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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. 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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3. Leveraging peptide–cellulose interactions to tailor the hierarchy and mechanics of peptide–polymer hybrids

   https://doi.org/10.1039/D3TB00079F  

   Jang, Daseul; Beckett, Laura E.; Keum, Jong; Korley, LaShanda T.J. (June 2023, Journal of Materials Chemistry B)

   Inspired by spider silk's hierarchical diversity, we leveraged peptide motifs with the capability to tune structural arrangement for controlling the mechanical properties of a conventional polymer framework. The addition of nanofiller with hydrogen bonding sites was used as another pathway towards hierarchical tuning via matrix–filler interactions. Specifically, peptide–polyurea hybrids (PPUs) were combined with cellulose nanocrystals (CNCs) to develop mechanically-tunable nanocomposites via tailored matrix–filler interactions (or peptide–cellulose interactions). In this material platform, we explored the effect of these matrix–filler interactions on the secondary structure, hierarchical ordering, and mechanical properties of the peptide hybrid nanocomposites. Interactions between the peptide matrix and CNCs occur in all of the PPU/CNC nanocomposites, preventing α-helical ordering, but promoting inter-molecular hydrogen bonded β-sheet formation. Depending on peptide and CNC content, the Young's modulus varies from 10 to 150 MPa. Unlike conventional cellulose-reinforced polymer nanocomposites, the mechanical properties of these composite materials are dictated by a balance of CNC reinforcement, peptidic ordering, and microphase-separated morphology. This research highlights that leveraging peptide–cellulose interactions is a strategy to create materials with targeted mechanical properties for a specific application using a limited selection of building blocks. 

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4. Ordered polymer composite materials: challenges and opportunities

   https://doi.org/10.1039/D0NR07547G  

   Wang, Yuping; Desroches, Griffen J.; Macfarlane, Robert J. (January 2021, Nanoscale)

   null (Ed.)

   Polymer nanocomposites containing nanoscale fillers are an important class of materials due to their ability to access a wide variety of properties as a function of their composition. In order to take full advantage of these properties, it is critical to control the distribution of nanofillers within the parent polymer matrix, as this structural organization affects how the two constituent components interact with one another. In particular, new methods for generating ordered arrays of nanofillers represent a key underexplored research area, as emergent properties arising from nanoscale ordering can be used to introduce novel functionality currently inaccessible in random composites. The knowledge gained from developing such methods will provide important insight into the thermodynamics and kinetics associated with nanomaterial and polymer assembly. These insights will not only benefit researchers working on new composite materials, but will also deepen our understanding of soft matter systems in general. In this review, we summarize contemporary research efforts in manipulating nanofiller organization in polymer nanocomposites and highlight future challenges and opportunities for constructing ordered nanocomposite materials. 

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5. Multifunctional Graphene–Polymer Nanocomposite Sensors Formed by One-Step In Situ Shear Exfoliation of Graphite

   https://doi.org/10.3390/jcs7080309  

   Ashraf, Ali; Chang, Elizabeth; Rahman, Md Ashiqur; Ghosh, Dipannita; Islam, Nazmul; Lynch-Branzoi, Jennifer K. (August 2023, Journal of Composites Science)

   Graphene nanocomposites are a promising class of advanced materials for sensing applications; yet, their commercialization is hindered due to impurity incorporation during fabrication and high costs. The aim of this work is to prepare graphene–polysulfone (G−PSU) and graphene–polyvinylidene fluoride (G−PVDF) nanocomposites that perform as multifunctional sensors and are formed using a one-step, in situ exfoliation process whereby graphite is exfoliated into graphene nanoflakes (GNFs) directly within the polymer. This low-cost method creates a nanocomposite while avoiding impurity exposure since the raw materials used in the in situ shear exfoliation process are graphite and polymers. The morphology, structure, thermal properties, and flexural properties were determined for G−PSU and G−PVDF nanocomposites, as well as the electromechanical sensor capability during cyclic flexural loading, temperature sensor testing while heating and cooling, and electrochemical sensor capability to detect dopamine while sensing data wirelessly. G−PSU and G−PVDF nanocomposites show superior mechanical characteristics (gauge factor around 27 and significantly enhanced modulus), thermal characteristics (stability up to 500 °C and 170 °C for G−PSU and G−PVDF, respectively), electrical characteristics (0.1 S/m and 1 S/m conductivity for G−PSU and G−PVDF, respectively), and distinguished resonant peaks for wireless sensing (~212 MHz and ~429 MHz). These uniquely formed G−PMC nanocomposites are promising candidates as strain sensors for structural health monitoring, as temperature sensors for use in automobiles and aerospace applications, and as electrochemical sensors for health care and disease diagnostics. 

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