Visualization of the spatiotemporal elastohydrodynamic deformation of a compliant thin film under confinement Joelle Frechette Interfacial phenomena in soft matter display complex mesoscale behaviors that are qualitatively different from those encountered in stiff materials. Elastohydrodynamic deformation can cause lift and reduce friction during sliding and alter the rheological properties of colloidal particles. Elastohydrodynamic deformation also modifies the shape of approaching surfaces, a determining factor for the adhesion dynamics to wet or flooded surfaces. It is a challenge to measure simultaneously the hydrodynamic forces and the deformation, both necessary to understand how contact is reached and the coupling between deformation and viscous dissipation. \newline We will discuss the spatiotemporal deformation of an elastic film during the radial drainage of fluid from a narrowing gap. We observe that the elastic deformation of a thick film takes the form of a dimple and prevents full contact to be reached. With thin elastic film the stress becomes increasingly supported by the underlying rigid substrate and the dimple formation is suppressed, which allows the surfaces to reach full contact. For intermediate film thickness we observe shapes that are much more complex. We present a theoretical description that captures the effect of the film thickness on the elastic deformation and highlight the lag due to viscoelasticity. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R18.00011: Chain conformation near the buried interface in nanoparticle stabilized polymer thin films Justin Cheung, Deborah Barkley, Naisheng Jiang, Mani Sen, Maya Endoh, Jonathan Rudick, Tadanori Koga, Yugang Zhang, Oleg Gang, Guangcui Yuan, Sushil Satija, Daisuke Kawaguchi, Keiji Tanaka, Alamgir Karim It is known that when nanoparticles are added to polymer thin films, they often migrate to the film-substrate interface and form an ``immobile interfacial layer'', which has been believed as the origin of suppression of dewetting. We here report an alternative mechanism of dewetting suppression from the structural aspect of a polymer. Dodecane thiol-functionalized gold (Au) nanoparticles embedded in PS thin films prepared on Si substrates were used as a model. It was found that thermal annealing promotes irreversible polymer adsorption onto the substrate surface along with the surface migration of the nanoparticles. We also revealed that the surface migration causes additional nanoconfined space for the adsorbed polymer chains. As a result, the self-organization process of the strongly adsorbed polymer chains on the solid surface was so hindered that the chain conformations were randomized and expanded in the film normal direction. The resultant chain conformation allows the interpenetration between free chains and the adsorbed chains, promoting adhesion and hence stabilizing the thin film. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R18.00012: Interpenetration of thin polymer layers: effects of crosslinking and molecular weight Thomas A Seery, David Schwarzle, Oswald Prucker, Jurgen Ruehe, Mark Dadmun Schuh et al have recently reported on a general procedure for preparing robust multilayered polymer structures using C-H bond insertion reactions. Crosslinks formed in these processes can determine the interpenetration of subsequent layers. This molecular phenomenon impacts adhesion and interfacial sharpness. Designed polymer multilayers were prepared from sequential steps of spincoating followed by thermal or photochemical crosslinking steps. We have prepared thin multilayer films containing pendant benzophenones with layers that are alternately hydrophilic or hydrophobic where sharp interfaces are expected due to unfavorable enthalpic interactions between layers. These layered structures are compared to multilayers formed from d-PMMA and h-PMMA. Measurements of interfacial broadening before and after crosslinking for low and high molecular weights indicates that crosslinking does not prevent diffusion across the interface for lower molecular weights and that mobility is strongly molecular weight dependent. Film robustness was demonstrated as films could be removed by simply spinning the wafer with solvent prior to UV exposure. After UV exposure, multiple attempts to remove the layers in this manner were unsuccessful. Neutron reflectivity experiments were performed at NIST and ORNL. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R18.00013: Too Soft to Stick: Influence of Substrate Modulus on Gecko Adhesion Michael Wilson, Mena Klittich, Craig Bernard, Rochelle Rodrigo, Austin Keith, Peter Niewiarowski, Ali Dhinojwala The gecko adhesion system fascinates biologists and materials scientists alike for its strong, reversible, glue-free, dry adhesion. Geckos encounter a variety of surfaces in their natural habitats; tropical geckos, such as Gekko gecko, encounter hard rough tree trunks as well as soft flexible leaves. Gecko adhesion on a wide variety of hard surfaces has been extensively studied, however there has been no work focused on adhesion to soft surfaces. Here, we investigate for the first time the influence of substrate modulus on gecko adhesion using two different surfaces (cellulose acetate and polydimethylsiloxane). Understanding the limitations of the gecko system is critical for gecko experimental design as well as for the development of synthetic adhesives, particularly in the biomedical field. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R18.00014: Entropic segregation of short chains to the surface of a polydisperse melt Pendar Mahmoudi, Mark Matsen It is well understood that chains ends have an entropic preference for the surface of a polymer melt, and consequently the shorter chains of a polydisperse melt are favored at the surface. We study this effect for a bidisperse melt using numerical self-consistent field theory (SCFT). Semi-analytical approximations to the SCFT are derived for the concentration profiles resulting in simple expressions for the integrated excess or depletion of each component. [Preview Abstract] |
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