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1. PRECISE 3D STRUCTURING OF POLYMER NANOCOMPOSITES USING TRIAXIAL MAGNETIC FIELDS

   Atescan, Yagmur; Yamamoto, Namiko. (January 2019, Composites)

   Polymer nanocomposites have been sought after for their light weight, high performance (strength-to-mass ratio, renewability, etc.), and multi-functionality (actuation, sensing, protection against lightning strikes, etc.). Nano-/micro-engineering has achieved such advanced properties by controlling crystallinity, phases, and interfaces/interphases; hierarchical structuring, often bio-inspired, has been also implemented. While driven by the advanced properties of nanofillers, properties of polymer nanocomposites are critically affected by their structuring and interfaces/interphases due to their small size (< ~50 nm) and large surface area per volume. Measures of their property improvement by nanofiller addition are often smaller than theoretically predicted. Currently, application of these novel engineered materials is limited because these materials cannot often be made in large sizes without compromising nano-scale organization, and because their multi-scale structure-property relationships are not well understood. In this work, we study precise and fast nanofiller structuring with non-contact and energy-efficient application of oscillating magnetic fields. Magnetic assembly is a promising, scalable method to deliver bulk amount of nanocomposites while maintaining organized nanofiller structure throughout the composite volume. In the past, we have demonstrated controlled alignment of nanofillers with tunable inter-assembly distances with application of oscillating one-dimentional magnetic fields (~100s of G), by taking advantage of both magnetic attraction and repulsion. The low oscillation frequency (< 1 Hz) was tuned to achieve maghemite nanofiller alignment patterns, in an epoxy matrix, with different amount of inter-nanofiller contacts with the same nanofiller volume fraction (see Figure 1a). This work was recently expanded to three-dimensional assembly using a triaxial Helmholtz coil system (see Figure 1b); the system can apply the triaxial magnetic fields of varying magnitude (max. ±300G, ±250G, ±180G (x-y-z)) and frequency (0 to 1 Hz, ~0.1 Hz resolution) with controlled phase delay to the sample size of 1.5” x 2.5” x 3.5”(x-y-z). Two model systems are currently studied: maghemite nanofillers in an elastomer for magnetoactuation, and nickel-coated CNTs in an thermoset for mehcniacl and transport property reinforcement. The assembled nanofiller structures are currently characterized by microCT; microCT scan data (see Figure 1b) are segmented through a machine learning algorithm, and will be modeled for their transport properties using a Monte Carlo method. These estimated properties will be compared with the experimentally characterized mechanical, transport, and actuation properties, providing the structure-interphase-property relationships. In future, we plan to integrate these nanocomposites to CFRPs for interlaminar property reinforcement, possibly with an out-of-autoclave composite processing. 

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2. Structural Insight in the Interfacial Effect in Ferroelectric Polymer Nanocomposites

   https://doi.org/10.1002/adma.202005431  

   Liu, Yang; Yang, Tiannan; Zhang, Bing; Williams, Teague; Lin, Yen‐Ting; Li, Li; Zhou, Yao; Lu, Wenchang; Kim, Seong_H; Chen, Long‐Qing; et al (November 2020, Advanced Materials)

   Abstract Both experimental results and theoretical models suggest the decisive role of the filler–matrix interfaces on the dielectric, piezoelectric, pyroelectric, and electrocaloric properties of ferroelectric polymer nanocomposites. However, there remains a lack of direct structural evidence to support the so‐called interfacial effect in dielectric nanocomposites. Here, a chemical mapping of the interfacial coupling between the nanofiller and the polymer matrix in ferroelectric polymer nanocomposites by combining atomic force microscopy–infrared spectroscopy (AFM–IR) with first‐principles calculations and phase‐field simulations is provided. The addition of ceramic fillers into a ferroelectric polymer leads to augmentation of the local conformational disorder in the vicinity of the interface, resulting in the local stabilization of the all‐transconformation (i.e., the polar β phase). The formation of highly polar and inhomogeneous interfacial regions, which is further enhanced with a decrease of the filler size, has been identified experimentally and verified by phase‐field simulations and density functional theory (DFT) calculations. This work offers unprecedented structural insights into the configurational disorder‐induced interfacial effect and will enable rational design and molecular engineering of the filler–matrix interfaces of electroactive polymer nanocomposites to boost their collective properties. 

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3. POLYMER INFILTRATED NANOPOROUS GOLD: KINETICS AND OPTICAL PROPERTIES OF NOVEL POLYMER NANOCOMPOSITES

   Kong, Weiwei (December 2024, Scholarly Commons)

   One of the biggest challenges in the field of polymer nanocomposites (PNCs) is to disperse high nanofiller loadings into the polymeric matrix. The high loading and uniform dispersion are limited by the unfavored polymer/nanofiller thermodynamics and the tendency for nanofiller to aggregate. In this thesis, these are circumvented by using nanoporous gold (NPG) as a scaffold for polymers to fill. The ultra-high loading (>50 vol%) is achieved by infiltrating polymer melts into NPG to produce a polymer infiltrated nanoporous gold (PING) composite. This novel composite provides promises for the next generation advanced materials for coating, optical sensors, actuators, and batteries. This thesis contributes to the better understanding of polymer kinetics under moderate confinement by varying the interfacial energy between polymer and pore wall and investigating the temperature dependence of infiltration. Confinement enhances polymer kinetics while decreasing the infiltration time dependence on Mw due to the combined effect of loss in entanglement and adsorbed chain fraction. When polymer and the wall interfacial energy is stronger, a physiosorbed layer forms, resulting in slower kinetics compared to that for weaker interfacial energy. The temperature dependence of the polymer kinetics inside NPG follows the bulk WLF behavior at lower confinement degrees, while the kinetics deviate from the bulk WLF at higher confinement levels due to the decrease in thermal expansion coefficient. Those fundamental studies on polymer kinetics enable the optimization of preparing PING composites for the use of industrial scale applications and encourage additional studies such as ion conductivities of PING. The optical properties study established UV-Vis spectroscopy as a new approach to track polymer kinetics while simultaneously broadening the potential PING applications to optically responsive membranes. This thesis presents a pathway of fabricating PING composite while kinetics studies as well as the optical study enable scientists to better understand polymers behavior under confinement and advance the toolbox for creating interconnected polymer/filler systems at high filler concentrations. 

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4. 2D‐Nanofiller‐Based Polymer Nanocomposites for Capacitive Energy Storage Applications

   https://doi.org/10.1002/smsc.202300016  

   Bera, Sumit; Singh, Maninderjeet; Thantirige, Rukshan; Tiwary, Saurabh Kr; Shook, Brian T.; Nieves, Elianie; Raghavan, Dharmaraj; Karim, Alamgir; Pradhan, Nihar R. (April 2023, Small Science)

   High‐energy‐density storage devices play a major role in modern electronics from traditional lithium‐ion batteries to supercapacitors for a variety of applications from rechargeable devices to advanced military equipment. Despite the mass adoption of polymer capacitors, their application is limited by their low energy densities and low‐temperature tolerance. Polymer nanocomposites based on 2D nanomaterials have superior capacitive energy densities, higher thermal stabilities, and higher mechanical strength as compared to the pristine polymers and nanocomposites based on 0D or 1D nanomaterials, thus making them ideal for high‐energy‐density dielectric energy storage applications. Here, the recent advances in 2D‐nanomaterial‐based nanocomposites and their implications for energy storage applications are reviewed. Nanocomposites based on conducting 2D nanofillers such as graphene, reduced graphene oxide, MXenes, semiconducting 2D nanofillers including transition metal dichalcogenides such as MoS₂, dielectric 2D nanofillers including hBN, Mica, Al₂O₃, TiO₂, Ca₂Nb₃O₁₀and MMT, and their effects on permittivity, dielectric strength, capacitive energy density, efficiency, thermal stability, and the mechanical strength, are discussed. Also, the theory and machine‐learning‐guided design of polymer 2D nanomaterial composites is learnt and the challenges and opportunities for developing ultrahigh‐capacitive‐energy‐density devices based on these nanofiller polymer composites are presented. 

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5. Polymer‐Grafted Nanoparticles as Single‐Component, High Filler Content Composites via Simple Transformative Aging

   https://doi.org/10.1002/adfm.202107139  

   Kubiak, Joshua_M; Macfarlane, Robert_J (October 2021, Advanced Functional Materials)

   Abstract Polymer‐grafted nanoparticles (PGNPs) are ideal additives to enhance the mechanical properties and functionality of a polymer matrix and can even potentially serve as single‐component building blocks for highly filled composites if the polymer content is kept low. The major challenge facing such syntheses is that PGNP‐based solids with short polymer brushes often have low mechanical strength and limited processability. It therefore remains difficult to form robust architectures with a variety of 3D macroscopic shapes from single‐component PGNP composites. Forming covalent bonds between cross‐linkable PGNPs is a promising route for overcoming this limitation in processability and functionality, but cross‐linking strategies often require careful blending of components or slow assembly methods. Here, a transformative aging strategy is presented that uses anhydride cross‐linking to enable facile processing of single‐component PGNP solids via thermoforming into arbitrary shapes. The use of lowT_gpolymer brushes enables the production of macroscopic composites with>30 vol% homogeneously distributed filler, and aging increases stiffness by 1–2 orders of magnitude. This strategy can be adapted to a variety of polymer and nanofiller compositions and is therefore a potentially versatile approach to synthesize nanocomposites that are functional, mechanically robust, and easily processable. 

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