Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C54: Smart and Responsive Polymers and Soft Materials II: Molecular Length Scale PhenomenaFocus
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Sponsoring Units: DPOLY GSOFT DBIO Chair: Matthew Green, Arizona State University Room: BCEC 254A |
Monday, March 4, 2019 2:30PM - 2:42PM |
C54.00001: Mechanophore activation in a crosslinked polymer matrix via instrumented indentation Chelsea Davis, Mitchell L Rencheck, Jeremiah Woodcock, Muzhou Wang, Ryan Beams, Stephan Stranick, Aaron Forster, Jefrey Gilman Scratches in transparent polymer coating and barrier layers can cause a host of problems, impacting optical (haze, light transmission, etc.) and mechanical properties (permeability, structural integrity, etc.) The primary focus of this project is to investigate the mechanical activation of a mechanophore (MP)-containing transparent polymer coating. Taking advantage of the amine functionality present in a polyetheramine/bisphenol A epoxy network, we have covalently attached a commercially available Rhodamine dye into a transparent, thermoset polymer. Utilizing the scratch profiles available on a typical nanoindenter, the load was varied so that a transition between ductile (plastic) to brittle deformation was observed within a single scratch. Subsequent fluorescence imaging of the MP-epoxy surfaces revealed the extent of fluorescence activation induced by the mechanical deformation. It has been shown that the Rhodamine-based mechanophore can be used to identify brittle fracture and local stress concentrations prior to macroscopic failure. Fluorescence lifetime and hyperspectral imaging of damage zones provide additional insight into the local deformation around each scratch. |
(Author Not Attending)
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C54.00002: Tryptophan based co-polymer as Fluorescence Turn-Off sensor for explosive detection Vishal Kumar, Soumitra Satapathi The highly sensitive and reliable detection of explosives is of paramount importance for civilian and military security.1,2 |
Monday, March 4, 2019 2:54PM - 3:06PM |
C54.00003: Tough and Photoluminescent Diblock Copolymer Elastomers via Lanthanide Coordination Feng Jiang, Xin Zhang, Doug Henderson, Wonseok Hwang, Robert M Briber, Howard Wang Thermoplastic elastomers (TPEs) of poly(methyl methacrylate)-block-poly(n-butyl acrylate-co-vinyl imidazole) (PMMA-b-P(BA-co-VI)) diblock copolymers have been synthesized as a model system to demonstrate supramolecular photoluminescence (PL) TPEs via lanthanide coordination. Europium ion (Eu3+) with a red PL and terbium ion (Tb3+) with a green PL have been selected as the lanthanide ions to coordinate the imidazole groups of the soft block. Upon microphase separation, hard PMMA blocks form spherical domains in the continuous matrices of the soft P(BA-co-VI) phase. At a volume fraction of 0.29, PMMA hard sphere domains act as a physical network in the matrix. Upon incorporating lanthanide ions, the soft P(BA-co-VI) matrix is cross-linked through metal coordination to form a second physical network. Synergistic interaction and reinforcement of local segmental coordination network and global glassy particle percolation network greatly enhance both the tensile strength and toughness of TPEs without compromising the stretchability. Moreover, the PL spectrum of TPEs can be continuously tuned by varying the composition and molar ratio of Eu3+/Tb3+. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C54.00004: Temperature and pH Dual-Responsive Shape-Transforming Block Copolymer Particles with Tunable Optical Property Junhyuk Lee, Bumjoon Kim We report a simple and robust strategy to prepare temperature/pH dual-responsive shape-switchable block copolymer (BCP) particles composed of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and temperature/pH-responsive poly(N-(2-(diethylamino)ethyl)acrylamide-r-N-isopropylacrylamide) (poly(DEAEAM-r-NIPAM)) surfactants. The polymer surfactants were carefully designed to produce a dramatic change in relative solubility in response to subtle temperature and pH change near physiological condition (i.e. human body temperature and neutral pH). The shape transition of BCP particles from lens to football shape was occurred within very narrow temperature and pH range: no transition for pH 6.0, 40-50 °C for pH 6.5, and 25-35 °C for pH 7.0. Furthermore, the BCP particles showed reversible shape-transforming behavior in response to orthogonal temperature/pH changes. In addition, the incorporation of fluorescent dye-functionalized PS and P4VP into BCP particles allowed colorimetric monitoring of temperature and pH changes, which suggests a promising possibility of these particles in clinical and biomedical application. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C54.00005: Effect of calcium ions on the interactions of end-tethered weak polyelectrolytes Rikkert Nap, Igal G Szleifer We use a molecular model, which combines theory with Monte Carlo and Molecular Dynamics simulations, to study the effect of divalent calcium ions on the interactions on the interactions between two planar surfaces end-tethered with poly(acrylic acid))(PAA). Polyelectrolyte-coated colloids and nanoparticles have nanotechnological and biomedical applications such as sensing and imaging. The addition of calcium ions to monovalent electrolyte solutions leads to a dramatic reduction in the size and range of effective interactions between the two polymer layers. This is caused by the formation of favorable calcium bridges that reduce the effective charge of the polymer layers and, at sufficiently high calcium ion concentrations, can cause the polymer layers to collapse. At physiological conditions and calcium ion concentrations above approximately 1mM, the repulsions between the opposing end-grafted surfaces disappear and attractions occur, accompanied by large structural changes of the opposing layers. These attractions are correlated with the occurrence of interlayer divalent calcium bridges and do not occur for PAA layers in contact with reservoir solutions containing only monovalent ions. Finally, the potential for microphase separation within the PAA layer is explored. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C54.00006: In situ regeneration of oil absorbent via wettability switch of conjugated polymer surfaces Jian Xu, Wei Xu, Yinlun Yuan, Guohao Gao, Eui-Hyeok Yang Absorbent-based technology shows the possibility of full removal and reclaim of oils from water while bringing little adverse effects to the environment. In spite of their promises, the recycle and regeneration of saturated absorbents have been less-explored. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C54.00007: Design principle of multi-responsive smart copolymers Carlos M Marques, Debashish Mukherji, Kurt Kremer Design of multi-responsive smart, soft materials is at the onset of many developments in polymer physics, chemical physics, biophysics and biochemistry research. A system is known as smart responsive when a slight change in external stimuli can drastically alter its structure, function and stability. Furthermore, when the relevant energy scale is of the order of thermal energy, materials are classified as soft matter and are driven by large conformational/compositional fluctuations. At the same time it is very difficult to address these problems in both experimental and theoretical setups. In this work, combining molecular simulation and experiments, we propose design principles of a wide range of smart copolymer architectures in aqueous and mixed solvent environments. This provides an almost predictable conformational behavior and thus presents a highly tunable smart polymer design principle. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C54.00008: Controlling Swelling Behavior of Upper Critical Solution Temperature Micelle Containing Layer-by-Layer Films Victoria Albright, Aliaksei Aliakseyeu, Viktor Selin, John F Ankner, Svetlana A Sukhishvili We explore the role of binding partner strength on temperature-responsive swelling profiles of hydrogen-bonded layer-by-layer (LbL) films containing upper critical solution temperature micelles (UCSTM) composed of poly(acrylamide-co-acrylonitrile)-block-polyvinylpyrrolidone. LbL films were constructed at acidic pH, at temperatures below the UCST, using poly(methacrylic acid) (PMAA) and the PVPON corona of the UCSTM. By using isothermal microcalorimetry, the interaction between PMAA and PVPON in solution was found to be pH dependent and entropically driven at pH 4. The internal structure of UCSTM LbL films deposited at various pHs was monitored with neutron reflectometry using deuterated PMAA to highlight film stratification, while growth and temperature-responsive swelling profiles of multilayers were studied with spectroscopic ellipsometry. Films assembled at higher pH, featuring more ionized PMAA chains, were less well stratified and displayed larger amplitude temperature-triggered swelling changes than those assembled at lower pH. Using pH to control film stratification and functionality can potentially be used in other hydrogen-bonding polymer assemblies. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C54.00009: Mobility and self-healing in star-polymer vitrimers Simone Ciarella, Wouter Ellenbroek Vitrimers are a rapidly developing class of polymeric materials that combine the strength and resilience of covalently crosslinked elastomers with the malleability of thermoplastics. They owe this remarkable feature to a chemical bond-swap mechanism that allows the polymer network to rearrange its architecture without ever being fully disconnected. We simulate this swap mechanism in molecular dynamics simulations of star polymer networks using a 3-body potential-based method we recently developed [1]. We find that the swapping allows the star polymers to diffuse through the material, even on timescales below the stress relaxation time. This provides a mechanism for self-adhesion and self-healing of fully annealed (non-freshly cut) vitrimer surfaces, highlighting their use as durable structural materials. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C54.00010: Molecular Design of Precise Network Polymerized Ionic Liquids for Improved Understanding of Soft Actuators Christopher Evans, Chengtian Shen, Qiujie Zhao Crosslinked network polymerized ionic liquids (n-PILs), with tethered imidazolium cations and mobile bis(trifluoromethane sulfonimide) (TFSI) anions, were investigated as dopant-free (no water or free ionic liquid) soft actuators by sandwiching between flexible electrodes and applying 3V, either AC or DC. These networks are made via a modular synthetic route such that they have tunable polarity and modulus through the choice of either hydrocarbon (HC) or ethylene oxide (EO) monomers and crosslinking density. The Tg is not substantially affected, and the role of conductivity, crosslinking, and modulus can be probed to understand how they systematically affect actuation. Under DC conditions, where conductivity is not a factor, the lower modulus (E) allows for greater bending strain with a non-linear 1/E relation. Under 0.1 Hz AC potentials, the conductivity is important and couples with modulus to affect beam displacement. The choice of EO monomers and low crosslink density lead to the best performance due to high conductivity and low modulus. Because the n-PILs are hydrophobic (< 1 wt% water uptake under ambient conditions), they can be operated over a thousand cycles at 3 V with minimal degradation of performance, as leaching of ionic liquids or water splitting are not an issue. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C54.00011: Chemically Actuated Liquid Crystal-Based Polymer Printer Young Ki Kim, Daniel B. Wright, Pranati Mondkar, Nathan C. Gianneschi, Nicholas L. Abbott Liquid crystals (LC) exhibit the mobility of liquids and long-range order of crystals, leading to anisotropic viscoelastic properties. These properties have been used to design responsive soft materials that can amplify a range of chemical/physical stimuli into macroscopic optical outputs. Recently, we have reported a new class of LC materials based on micrometer-sized aqueous droplets dispersed in thermotropic LCs that both optically report targeted stimuli and trigger release of microcargo initially sequestered within the LC. In this presentation, we will show that these LC materials can be programmed to print three-dimensional polymeric networks and assemblies with diverse sizes and morphologies (from nanometer to millimeter) via triggered polymerization. Specifically, we will demonstrate that it is possible to trigger the polymerization of hydrogels or amphiphilic polymers by hosting initiators within microcargo sequestered in LCs. This work illustrates how it is possible to exploit the elasticity of LCs in combination with polymerization processes to achieve multi-scale responses to molecular-level triggering events. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C54.00012: THz Vibrations of Metal-Organic Frameworks: Thermal and Mechanical Stability Matthew Ryder Neutron scattering is a critical technique in understanding how materials behave at the molecular-level. High-resolution inelastic neutron scattering (INS) in conjunction with density functional theory (DFT) was used to study the lattice dynamics of framework materials and revealed a diversity of valuable information relating to the structural flexibility and was able to explain the origins of anomalous elastic phenomena. Intriguing vibrational motions identified the presence of gate-opening and breathing in zeolitic imidazolate frameworks (ZIFs), and ‘trampoline-like’ mechanisms and molecular rotors reminiscent of negative thermal expansion (NTE) in the MIL-140 series and HKUST-1. However, to fully understand how these promising next-generation materials behave in real-life conditions the thermal and pressure response must be carefully studied. The effect of external stimuli (pressure and temperature) can also reveal the nature and underlying mechanisms behind stimuli-induced phase changes and amorphization. Preliminary results obtained using the one-of-a-kind Spallation Neutron Source (SNS) facility at Oak Ridge National Laboratory (ORNL) indicate elevated levels of anisotropic thermal expansion present in a topical series of framework materials known as MOF 74-M. |
Monday, March 4, 2019 4:54PM - 5:30PM |
C54.00013: Smart and responsive flexible foams via 3D printing of polymer composites Invited Speaker: Emily Pentzer We will report lightweight, highly-compressible, and piezoresistive polymer composite foam structure successfully prepared by 3D printing a thixotropic ink. The structures have exhibits tailorable mechanical strength, high compressibility and remarkable robustness. Inks are composed of nanoclay and carbon black particles in an organic solution polyurethane, and are processed using direct ink writing (DIW) into wearable strain sensor devices. Removal of the clay by chemical etching yields structures with high porosity and good elasticity, which have good compressibility and stable piezoresistive sensing signals at a strain of > 90%. We illustrate these structures can be used in pressure sensing, as well as the sensing of volatile organic solvents. The conductive structures can easily be reprocessed to different shapes and have great potential for lightweight, energy-saving, flexible, highly sensitive, and stable piezoresistive sensors. |
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