Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L33: Hierarchical Structural Emergence in Elastomer Nanocomposites: Dispersion, Dynamics, Structure, Modeling, and Simulation IFocus
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Sponsoring Units: DPOLY DSOFT Chair: Anne-Caroline Genix, Université de Montpellier Room: 505 |
Wednesday, March 4, 2020 8:00AM - 8:12AM |
L33.00001: Rheological and Electrical Percolation Behavior of Carbon Black Suspendedin Propylene Carbonate Jeffrey Richards, Julie Hipp, Norman J. Wagner In this work, the microstructural origin of the rheo-electric behavior of carbon black gels and suspensions is studied. These materials find widespread use as conductive fillers in composites and slurry-based electrochemical energy storage technologies. In these applications, both the viscosity and electrical conductivity are key design parameters. We use microstructural, rheological and electrical measurements to understand the origin of percolation in these suspensions and rationalize the results using a fluid-cluster-gel transition. The results of these studies explain many emerging observations of the macroscopic behavior of filled carbon black suspensions and guide the way toward improving their rheological and electrical performance. |
Wednesday, March 4, 2020 8:12AM - 8:24AM |
L33.00002: Dielectric & Dynamic response of emergent hierarchical filler networks in polymer nanocomposites Kabir Rishi, Ashish Gogia, Greg Beaucage, Vikram Kuppa, Anh Tang Commercial nanocomposites such as tire compounds are composed of dispersions of carbon black/silica mass fractal aggregates in an elastomer/oil blend, the performance of which is related to the nano-aggregate network structure, the interfacial chemical affinity and extent of dispersion based on accumulated strain. These composites display a complex hierarchical structure intimately tied to their inherent incompatibility and processing history. On the nanoscale carbon black displays primary particles aggregated into mass fractal aggregates that percolate locally above about 5wt.% into a network cluster. In the linear viscoelastic regime, this network dictates the high-frequency response.1 At higher concentrations near 20wt.% the local aggregated clusters agglomerate into a micron-scale mass fractal network associated with electrical conductivity that influence the gel-like dynamic response at low frequencies.2 The impact of the inherent particle structure, the attributes of the nano-scale and meso-scale networks on the dynamic and electrical moduli of these systems was explored using different industrial grade carbon blacks. |
Wednesday, March 4, 2020 8:24AM - 8:36AM |
L33.00003: Rheology and Shear-Induced Structural Evolution in Model Conductive Carbon Black Suspensions Julie Hipp, Jeffrey Richards, Norman J. Wagner Carbon black is commonly used in many technological applications ranging from tire rubbers and inks to electrochemical energy storage devices. In these applications, shear plays an important role in determining end performance due to the shear-induced structural changes and resulting change in properties that occur during mixing, processing, and application steps. To understand this shear-dependent behavior, the microstructure of carbon black suspensions is directly measured by performing Rheo-USANS (Ultra-Small Angle Neutron Scattering) experiments at a range of applied shear rates for suspensions with varying interaction strength, particle loading, and building block characteristics. These experiments show that a dramatic structural transformation from large, dense agglomerates to small, open agglomerates is predictable using the inverse Bingham number, which compares the measured stress to the yield stress of the suspension. Additionally, at high shear rates, the self-similar breakdown of agglomerates is shown to be dependent on the Mason number, which compares shear forces to interparticle attractions. This structural evolution explains many behaviors that are not well understood such as apparent shear-thickening and tunability of yield stress and elasticity. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L33.00004: Polyisoprene silica nanocomposites and its structure property relationship Deboleena Dhara, Andrew Jimenez, Zaid M Abbas, Morton M Denn, Brian C Benicewicz, Sanat Kumar Recently, tire companies have sought to improve their fuel economy to meet the demand for a higher fuel efficiency and environmental sustainability. To achieve this goal, tire technologies have looked to improving the tire rolling resistance. In this talk, we investigate the structure-property relationship of polymer grafted nanoparticles, where the grafted polymer provides a better control over the dispersion of the particles in a polymer matrix. The dispersion and resulting morphologies of various systems were studied and followed by rheology and dynamic mechanical testing to probe the impact of the various structures on the mechanical properties, in the melt and the crosslinked forms. Using small amplitude oscillatory shear, we found that increasing nanoparticle loading significantly contributed to mechanical reinforcement. Reduction in tan delta that accompanies this reinforcement indicates an improvement in rolling resistance. In addition, creep measurements help us to expand the frequency window of our study, allowing access to the lower frequencies that are relevant to the operating frequencies of a tire. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L33.00005: Microscopic Origins of Dynamic Mechanical Properties of Filled Rubber Investigated with X-ray Photon Correlation Spectroscopy Dillon Presto, Suresh Narayanan, Bryce Meyer, John Meyerhofer, Sergio Moctezuma, Mark Sutton, Mark Foster The mechanical properties of nanoparticle filled rubber are largely determined by the structure of the filler network and filler/polymer interactions. These reinforced rubbers have broad commercial utility, such as use in tire tread technology. The dynamic mechanical properties of these systems have a major impact on tire safety and fuel economy. Despite their importance, the connections between microscale filler behavior and macroscale performance are not well understood. Recent developments in X-ray photon correlation spectroscopy (XPCS) allow us to probe the microscale dynamics of filler particle networks and determine how this influences macroscale properties. We have used in-situ XPCS on styrene-butadiene rubber (SBR) filled with silicas of different surface chemistries under dynamic strain to probe the rearrangement of the filler network. We draw connections between the filler/polymer interaction and the resulting network structure, filler dynamics, and macroscopic properties. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L33.00006: Probing dynamics and crosslink morphology of thermosets during cure via XPCS Edward Trigg, Hilmar Koerner Epoxy-based systems have been widely used for decades, from aircraft parts to consumer goods. However, there are still gaps in the fundamental understanding of their crosslinking (curing) behavior, specifically heterogeneities in crosslink topology depending on cure cycle rates. Optimization of cure cycles is key to agile polymer matrix processing in industry and government. Here, we use X-ray photon correlation spectroscopy (XPCS) to study the crosslinking of epoxies in real time, with dilute nanoparticles as tracers to study the effect of the progressing crosslink topology as it confines the dynamics of the tracer. A series of six epoxy systems are presented, wherein the ratio of two curing agents is systematically varied. The fully cured systems range from linear polymers to densely crosslinked resins, enabling a deeper understanding of their cure mechanisms and crosslink topologies. XPCS shows diffusive motion at low degrees of cure, and a sharp transition to ballistic motion at higher cure, which depends on composition. DSC, in situ near-FTIR, and MC simulations complement the XPCS data. XPCS can be used as a tool to interpret crosslinking mechanisms without dynamically perturbing the system as is done in rheology. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L33.00007: Influence of Graft Density on Dynamically Coupled Polymer Grafted Nanocomposites Andrew Ehlers, Pinar Akcora, Rahmi Ozisik The viscoelastic behavior of polymer grafted nanocomposites (PGNs) with significantly different glass transition temperatures (Tgs) between the graft and matrix polymers is investigated with molecular dynamics simulations. These types of PGNs have been shown to have reversible and repeatable stiffening behavior upon heating (Senses, E.; Isherwood, A.; Akcora, P. ACS Appl. Mater. Interfaces 2015, 7, 14682). This unique thermal stiffening behavior was attributed to the dynamic coupling of the high-Tg adsorbed chains and the low-Tg matrix chains. The PGN studied in the current work consists of a nanoparticle with grafted high-Tg polymer chains in a low Tg polymer matrix. The effect of the dynamic coupling of the grafted and matrix polymer chains is studied by molecular dynamics (MD) simulations. Results of MD simulations indicate that grafted chains drastically slow down matrix chain dynamics and also form a percolated network at high nanoparticle concentrations. The influence of the graft density on viscoelastic properties is investigated to identify the mechanism of the observed stiffening in these types of PGNs. |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L33.00008: The emergence of quasi-sinusoidal nonlinearity in particle-filled polymer solutions Wentao Xiong, Xiaorong Wang Systematic rheometric measurements are carried out to explore the nonlinear responses of carbon black-filled polyisoprene/squalene solutions with the polymer concentrations f in the matrix ranging from the coil overlapping state (Φ =Φ*) to the melt state (Φ =1). At the coil overlapping state when Φ <<1, the system shows the classic nonlinearity, where the storage modulus G’ decreases as strain amplitude increases and the resulting stress responses are deviated from sinusoidal waves. At the melting state when Φ = 1, the system displays a new nonlinearity, where the stress responses are surprisingly sinusoidal regardless the reduction of G’. Between the two states when Φ*< Φ <1, the system exhibits a complex nonlinear behavior throughout a wide range of Φ. The ratio of the third to the first harmonics I3/I1 in the stress responses first decreases rapidly reaching a minimum when Φ ≈ 0.1, then increases to a maximum when Φ ≈ 0.3, after which it decreases again as Φ approaches 1. Remarkably, the filler flocculation in the system also displays the corresponding minimum and maximum values. The quasi-sinusoidal response in a system is apparently due to the restoration of broken filler network requiring longer than the time scale of a typical dynamic perturbation. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L33.00009: Single Particle Tracking of Sticky and Non-Sticky Nanoparticles in Polymer Melts Jinseok Park, Eric Bailey, Russell Composto, Karen Winey While nanoparticle (NP) diffusion in polymer melts is important to the fabrication and applications of polymer nanocomposites, the influence of the NP/polymer interaction is poorly understood. Investigation of the weak NP/polymer interactions is experimentally challenging tendency for nanoparticle aggregation. Here, the diffusion coefficients of weakly attracting (methyl capped, CH3 QDs) and strongly attracting (carboxylic acid capped, COOH QDs) nanoparticles (radius ~ 6.5 nm) in poly(propylene glycol) (PPG) melts were measured by single particle tracking (SPT). The mean-squared displacements and van Hove distribution of nanoparticle motion show Brownian motion of non-aggregated nanoparticle, in the long-time diffusion regime (~1s). For weakly interacting CH3 QDs, the effective nanoparticle radius is independent of PPG MW due to the absence of a bound layer. For strongly interacting COOH QDs, the effective radius of the nanoparticle increases with the PPG molecular weight as MW0.5, indicating a long-lived bound layer. By obtaining spatial and temporal diffusion behavior of single nanoparticles, SPT provides previously inaccessible information on the nanoparticle diffusion in polymer melts. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L33.00010: A Coarse Grained Model for the Simulation of dynamic Properties of Filled Elastomers Mariia Viktorova, Reinhard Hentschke, Hossein Ali Karimi-Varzaneh The properties of rubber are strongly influenced by the distribution of filler within the polymer |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L33.00011: The influence of shear rate and adsorbed polymer chain flexibility on thermally stiffening nanocomposites Chen Gong, Pinar Akcora, Rahmi Ozisik The novelty of the nanocomposite used in the current work is that it thermally stiffens with increasing temperature. It consists of a low glass transition temperature (Tg) polymer matrix incorporating silica nanoparticles that contain an adsorbed high-Tg polymer. Although the unique thermal-stiffening property has great application potential, the weak interactions between the adsorbed polymer and nanoparticles make it vulnerable to severe shear stresses that are prevalent in standard processing operations. In the current study, a laboratory mixing extruder was used to process nanocomposites that were initially solution blended, as a function of shear rate and adsorbed polymer chemistry. The extrudates were characterized via multiple methods such as electron microscopy, small angle X-ray scattering, and rheometry. Results indicated that the extrusion process altered the dispersion and distribution of nanoparticles, thereby, leading to changes in the mechanical properties depending on the adsorbed polymer chain flexibility – systems with flexible adsorbed chains recovered most of their mechanical performance. The effect of adsorbed chain flexibility provides an insight into designing thermally stiffening nanocomposites with better processability. |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L33.00012: Understanding the Dispersion and Aggregation of fillers in Polymer Nanocomposites using Dissipative Particle Dynamics (DPD) Simulations of Polymer-Filler Blends Ashish Gogia, Kabir Rishi, Alex M McGlasson, Greg Beaucage, Vikram Kuppa Enhancing the properties of polymeric systems such as natural rubber by the addition of suitable additives provides for interesting applications, both mundane and novel. Such nanocomposites contain nanoscale fillers of varying miscibility, including carbon black, silica, metal oxides, pigments, and/or various combinations thereof. These complex systems exhibit rich phase behavior resulting from thermodynamic interactions and kinetic history. In this research, we perform Dissipative Particle Dynamics (DPD) simulation of polymer chains with aggregated and free filler particles, varying polymer-polymer, filler-filler, and polymer-filler interaction energy, to understand the hierarchical structure and dispersion over multiple length and time-scales. Our results demonstrate the role of concentration, temperature and interaction strength on the clustering of fillers, investigated via their fractal dimension, the radius of gyration, mesh size and population distributions, and are compared with small-angle x-ray scattering data. |
Wednesday, March 4, 2020 10:24AM - 11:00AM |
L33.00013: Polymer – nanocomposites at rest and under deformation: structure of the nanofillers, conformation of the chains, and related mechanical reinforcement. Invited Speaker: François Boué We review work from Laboratory Léon Brillouin and associated groups, on the structure of polymer-nanoparticles composites, under deformation, in relation with mechanical properties improvement of plastics. |
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