Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B50: UKPPG/DPOLY Polymer Lecture Exchange: Advances in Film Formation and Chain DynamicsFocus
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Sponsoring Units: DPOLY Chair: Bryan Boudouris, Purdue University Room: BCEC 252B |
Monday, March 4, 2019 11:15AM - 11:51AM |
B50.00001: Drying Blends of Polymer Colloids: How to Harness Physics to Control Film Formation Invited Speaker: Ignacio Martin-Fabiani Colloidal self-assembly methods, using particles suspended in a solvent as the building blocks, have been recently proposed as a single-step alternative for obtaining surfaces “on demand”.1 We recently proved experimentally how in blends of polymer colloids of two different sizes, small particles can segregate during drying into a layer on top of the larger particles.2 The moving interface causes a density, and hence a pressure, gradient in the drying film, which pushes larger particles away from the moving interface faster than it pushes smaller particles. By using stimuli-responsive particles, which swell with increasing pH, it is possible to switch stratification on and off by just changing the pH of the initial dispersion.3 For a certain size, stratification is supressed because of the increased solids content, which reduces particle mobility and reduces the osmotic pressure gradient. This type of self-assembly allows the independent control of the properties of the top and the bottom of the final film, dictated by the functionality of the large and small particles. Modelling shows it is a really strong and reliable effect, taking place for a wide range of particle size ratios and evaporation rates. However, agreement with experiments is limited, because of coffee-ring effects and Marangoni flows that are not usually present in models. In this talk, I will discuss the progress we made in this field and how we can harness the Physics of polymer colloid systems to control the final film structure towards a certain application. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B50.00002: Programming surface energy driven Marangoni convection to pattern polymer films Christopher Ellison The Marangoni effect describes how fluid flows in response to gradients in surface energy. We recently developed a method for photochemically preprograming spatial surface energy patterns in glassy polystyrene (PS) thin films. UV irradiation through a mask selectively dehydrogenates the PS, thus increasing surface energy in the UV exposed regions compared to the unexposed regions. After heating the film to the liquid state, transport of polymer occurs from regions of low surface energy to regions of high surface energy. This method can be harnessed to rapidly manufacture polymer films possessing prescribed three-dimensional topographies reflective of the original light exposure pattern without solvent washes or etching procedures. To better understand this phenomenon, a theoretical model will be presented that reveals the physics of this process, its limits and ways to apply it efficiently for various target metrics. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B50.00003: Influence of Hydrodynamic Interactions on Stratification in Drying Mixtures Antonia Statt, Michael Howard, Athanassios Panagiotopoulos It is desirable to control the structure of dried multicomponent films for many technologies, but there is an incomplete theoretical understanding of how evaporation affects film structure. Recent experiments1 showed that mixtures of small and large colloids unexpectedly stratify with the small colloids counterintuitively on top of the large colloids. Stratification can be modeled without hydrodynamic interactions (HIs) using dynamic density functional theory, but it was recently suggested2 that HIs cannot be reasonably neglected. We investigated the influence of HIs on stratification using nonequilibrium simulations of polymer films with explicit and implicit solvent models.3 The short chains stratified on top of the long chains in the implicit solvent (no HIs) in agreement with previous theoretical models and simulations. However, the explicit solvent model did not stratify at the same drying conditions due to HIs. Our work shows that it is critical to include HIs into models for drying films. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B50.00004: Strategies to improve the unconfined melt electrospinning process via incorporation of ionically conductive particles Elnaz Shabani, Chengxi Li, Rebecca j Komer, Laura Clarke, Jason R Bochinski, Russell E Gorga, Brenton Boland, Neelam Sheoran By utilizing a sharp-edged flat plate, multiple parallel jets can be electrospun spontaneously from unconfined polymer melts. In this work polyethylene was electrospun from a thin film of the polymer melt heated on an electrically-grounded flat plate. This technique can produce fibers with a throughput rate of about 50 mg/min without the possibility of clogging which frequently happens in traditional single needle electrospinning due to high viscosity of polymer melts. The effect of increased melt conductivity through salt additives on fiber diameter was studied to present a method for fabrication of smaller diameter fibers from highly- insulating polymer thermoplastics. Also, The environmental temperature, specifically in the spin-line shows to have a significant impact on the fiber diameter and the spinning process. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B50.00005: Creating thin film compositional polymer libraries using electrospray deposition Kristof Toth, Gregory Doerk, Kevin G. Yager, Chinedum Osuji Electrospray deposition (ESD) enables the growth of polymer thin films in a precise and continuous manner by the delivery of sub-micron droplets of dilute polymer solutions to a heated substrate. By combining ESD with programmable motor control and gradient solution pumping in a first-of-its-kind user tool at the Center for Functional Nanomaterials at Brookhaven National Laboratory, we show the ability to create one or two-dimensional compositional gradient nanoscale films via ESD. These capabilities make it possible to construct thin film multicomponent “libraries” on a single substrate to rapidly and systematically characterize composition-dependent properties, in particular, thin films involving homopolymer and block copolymer (BCP) blends. We report the design, construction, and validation of a gradient ESD tool which allows users to carefully control the jet stability, flow composition, spray position, and substrate temperature. Paired with synchrotron small angle X-ray scattering (SAXS), this tool forms an integral part of a new platform for high-throughput, autonomous characterization and design of self-assembling polymer blends as well as functional soft materials more generally. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B50.00006: Understanding the Deformation of Polymer Thin Films Under Hydration Peter Dudenas, Adam Z Weber, Ahmet Kusoglu Understanding the impact of interfaces and surfaces on hydrophilic/amphiphilic polymers including ionomers is of increasing interest as functional polymer coatings and thin-film devices become more ubiquitous. In these thin-film systems, confinement and interfacial energy impact a variety of properties including Tg, modulus, and morphology; the degree of hydration will also significantly impact these properties. Because of this, the characterization of mechanical properties for polymer thin films and networks under hydration remains a challenge. Here, we report the swelling-induced deformation of model hydrogel and block copolymer films as a function of thickness, cross-linking, and surface functionalization to understand the effect of confinement and surface interactions on polymer swelling and swelling-induced stresses. A cantilever bending method is used to characterize the mechanical response which is correlated to morphology using in-situ grazing incidence x-ray scattering. The results and techniques are applicable to understand the structure-functionality of a wide variety of polymers, including hydrogels, ion-conducting polymers for energy conversion, and block copolymers. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B50.00007: AFM Observation of the Movements of Single Linear Chains in a Precursor Film of a Spreading Polymer Blend Melt Yasuhiro Watanabe, Jiro Kumaki We have successfully visualized the movements of single chains in a precursor film of a spreading polymer melt on a substrate at the molecular level by atomic force microscopy (AFM). A polymer melt spreading on a substrate forms a precursor film with a thickness comparable to a monolayer at the flow front. Previously, Sheiko and coworkers successfully observed the movements of polymer brush molecules in the precursor film of a spreading melt (Phys. Rev. Lett. 2004, 93, 206103), however, those of conventional linear polymers have not yet been observed due to the limited resolution of the present AFM instruments. We observed a mixture of a poly(methyl methacrylate) (PMMA) oligomer with a small amount of a high-molecular-weight isotactic (it) PMMA polymer, and successfully observed the movements of the it-PMMA polymer chains flowing in the precursor film of the spreading melt at the molecular level. The movements of the individual PMMA chains will be discussed in detail. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B50.00008: Lattice Self-Consistent Field Calculations of Ring Polymer Brushes Qiang Wang, Wenjuan Qiu, Baohui Li We report the first systematic study using lattice self-consistent field (LSCF) calculations of ring homopolymer brushes grafted onto a flat and homogeneous surface and immersed in an explicit and athermal solvent, which are either uncompressed, compressed by a flat and impenetrable surface, or compressed by an identical brush.[1] Our results clearly show that ring brushes are slightly less stretched than, thus nearly but not completely identical to, the “equivalent” linear brushes having half the chain length and double the grafting density. Our LSCF results are consistent with the molecular simulation results reported in the literature[2,3], except the previous finding that the normal pressure of two opposing ring brushes is only half of the “equivalent” linear brushes at melt density[3]. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B50.00009: Comprehensive scaling theory for entanglement in melts and solutions of flexible and stiff polymer chains Scott Milner The entanglement length Ne is a key parameter for all entangled polymer fluids, for which no comprehensive scaling theory yet exists. We have pieces of a theory; the Lin-Noolandi (LN) argument predicts Ne scaling for flexible chains that agrees with data on melts. There are arguments for how Ne should depend on polymer volume fraction, but which are not obviously consistent with LN. Morse scaling describes entanglement for stiff chains, consistent with data. Everaers proposed an ansatz that Ne depends only on “arclength concentration”, as if chains were uncrossable threads. This ansatz is consistent with simulation of bead-spring chains but not with LN, it has no role for packing length, the central parameter in LN scaling. We propose a comprehensive scaling theory which includes LN in one limit, thread ansatz in another, and reduces to Morse scaling for stiff chains. Our new ingredient is the observation that the typical distance of closest approach between two chains is governed by packing length or chain diameter, whichever is larger. If a chain is sufficiently flexible and bulky, the packing length is relevant; but for stiffened bead-spring chains without sidegroups, the packing length is likely smaller than the chain diameter, so thread scaling applies. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B50.00010: Effect of Polymer Architectures on the Entanglement of Combs and Bottlebrushes Heyi Liang, Benjamin J. Morgan, Guojun Xie, Michael Martinez, Krzysztof Matyjaszewski, Sergei Sheiko, Andrey Dobrynin We study correlations between the entanglement plateau modulus and architecture of graft polymers in a melt. To distinguish between two types of graft polymers – combs and bottlebrushes – we introduce the crowding parameter Φ, which describes mutual interpenetration of the neighboring macromolecules. In comb systems, both the backbones and sparsely grafted side chains are coiled and allow side chains of neighboring macromolecules to overlap (Φ<1). In bottlebrush systems, however, the steric repulsion between densely grafted side chains results in chain extension and inhibits side chain interpenetration (Φ≥1).The ratio Ge,gr/Ge,lin≈φ3(1+(Φ/0.7)3) of the plateau modulus of a graft polymer melt, Ge,gr, to that of a linear polymer melt, Ge,lin, is a universal function of the crowding parameter Φ≈φ-1nsc-1/2 and graft polymer composition φ=ng/(ng + nsc), where nsc and ng are the degrees of polymerization of side chains and a spacer separating consecutive side chains along the backbone, respectively. Such universal behavior is verified by poly(n-butyl acrylate) combs and other graft polymers reported in literatures. For graft polymers with entangled side chains, the Ge,gr/Ge,lin ratio is proportional to φ2. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B50.00011: Entanglement in semiflexible polymer melts and solutions from simulations Sai Vineeth Bobbili, Scott Milner The Lin-Noolandi scaling argument predicts the entanglement molecular weight from chain geometry, and is well supported by experimental results for real polymers. The argument assumes that polymers are flexible within their tubes, which fails at some point as chains become stiffer. Everaers has made a different scaling proposal, which crosses over from semiflexible chains to stiff chains as described by Morse. Everaers’ ansatz is consistent with simulation data for a range of bead-spring melts, but is not consistent with LN. In this work, we use MD simulations to explore a wide range of entangled bead-spring ring chains, to find out how entanglement properties vary with chain stiffness and concentration. To topologically equilibrate ring chains, we soften the short-range repulsive potential to allow chains to cross. We calculate entanglement properties using three techniques: chain shrinking to find the primitive path, measuring the tube diameter by the width of the “cloud” of monomer positions about the primitive path, and directly measuring the plateau modulus. As chain stiffness varies, we observe three distinct scaling regimes, suggestive of LN scaling, semiflexible chains, and stiff chains. |
Monday, March 4, 2019 1:51PM - 2:03PM |
B50.00012: Polymer Structures and Their Glass Transition Temperatures: An Intriguing Relationship Tianyu Li, Huiqun Wang, Jimmy W Mays, Kunlun Hong Abstract:Polymer structure play an essential role in dictating chain stiffness and glass transition temperature (Tg). The characteristic ratio (C∞) is an important parameter to describe chain stiffness. In general, polymers with stiffer chains have higher glass transition temperature and correspondingly higher C∞.However, for poly(n-alkyl methacrylates), this is not always true. For example, poly(ethyl methacrylate) has Tg of 65 °C and C∞ of 8.2, but poly(n-hexyl methacrylate) has Tg of -5 °C and C∞ of 11.1. Furthermore, poly(n-alkyl acrylates) generally have lower Tgs than the corresponding poly(n-alkyl methacrylate) but actually have higher C∞values. We believe other structural characteristics, such as stereoisomerism, might play a role in these discrepancies. In this contribution we discuss the intriguing relationships of polymer structure (chain stiffness) and glass transition temperatures with relation to structural parameters and solution properties of well-characterized poly(meth)acrylates. |
Monday, March 4, 2019 2:03PM - 2:15PM |
B50.00013: Electric Field-Induced Critical Point Shift in a Binary Dielectric Polymer Blend Jonathan Martin, Kris T Delaney, Glenn Fredrickson
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