Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P33: Hierarchical Structural Emergence in Elastomer Nanocomposites: Dispersion, Dynamics, Structure, Modeling, and Simulation IIFocus
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Sponsoring Units: DPOLY DSOFT Chair: Greg Beaucage, Univ of Cincinnati Room: 505 |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P33.00001: WITHDRAWN ABSTRACT
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Wednesday, March 4, 2020 2:42PM - 2:54PM |
P33.00002: Quantification of dispersion for weakly and strongly correlated fillers in polymer nanocomposites Alex M McGlasson, Kabir Rishi, Greg Beaucage, Michael Chauby, Vikram Kuppa The dispersion of nanoparticles in viscous polymers is dictated by kinetics; interaction potentials between particles; and interfacial compatibility between the matrix and dispersed phases. An analogy has been made between thermally dispersed colloids and kinetically dispersed nanoparticles for cases where only weak interactions exist between particles allowing for a mean field description under the Ginzburg criterion such as for carbon black dispersed in polybutadiene. For these cases the pseudo- second virial coefficient can be used to quantify the quality of dispersion. However, this approach fails for nanoparticles with surface charges or other specific interactions that display strong correlations such as precipitated silica in styrene-butadiene rubber. Here, these strongly correlated systems are investigated in the context of the mean-field systems in order to gain a comparative description of dispersion using the network mesh size and a derived virial coefficient. In the proposed approach, the correlations in nanoaggregates are described by a combined semi-empirical function based on the Born-Green theory and a distribution function that accounts for the non-uniform accumulated strain in nanocomposites. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P33.00003: Recent Study of Small-Angle Neutron Scattering Spectrometer Suanni on Elastomer Nanocomposites Yue Shui, Lizhao Huang, Tingting Wang, Guangai Sun, Jian Gong, Jie Chen, Dong Liu The small-angle neutron scattering (SANS) spectrometer Suanni at CMRR has been brought into operation since 2014 [1]. The SANS-Suanni can achieve a maximum-q up to 10.5 nm-1. In this report, we will discuss some applications on the polymeric materials. By combining extensional rheological and in situ SANS techniques, the correlation between chain deformation and morphology of flow-induced crystallization has been studied [2]. The structure decomposition of silica-filled silicone rubber via the contrast variation SANS technique was presented. SANS results suggested unambiguously the existence of a bound rubber layer with thickness of ca. 8.5 nm [3]. Recently, the correlation between macroscopic mechanical properties and microscopic structures of an optimized silica fraction in silicone rubber was investigated. An optimum filler fraction ranges from 40~50 phr was found, in which the best performances of reinforcement and themorpholog were shown. [4]. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P33.00004: WITHDRAWN ABSTRACT
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Wednesday, March 4, 2020 3:18PM - 3:30PM |
P33.00005: Effect of Initial Dispersion State on the Structure and Property of Polymer Nanocomposites Ga Young Kim, So Youn Y Kim In the colloids-polymer mixture system, the microstructure of particles and polymers are strongly dependent upon their interactions, which can vary systemically with the component concentrations. When the colloidal system is concentrated by solvent evaporation with drying, the continuous change of component concentrations also causes a continuous change in the interparticle interaction. Previous studies have been conducted to control the rate of evaporation or drying conditions of the system. In this study, we show how the initial dispersion of the colloidal system can influence the final structure and property of the polymer nanocomposites. To vary the initial dispersion state, we first set different initial dispersion concentrations to find the effect of polymer and particle volume fractions on the interaction. Second, we provide different equilibrium time for particles to be aggregated. Ensemble- averaged microstructures were analyzed by SAXS measurement and rheological properties were analyzed by rheometer. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P33.00006: Thermodynamic model for dispersion in nanocomposites. Greg Beaucage, Karsten Vogtt, Kabir Rishi, Hanqiu Jiang, Andrew Mulderig Dispersion of nanoparticles can involve thermally driven diffusion of particles or kinetically driven mixing. On the nano- to colloidal scale a virial expansion of osmotic pressure can be used to quantify dispersion. Scattering can be used to measure the osmotic compressibility associated with concentration fluctuations which are related to the second virial coefficient. These fluctuations might be created thermally or by kinetic mixing. For multi-hierarchical materials such as aggregates which cluster to form a macroscopic network, each level of structure contributes to the free energy. This can be quantified in terms of the total number of free particles contributed by each of the levels of structure. For different levels in a hierarchy the energy of aggregation can be associated with an aggregation equilibrium or an apparent equilibrium. The resulting number of particles can be related to the energy of aggregation. This approach is demonstrated for three systems, pigments dispersed with nonionic surfactants; worm-like micelles; and condensation polymerization. |
Wednesday, March 4, 2020 3:42PM - 4:18PM |
P33.00007: Scattering Studies on Hierarchically Self-Organized Filler Particles in Polymers Invited Speaker: Mikihito Takenaka In this study, we investigated the self-organization of nanoparticles dispersed in polymer melts under applied mechanical energy imposed to mixtures that are composed of a bulk of the particle powder and a bulk of the polymer melt. Using various scattering methods that enable the exploration of structures that exist over a length scale that spans from ~0.1 nm to ~20 mm, we elucidated that the self-organized particles had hierarchical structures with various hierarchical levels as follows: primary particles (PPs), aggregates of the PPs fused together, clusters of the aggregates, and partially interdigitating mass-fractal structures built up by the clusters. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P33.00008: First principles Study of Interaction of Polymer Molecules with Flat Carbon Nanotubes Geeta Sachdeva, Ravindra Pandey, Gregory M. Odegard Polymer composites possess an integrated combination of structures and properties associated with the host matrix and fiber material (e.g. carbon nanotubes), and thus holding the potential as high strength materials. In general, the load transfer from the matrix to the fiber depends upon the strength of bonding at the interface which characterizes the mechanical strength. In this talk, we present the results based on density functional theory for the composite consisted of epoxy/BMI resins and flat carbon nanotubes with an aim to provide atomistic description of the interface which determines the mechanical strength of the polymer composite. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P33.00009: Multiscale Modeling of Fracture in Epoxy/CNT Nanocomposites Hayden Hollenbeck, Chengyuan Wen, Ralph Romero, Tabassum Ahmed, Neslihan Genckal, Nishant Shirodkar, Gary Seidel, Shengfeng Cheng Modeling fracture in a polymer nanocomposite with molecular resolution is a big challenge. We have developed a multiscale modeling framework on the basis of coarse-grained molecular dynamics (CG-MD) simulations and peridynamics to study fracture initiation and propagation in epoxy/CNT nanocomposites. The CG model constructed via a hierarchical coarse-graining scheme enables us to model an epoxy network at micrometer scale and still capture its mechanical properties including various moduli. A jointed-tube model is developed for CNTs that overcomes the corrugation issue in traditional CG potentials between CNTs and polymers. Peridynamics simulations of CG CNT bundles dispersed in CG epoxy are used at the microscale to generate statistical distributions of moduli and fracture properties to be used in macroscale peridynamics simulations of fracture toughness tests. The calculations are validated against physical experiments at a given macroscale volume fraction. Successful validation of our hybrid hierarchical-concurrent modeling framework integrating CG-MD and peridynamics models paves the way to designing epoxy/CNT nanocomposites with desired fracture properties via tuning CNT loading and dispersion state. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P33.00010: Molecular Dynamics Investigation of the Structural and Mechanical Properties of Off-Stoichiometric Epoxy Resins Chang Woon Jang, John Lawson We carried out molecular dynamics (MD) simulations to measure the mechanical properties of various off-stoichiometric polymers regarding amine to epoxy ratios (r) and to understand the stiffness of the polymers in terms of their structures. The aerospace-grade API-60 epoxy resin is used as an adhesive bond for assembling large-scale composite structures via the co-curing-ply bonding method. This method will produce a reliable and certifiable composite joint without additional fasteners. Calculated Young’s modulus was measured from the uniaxial tension simulation with several high strain rates, and the experimental modulus was estimated by extrapolating the simulation results. We found that the stiffness was associated with molecular packing caused by chemical cross-linking. We also found that the number of network clusters gradually decreased as the ratio approached r = 1.0, which made the tighter cluster and the system much stiffer with an increase in the molecular weight and the degree of cross-linking. Structural properties such as Rg, MSD were measured to figure out the degree of stiffness with respect to the r. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P33.00011: Deformation of Epoxy Nano-Composites Suresh Ahuja Polymeric materials show properties which come from the interplay of phenomena at various length and time scales. The presence of layered silicates in polymers (PNC) changes the viscoelastic behavior of the unfilled matrix from liquid-like to solid-like because of the formation of a three-dimensional percolating network of exfoliated or intercalated stacks. This gel-like behavior is a direct consequence of the highly anisotropic nature of the nano-clays which prevents their free rotation and the dissipation of stress. Particle to particle interactions is the dominant mechanism in fumed silica nanocomposites whereas particle to polymer interaction is the dominant one in colloidal silica nanocomposites at identical filler concentrations. |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P33.00012: Effect of interface modifiers on the cure, mechanical and viscoelastic properties of hierarchical carbon nanotube composites. Ajay Krishnamurthy, Ran Tao, Qi An, Aaron M Forster Addition of carbon nanotubes (CNTs) to traditional fiber-reinforced polymer composites (FRPs) has led to significant improvements in multifunctional capabilities of these materials. However, achieving these superior properties require incorporating relatively large CNT mass fractions (greater than 1%) where methods of dispersing CNTs in polymer matrix fail. Directly grafting CNTs onto fiber surfaces prior to resin infusion is a viable alternative and here this is achieved by using an electrophoretic deposition (EPD) process. To deposit the CNTs on fiber surfaces, they are first oxidized and mixed with a polyelectrolyte (such as polyethyleneimine (PEI)) which upon protonation is used to drive the CNTs onto fiber surfaces. In our previous study, we observed that the presence of small percentages of PEI affects the viscoelastic properties and the hydrogen dynamics of the composite. Here we aim to isolate the effect of PEI in the absence of CNTs and glass fibers and study its effect on the cure kinetics, mechanical properties and viscoelastic characteristics of the resin system. The cure process is understood using differential scanning calorimetry, the viscoelastic characteristics using dynamic mechanical thermal analysis and the mechanical properties using tensile testing. |
Wednesday, March 4, 2020 5:18PM - 5:30PM |
P33.00013: Adhesion Strength of Block Copolymer Modified Epoxy Adhesives Vincent Pang, Zachary John Thompson, Guy D. Joly, Frank S Bates, Lorraine F. Francis Epoxies are widely used as coatings and structural adhesives in the aerospace, automotive, and consumer goods industries. Prior studies have shown that the addition of block copolymers (BCPs) to epoxy resins can increase bulk fracture toughness, but little work has been done to understand the adhesive properties of these modified epoxy systems. In this work, the influence of self-assembled BCP nanostructures on the adhesion strength of epoxy thermosets was evaluated. Poly(ethylene-alt-propylene)-b-poly(ethylene oxide) BCP modifiers of various molecular weights and weight fractions were mixed into an epoxy resin, forming well dispersed nanoscale structures. Two self-assembled morphologies were studied: spherical micelles and bilayer vesicles. For both nanostructure morphologies, the modified epoxies exhibited significant improvements in bulk fracture toughness, with no reduction in elastic modulus. Single-lap-joint shear tests showed a significant (~50%) increase in the adhesion strength when spherical micelle modified epoxies were used on surface roughened aluminum. In contrast, vesicle-forming modifiers were detrimental, with a 36% reduction in adhesion strength. Possible mechanisms for the adhesion strength results will be discussed. |
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