Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session B03: Polymer Nanocomposites: Surfaces and InterfacesFocus Live
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Sponsoring Units: DPOLY DSOFT GSNP Chair: Shiwang Cheng, Michigan State University; Robert Hickey, University of Pennsylvania |
Monday, March 15, 2021 11:30AM - 11:42AM Live |
B03.00001: Theory of segmental relaxation and shear elasticity in polymer nanocomposites Yuxing Zhou, Kenneth Schweizer We recently studied dynamic elasticity in melt polymer nanocomposites (PNCs) using naïve mode coupling theory with structural inputs obtained from PRISM theory (J. Chem. Phys. 153, 114901 (2020)). The glassy shear modulus can be either softened or reinforced by nanoparticle (NP) addition, and connections with the interfacial cohesive energy, a specific measure of free volume, and entropic depletion attractions were established. The same PNC model is now adopted to formulate a theory for the activated segmental relaxation time based on a generalization of the microscopic Elastically Collective Nonlinear Langevin Equation (ECNLE) approach to mixtures that self-consistently captures cooperative activated motion of segments and nanoparticles. A rich dynamical behavior is predicted as a function of particle-segment size ratio, interfacial attraction strength, and NP loading, with both plasticization and anti-plasticization possible. The complexity reflects changes of PNC microstructure with increasing polymer-NP attraction from NP contact clustering, to steric stabilization via adsorbed polymer layers, to polymer-mediated bridging. The key physics relates to the competition between the total PNC density fluctuation amplitude (free volume) and interfacial physical bonding. |
Monday, March 15, 2021 11:42AM - 11:54AM Live |
B03.00002: Molecular Orientation of Phenyl Groups at Graphene/Polystyrene Interface Nityanshu Kumar, Saranshu Singla, Feipeng Yang, Mark Foster, Mesfin Tsige, Ali N Dhinojwala Blending graphene with polymer matrices is of great interest in designing nanocomposites with enhanced thermal and mechanical properties. The challenge is to avoid aggregation of these high surface area graphene sheets. Understanding the molecular interactions between graphene and polymer molecules is important to identify the correct chemistry needed to disperse these nanofillers. Here, we report the use of interface-sensitive sum-frequency generation spectroscopy (SFG), molecular dynamics (MD) simulations, and density functional theory (DFT) to study the orientation of polystyrene chains next to graphene/polystyrene interface. DFT provides information on molecular hyperpolarizability, whereas the MD simulations shed light on the orientation distribution of phenyl and methylene groups. The combination of MD and DFT is used to predict the SFG spectra of PS chains next to a graphene/polystyrene interface. In my presentation, we will compare SFG spectra calculated using MD/DFT with those measured experimentally using SFG. Further, we will discuss the need to independently obtain molecular orientation distributions using MD for correctly analyzing the SFG data. |
Monday, March 15, 2021 11:54AM - 12:06PM Live |
B03.00003: Effect of Chemical Heterogeneity and Architecture of the Interphase on the Rheological Behavior of Polymer Nanocomposites Di Wu, Pinar Akcora Polymer surface-modified nanoparticles have been widely used to tune the mechanical properties of polymer matrices not only because of the improved dispersion state but also the abundant dynamic variation of the polymers in the interfacial region. Our group explores the effect of chemical heterogeneities and varying chain architectures around nanoparticles on tuning the dynamics of particles and interfacial polymers, hence the mechanical properties. Iron oxide (Fe3O4) nanoparticles adsorbed or grafted with poly(methyl methacrylate) (PMMA) chains dispersed in poly(methyl acrylate) (PMA) matrices are prepared and their rheological behavior is characterized. It shows that short adsorbed chains lead to thermal-stiffening, whereas long adsorbed chains yield softening with increasing temperature. A similar trend is found in the systems with larger particle size but with less confined particle diffusion. Conformations and dynamics of adsorbed and grafted chains are discussed to reveal this unusual behavior that relies on interfacial heterogeneities. In addition, other types of adsorbed chains of PA and P2VP, with decreasing rigidity, are compared to understand the role of rigid chains on interfacial dynamics and relaxations. |
Monday, March 15, 2021 12:06PM - 12:18PM Live |
B03.00004: Investigation of polymer behavior confined in the heterogeneous environment using a 2-dimensional model nanocomposite Chen Gong, Donovan Weiblen, Deniz Rende, Di Wu, Pinar Akcora, Rahmi Ozisik Polymer nanocomposites with heterogeneous interfaces in the vicinity of inorganic nanofillers have attracted broad interest due to their functionality. One important finding was that when there exists a large dynamic asymmetry at the interface, nanocomposite may display thermal stiffening. In the current work, a 2-dimensional model nanocomposite is adopted to help understand local thermal properties and dynamics at the heterogeneous interface. The planar model nanocomposite has a sandwich structure, where the top layer is polyethylene oxide (PEO), the middle layer is a high-glass-transition-temperature polymer (such as poly(methyl methacrylate), polycarbonate, poly(2–vinyl pyridine), or polystyrene), and the bottom layer is a silica substrate. Degradation and local glass transition behavior were characterized by Thermogravimetric Analysis (TGA) and Modulated Differential Scanning Calorimetry (MDSC), respectively. Segmental and local relaxation along with cooperativity were characterized by Broadband Dielectric Spectroscopy (BDS). The results affirmed the capability of these techniques in retrieving information from multilayered thin film samples and revealed how polymer chains behave when confined in a heterogeneous environment. |
Monday, March 15, 2021 12:18PM - 12:30PM Live |
B03.00005: Photostability of Organic Glasses under Extreme Nanoconfinement Yueli Chen, Haonan Wang, Ahmad Shamsabadi, Zahra Fakhraai Photodegradation is usually caused by a complex series of chemical reactions initiated by the absorption of ultra-violet light, which drastically reduces effective lifetime of advanced organic functional materials. Previous work has established capillary rise infiltration (CaRI) technique can induce extreme nanoconfinement and significantly affect the properties of materials. |
Monday, March 15, 2021 12:30PM - 1:06PM Live |
B03.00006: The Critical Role of the Interfacial Layer in Polymer Nanocomposites Invited Speaker: Alexei Sokolov In this talk we overview recent studies on structure and dynamics of the interfacial layer in various polymer nanocomposites (PNCs). First we emphasize the difference between the interfacial and rthe bound layer, which are often confused in literature. Then, we employ broad array of experimental techniques and MD-simulations that provide detailed characterization of the interfacial layer. These studies revealed a gradient in the interfacial layer dynamics, but no “glassy” or “dead“ layer. The thickness of the interfacial layer increases upon cooling to Tg, and depends strongly on polymer rigidity, increasing from ~2nm in flexible polymers to ~5 nm in more rigid ones. We discuss a possible connection of the interfacial layer thickness to the dynamic heterogeneity length scale. We emphasize usually overlooked dynamic property of the interfacial layer – strong suppression of the amplitude of structural relaxation on time scale of segmental dynamics. At the end, we present a general picture how microscopic parameters control the interfacial layer, and how by tuning the interfacial layer we can tune macroscopic properties of polymer nanocomposites. |
Monday, March 15, 2021 1:06PM - 1:18PM Live |
B03.00007: Characteristics of the bound polymer layer in polymer nanocomposites Emily Lin, Kaitlin Wang, Amalie Frischknecht, Karen Winey, Robert Riggleman In polymer nanocomposites (PNCs), the dynamics of polymers adjacent to the nanoparticles often greatly impacts the properties, performance, and processability. When polymer-nanoparticle interactions are favorable, a bound layer of polymer forms next to the nanoparticle. In the past decade, significant strides were made to develop our understanding of the polymer dynamics in the bound layer. However, a comprehensive study that examines the effects of nanoparticle size, polymer-nanoparticle interaction, and the solvent quality of the bulk polymer solution on the polymer conformation and adsorption dynamics between the bound layer and the surrounding free polymer chains in solution is still missing. In this study, we used classical density functional theory (DFT) calculations and molecular dynamics (MD) simulations to characterize the effect of polymer-nanoparticle interaction, polymer chain length, and nanoparticle size on the polymer conformation and adsorption thermodynamics and dynamics in the bound polymer layer. We expect that our results will have an important impact on our fundamental understanding of limits of kinetics and thermodynamic dispersion of nanoparticles in PNCs. |
Monday, March 15, 2021 1:18PM - 1:30PM Live |
B03.00008: Molecular Design of Hairy Nanocrystals for Elastomeric Reinforcement Aarushi Srivastava, Yihong Zhao, John Meyerhofer, Li Jia, Mark D. Foster The size of β-sheet nanocrystals self-assembled from β-alanine trimers grafted on polyisobutylene rubber can be controlled and this nanocrystal size affects the morphology of the elastic matrix and thereby the material’s macroscopic elastic properties. The β-sheet crystal size is tailored by altering the density of hydrocarbon chains tethered at the nanocrystal surfaces. Results from TEM, Small Angle X-ray Scattering, and Small Angle Neutron Scattering characterizations of the morphology demonstrate that increasing the density of chain grafting at the crystalline nanodomain surface can sharply limit the nanodomain growth in the direction of hydrogen-bonding in the crystals. The nanocrystal size, in turn, impacts the gradient in chain stretching away from the crystal surface, and the macroscopic volume fraction of unperturbed chains. |
Monday, March 15, 2021 1:30PM - 1:42PM Live |
B03.00009: Modifying the surface properties of polymer films by utilizing polymer/inorganic nanocomposites Spiros Anastasiadis, Fanourios Krasanakis, Thaleia-Michaela Chatzaki, Antigonos Theodorakis, Kiriaki Chrissopoulou Polymer materials with optimized properties can be prepared when nanosized inorganic materials are added to a polymer matrix resulting in a nanocomposite. In this work, we report on the development of superhydrophobic and water repellent polymer nanocomposite coatings deposited on soft polyethylene, PE, substrates by utilizing nanoadditives of different geometries and sizes. The coating morphology and effective roughness were investigated with Scanning Electron Microscopy and profilometry, respectively, as a function of the nanoadditive content. In the case of PE substrates, the optical clarity of the original film was preserved following the nanocomposite coating as verified by UV-Vis spectroscopy. The surface properties of the films were investigated by contact angle measurements; the water contact angle depends strongly on both the polymer and the inorganic nanoadditive utilized for the coating as well as on its composition whereas the contact angle hysteresis was significantly affected by the presence of the inorganic nanoadditives. |
Monday, March 15, 2021 1:42PM - 1:54PM Live |
B03.00010: Polymer/Graphene oxide nanocomposites: Effect of the interfacial interactions on the structure and properties. Fanourios Krasanakis, Ioannis Karnis, Anastassia Rissanou, Konstantinos Karatasos, Kiriaki Chrissopoulou Polymer nanohybrids with enhanced properties can be developed via the addition of nanosized additives to the polymer matrix. In this work, nanohybrids of either linear or hyperbranched polymers and graphene oxide (GO) of varying degree of oxidation are developed to investigate the effect of the different hydrophilicity of the filler on the final structure and properties of the nanohybrids. Additives with different degree of oxidation were attained by altering either the reaction time or the amount of the oxidation medium during oxidation of graphite. The obtained GOs were characterized with X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) and were consequently, mixed with poly(ethylene oxide), PEO, or Hyperbranced Polymers (HBPs). A plethora of experimental techniques was utilized to investigate the hybrids structure, morphology as well as their thermal and rheological properties. Molecular Dynamics simulations were utilized to predict and interpret the behavior of both the GO additives and the nanocomposites and to assist in correlating the obtained structure with the observed properties. This research has been co-financed by Greece and EU (POLYGRAPH, MIS: 5050562). |
Monday, March 15, 2021 1:54PM - 2:06PM Live |
B03.00011: Nano-indentation of nanocomposite polyester coatings Suresh Ahuja The analytical models, molecular models and numerical models are reviewed. The aim of this study was to compare and analyze the mechanical response of nano-indentation loading on surfaces and interfaces of polyester films both linear and cross-linked. Reduced modulus and hardness in polyester and polycarbonate show strain softening that is associated polymer chain flexibility. The spatial constraints imposed to the plastic flow of the interface layer by the rigid indenter and substrate surfaces produce a dynamic effect, demonstrated by the loading rate dependence of the deformation response. In nano-indentation of cross-linked polymers, entanglements physical and chemical affect reduced modulus and hardness dependence on strain. Strain softening and strain hardening as well as dynamic frictional response are applied to indented polymer films consisting of surface, intermediate, and interface layers. The improvement of mechanical properties is found to mainly depend on the nature of the filler and the dispersion and interaction with the matrix. Other factors such as shape, dimensions and degree of orientation of the nanofiller, as well as matrix morphology are discussed. |
Monday, March 15, 2021 2:06PM - 2:18PM Live |
B03.00012: Revealing the structures and dynamics of isotactic polypropylene bound to carbon fibers Zhixing Huang, Yohei Nakanishi, Maya Endoh, Kiminori Uchida, Takeshi Yamada, Kazuki Mita, Tad Koga The addition of fillers affects the overall rheological and mechanical properties of polymers mainly due to the creation of the nanometer-size bound polymer layer (BPL) at the filler surface, at which the polymer has a different behavior than in the bulk. In spite of their importance, the development and optimization of the BPL interface is still based on empirical know-how strategies since the actual mechanism of reinforcement at the polymer/filler interface remain unresolved. Here we present the structures and dynamics of the BPL layer formed on carbon fiber (CF) surfaces. CF/isotactic polypropylene (iPP) nanocomposites play an integral role in a number of industrial applications. Based on a solvent-rinsing method, we successfully prepared the BPL on the CF from CF/iPP composites and characterized the in-situ structures and local segment dynamics of the BPL alone using small-angle neutron scattering and neutron backscattering, respectively. In addition, we mimicked the interface using iPP thin films deposited on carbon layer coated planar silicon substrates and the melting behavior of the BPL alone (after the solvent rinsing process) were investigated by using in-situ atomic force microscopy and grazing-incidence X-ray diffraction. |
Monday, March 15, 2021 2:18PM - 2:30PM Live |
B03.00013: Multiple roles of bound polymer chains in rubber reinforcement Tad Koga, Daniel Salatto, Jan-Michael Carrillo, Maya Endoh, Tomomi Masui, Hiroyuki Kishimoto, Takashi Taniguchi, Madhusudan Tyagi, Victoria Sakai, Margarita Kruteva, Dieter Oswald Richter, Michihiro Nagao According to the Energy Technology Perspectives 2017, in 2050 the total number of cars globally will be three times greater than that in 2010. This increase implies that the development of advanced reinforced synthetic elastomers with balanced, superior performance is indispensable to meet the demand due to the dwindling availability of natural resources. To address this issue, we tackle the critical, but unsolved issue in the field: the roles of polymer chains bound to the filler surface in improving mechanical properties. Using a simplified carbon black-filled polybutadiene in conjunction with neutron scattering/spectroscopy techniques and molecular dynamics simulations, we reveal the novel hierarchical structures and dynamics of bound chains. We further demonstrate the mechanism behind the formation of a stable and adhesive polymer-filler interface between the bound chains and free chains in a matrix. The comprehensive understanding derived and validated with the model elastomer will be beneficial for many other polymer nanocomposites. |
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