Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session A9: Symposium Honoring Ed Kramer - Mechanics and DynamicsFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Russell Composto, University of Pennsylvania Room: 268 |
Monday, March 13, 2017 8:00AM - 8:36AM |
A9.00001: Chasing Extreme Polymer Morphologies with Ed Invited Speaker: Glenn Fredrickson I was privileged to have a seventeen year friendship and scientific collaboration with Edward J. Kramer that produced 55 papers and countless student and postdoc co-advisements. This talk will discuss our last project together; an ongoing research program to achieve thermoplastic polymer materials that are uniquely hard, tough, and elastic, with moduli greater than 100 MPa and elastic recovery greater than 0.9 at strains of 1 or more. The targeted materials are based on an A(BA')n mikto-arm block copolymer architecture, and alloys of these molecules with A homopolymer. The molecular design of the miktopolymer was optimized using self-consistent field theory and the materials realized in a polystyrene (A)-polyisoprene (B) system. TEM, SAXS, and tensile mechanical tests were used to validate the designs and probe microstructure/mechanics relationships. An unexpected discovery was the emergence of a new structured disordered phase -- the bricks and mortar phase --in which the A domains remain discrete at up to a volume fraction of 0.7. Field-theoretic simulations have been used to understand the origins of this new fluctuation-stabilized equilibrium phase, which has no precedent in the polymer physics literature. [Preview Abstract] |
Monday, March 13, 2017 8:36AM - 9:12AM |
A9.00002: Multi-Scale Structure of Coacervates formed by Oppositely Charged Polyelectrolytes Invited Speaker: Michael Rubinstein We develop a scaling model of coacervates formed by oppositely charged
polyelectrolytes and demonstrate that they self-organize into multi-scale
structures. The intramolecular electrostatic interactions in dilute
polyanion or polycation solutions are characterized by the electrostatic
blobs with size $D_{-}$ and $D_{+}$ respectively, that repel neighboring
blobs on the same chains with electrostatic energy on the order of thermal
energy $kT$. After mixing, electrostatic intramolecular repulsion of
polyelectrolytes with higher charged density, say polyanions, keeps these
polyanions in coacervates aligned into stretched arrays of electrostatic
blobs of size $D_{-} |
Monday, March 13, 2017 9:12AM - 9:24AM |
A9.00003: Network Confinement and Heterogeneity Slows Nanoparticle Diffusion in Polymer Gels Emmabeth Parrish, Matthew Caporizzo, Russell Composto Nanoparticle (NP) diffusion was measured in polyacrylamide gels (PAG) with a mesh size comparable to NP size, 20nm. The confinement ratio (CR), NP diameter/mesh, increased from 0.4 to 3.8 by increasing crosslinker density and 0.4 to 2 by adding acetone, which collapsed PAG. In all gels, NPs either became localized (\textless 200nm) or diffused microns, as measured by single particle tracking. Mean squared displacements (MSD) of mobile NPs decreased as CR increased. In collapsed gels, the localized NP population increased and MSD of mobile NPs decreased compared to crosslinked PAG. For all CRs, van Hove distributions exhibited non-Gaussian displacements consistent with intermittent localization of NPs. The non-Gaussian parameter increased from a maximum of 1.5 for crosslinked PAG to 5 for collapsed PAG, consistent with greater network heterogeneity. Diffusion coefficients, D, decreased exponentially as CR increased for crosslinked gels, but in collapsed gels D decreased more strongly, suggesting CR alone was insufficient to capture diffusion. Collapsing the gel resulted in an increasingly tortuous pathway for NPs, slowing diffusion at a given CR. Understanding how gel structure affects NP mobility will allow the design of gels with improved ability to separate and release molecules. [Preview Abstract] |
Monday, March 13, 2017 9:24AM - 9:36AM |
A9.00004: The First Normal Stress Difference in Waterborne Paints Thickened by Hydrophobically Ethoxylated Urethane (HEUR) Rheology Modifier: A Simplified Phase Diagram Tirtha Chatterjee, Antony Van Dyk, Valeriy Ginzburg, Alan Nakatani Since their invention in the 1970s, hydrophobically ethoxylated urethane (HEUR) associative thickeners are widely used to modify the rheology of waterborne paints. While their flow curves (viscosity vs. shear rate) and microstructure have been studied extensively in recent years (1-4), there is surprisingly little information on the paint normal stress under application conditions. However, understanding of normal stress behavior is critical for many applications such as brush drag and spatter. In this work we will demonstrate that in HEUR-based paints the first normal stress difference (N1) is controlled by two factors: (a) adsorption of HEUR molecules on latex particles and (b) ability of non-adsorbed HEUR to form transient bridges between particles with HEUR shells. By controlling these two effects, one can design a paint formulation with targeted N1 behavior (positive or negative N1 under high shear). Finally, a simplified phase diagram will be presented connecting formulation composition-microstructure- and N1 behavior. The results would serve as guidelines to formulate paints to meet the specific customer needs. 1. Beshah, K., et. al.; 2013, Macromolecules, 46(6), 2216. 2. Chatterjee, T., et. al.; 2014, Macromolecules, 47(3), 1155. 3. Van Dyk, A.K., et. al.; 2015, Macromolecules, 48(6), 1866. 4. Ginzburg, V.V., et. al.; 2015, Macromolecules, 48(21), 8045. [Preview Abstract] |
Monday, March 13, 2017 9:36AM - 9:48AM |
A9.00005: Thickness Dependence of Failure in Ultra-thin Glassy Polymer Films Reed Bay, Shinichiro Shimomura, Yujie Liu, Mark Ilton, Alfred Crosby The physical properties of polymer thin films change as the polymer chains become confined. Similar changes in mechanical properties have been observed, though these critical properties have only been explored a limited extent and with indirect methods. Here, we use a recently developed method to measure the complete uniaxial stress strain relationship of polymer thin films of polystyrene films (PS, Mw$=$130kg/mol, 490kg/mol, and 853kg/mol) as a function of thickness (20 nm-220nm). In this method, we hold a `dog-bone' shaped film on water between a flexible cantilever and a movable rigid boundary, measuring force-displacement from the cantilever deflection. From our measurements, we find that the modulus decreases as the PS chains become confined. The PS thin films exhibit ``ideal perfectly plastic'' behavior due to crazing, which differs from the typical brittle response of bulk PS. The draw stress due to crazing decreases with film thickness. These results provide new fundamental insight into how polymer behavior is altered due to structural changes in the entangled polymer network upon confinement. [Preview Abstract] |
Monday, March 13, 2017 9:48AM - 10:00AM |
A9.00006: Statistical Mechanical Theory of Coupled Slow Dynamics in Glassy Polymer-Molecule Mixtures Rui Zhang, Kenneth Schweizer The microscopic Elastically Collective Nonlinear Langevin Equation theory of activated relaxation in one-component supercooled liquids and glasses is generalized to polymer-molecule mixtures. The key idea is to account for dynamic coupling between molecule and polymer segment motion. For describing the molecule hopping event, a temporal casuality condition is formulated to self-consistently determine a dimensionless degree of matrix distortion relative to the molecule jump distance based on the concept of coupled dynamic free energies. Implementation for real materials employs an established Kuhn sphere model of the polymer liquid and a quantitative mapping to a hard particle reference system guided by the experimental equation-of-state. The theory makes predictions for the mixture dynamic shear modulus, activated relaxation time and diffusivity of both species, and mixture glass transition temperature as a function of molecule-Kuhn segment size ratio and attraction strength, composition and temperature. Model calculations illustrate the dynamical behavior in three distinct mixture regimes (fully miscible, bridging, clustering) controlled by the molecule-polymer interaction or chi-parameter. Applications to specific experimental systems will be discussed. [Preview Abstract] |
Monday, March 13, 2017 10:00AM - 10:12AM |
A9.00007: Dynamic Polymer Brush using Amphiphilic Block Copolymers Hideaki Yokoyama, Hirokazu Tanoue, Manabu Inutsuka, Kohzo Ito, Norifumi Yamada A layer of polymer chains tethered by one end to a surface is called polymer brush and known to show various unique properties such as prevention of protein adsorption and anti-fouling activity. The surface segregation phenomena of copolymers with surface-active blocks should be useful for preparing such a brush layer in spontaneous process. We report hydrophilic polymer brushes formed at the interface between water and hydrophobic polymer matrix by the segregation of amphiphilic diblock copolymers blended in the matrix. In this system, while the hydrophilic block with high surface energy avoids air surface it segregate to cover the interface between hydrophobic PDMS and water. The structures of formed brush layers at D$_{2}$O/polymer interfaces were observed by neutron reflectometry (NR). The brush density was calculated to be even comparable the density of typical polymer brushes fabricated by the “grafting-from” method. We further studied the kinetics of dynamic polymer brush formation using Quartz Crystal Microbalance (QCM) and time-resolved NR. We will discuss the detail of the brush forming mechanism in the presentation. [Preview Abstract] |
Monday, March 13, 2017 10:12AM - 10:24AM |
A9.00008: High Rate Micromechanical Behavior of Grafted Polymer Nanoparticle Films Edwin Thomas We report the ultra high strain rate behavior of films comprised of polymer grafted nanoparticles (NPs) and compare the results to homopolymer films. The films are formed by flow coating a suspension of polystyrene (PS) chains of 230 kg/mol grafted to 16nm diameter SiO$_{\mathrm{2\thinspace }}$at a graft density of \textasciitilde 0.6 chains/nm$^{\mathrm{2}}$ resulting a film with 1 vol {\%} SiO$_{\mathrm{2}}$. Films of 267 kg/mol PS were also flow coated and both films were impacted at velocities 350-700 ms$^{\mathrm{-1}}$ using 3.7 micron SiO$_{\mathrm{2\thinspace }}$projectiles to achieve increments in kinetic energy (KE) of 1:2:4. The KE of the projectiles before and after penetration was measured to determine the penetration energy. TEM and SEM suggest the projectile initially induces plastic flow due to the adiabatic temperature rise from impact. As the projectile deforms the film, the lower magnitude, biaxial stress state in the peripherial regions causes material microvoid formation and initiation of craze growth in the radial and tangential directions. The anchoring of the grafted polymer chains to the NPs increases the penetration energy relative to the pure homopolymer by 50{\%} and the films capacity to delocalize the impact by 200{\%}. These results suggest that highly grafted NP films may be useful in lightweight protection systems. [Preview Abstract] |
Monday, March 13, 2017 10:24AM - 10:36AM |
A9.00009: Quantifying Crazing Deformation in Ultrathin Polymer Films Yang Jiao, Ming-Siao Hsiao, Andrew Gillman, Philip Buskohl, Lawrence Drummy, Richard Vaia The mechanical stability of ultrathin polymer films is not only of fundamental importance, but also critical to applications like nanoelectronics. The fragile nature of ultrathin films and sensitivity to the environment, present difficulties to quantifying mechanical properties, and thus discrepant results may be found in the literature. Here, we examine the plastic deformation of polystyrene (PS) films (20-300 nm) using an elastomer support to delay stress localization. Adhesion to and geometric constraint of the elastic substrate suppresses stress localization within the thin film, impeding film rupture, and allowing measurements of craze initiation and width evolution. Additionally, orthogonal compressive buckling provides an independent measurement of film stiffness. For PS, the strain onset of craze widening increases with molecular weight, and decreases with film thickness. These measurements are consistent with prior reports using the copper-grid technique and the ultrathin film tensile test; and confirm the molecular weight-dependence of fibril stability and the film thickness-dependence of break stain. Confirmation of this platform provides an alternative technique to assess deformation mechanisms of emerging materials, such as assemblies of polymer grafted nanoparticles. [Preview Abstract] |
Monday, March 13, 2017 10:36AM - 10:48AM |
A9.00010: Direct Measurement of Crazing Mechanics in Polystyrene Thin Films: Molecular Weight Effects Shinichiro Shimomura, Reed Bay, Mark Ilton, Alfred Crosby Mechanical properties of polymer thin films are critical to various applications such as protective coatings, electronic devices, and separation membranes. Although methods for measuring the structure and some physical properties, such as T$_{\mathrm{g}}$, of polymer thin films have been well established, measuring mechanical properties of thin films has not been fully developed and has been largely limited to extremely small strains and complex stress distributions. To overcome these limitations, we have recently introduced a direct measurement technique for quantifying the complete uniaxial stress-strain relationship for polymer thin films. Here, we use `dog-bone' shaped thin films of polystyrene (PS) to quantify the change in mechanical response as a function of molecular weight. We observe a nonlinear stress-strain relationship, resembling ideal plastic-like behavior, associated with the onset of crazing. We will discuss how the onset stress and critical strain to failure changes as a function of molecular weight. These changes, and the alignment of craze fibrils, are discussed in the context of how entanglement density is altered for confined thin films. These results provide new insight into fundamental molecular physics for polymer thin films. [Preview Abstract] |
Monday, March 13, 2017 10:48AM - 11:00AM |
A9.00011: X-ray scattering to probe cracks in rubbers Costantino Creton, Quentin Demassieux, Daniel Berghezan Natural rubber is a well-known very tough elastomer and its toughness is generally attributed to its aptitude to crystallize under strain. Yet the mechanism linking the extent of strain induced crystallization to the toughness gamma is still unclear. We mapped by scanning microbeam X-ray diffraction (20 microns resolution), the strain–induced crystallization near the crack tip of highly crosslinked and carbon-black filled natural rubbers. Experiments were carried out on static cracks loaded at different values of energy release rates G and for different filler and crosslinker concentrations. We specifically investigated the effect of the crosslinking density, the effect of thermal (oxygen-free) aging and the effect of temperature (between 23 and 100 °C). Several novel findings are reported : a significant amount of crystallization was still present at the crack tip at 100°C, thermal aging (in the absence of oxygen) greatly reduces the amount of crystallization at the crack tip without much effect on the room temperature resistance to fatigue crack propagation of the material, and an increase in crosslinking density reduces the extent of crystallinity at the crack tip for the same applied G. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700