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Creators/Authors contains: "Xia, Wenjie"

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  1. This study explores the tensile behavior and dynamical heterogeneity of sodium montmorillonite under extreme conditions using molecular dynamics simulations, providing insights to advance the development of clay minerals for engineering applications.

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    Free, publicly-accessible full text available October 10, 2024
  2. By employing coarse-grained (CG) molecular dynamics (MD) simulations, this study aims to investigate the thermomechanical behaviors of graphene-reinforced conjugated polymer nanocomposites at a fundamental molecular level.

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    Free, publicly-accessible full text available November 2, 2024
  3. Free, publicly-accessible full text available September 26, 2024
  4. Abstract

    Wearable devices benefit from the use of stretchable conjugated polymers (CPs). Traditionally, the design of stretchable CPs is based on the assumption that a low elastic modulus (E) is crucial for achieving high stretchability. However, this research, which analyzes the mechanical properties of 65 CP thin films, challenges this notion. It is discovered that softness alone does not determine stretchability; rather, it is the degree of entanglement that is critical. This means that rigid CPs can also exhibit high stretchability, contradicting conventional wisdom. To inverstigate further, the mechanical behavior, electrical properties, and deformation mechanism of two model CPs: a glassy poly(3‐butylthiophene‐2,5‐diyl) (P3BT) with anEof 2.2 GPa and a viscoelastic poly(3‐octylthiophene‐2,5‐diyl) (P3OT) with anEof 86 MPa, are studied. Ex situ transmission X‐ray scattering and polarized UV–vis spectroscopy revealed that only the initial strain (i.e., <20%) exhibits different chain alignment mechanisms between two polymers, while both rigid and soft P3ATs showed similarly behavior at larger strains. By challenging the conventional design metric of lowEfor high stretchability and highlighting the importance of entanglement, it is hoped to broaden the range of CPs available for use in wearable devices.

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    Free, publicly-accessible full text available December 1, 2024
  5. This study employs all-atomistic (AA) molecular dynamics (MD) simulations to investigate the crystallization and melting behavior of polar and nonpolar polymer chains on monolayers of graphene and graphene oxide (GO). Polyvinyl alcohol (PVA) and polyethylene (PE) are used as representative polar and nonpolar polymers, respectively. A modified order parameter is introduced to quantify the degree of two-dimensional (2D) crystallization of polymer chains. Our results show that PVA and PE chains exhibit significantly different crystallization behavior. PVA chains tend to form a more rounded, denser, and folded-stemmed lamellar structure, while PE chains tend to form an elongated straight pattern. The presence of oxidation groups on the GO substrate reduces the crystallinity of both PVA and PE chains, which is derived from the analysis of modified order parameter. Meanwhile, the crystallization patterns of polymer chains are influenced by the percentage, chemical components, and distribution of the oxidation groups. In addition, our study reveals that 2D crystalized polymer chains exhibit different melting behavior depending on their polarity. PVA chains exhibit a more molecular weight-dependent melting temperature than PE chains, which have a lower melting temperature and are relatively insensitive to molecular weight. These findings highlight the critical role of substrate and chain polarity in the crystallization and melting of polymer chains. Overall, our study provides valuable insights into the design of graphene-based polymer heterostructures and composites with tailored properties. 
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    Free, publicly-accessible full text available July 27, 2024
  6. Free, publicly-accessible full text available May 1, 2024
  7. The fracture mechanics of cellulose nanocrystal (CNC) thin films are strongly dependent on their alignment direction relative to the loading direction.

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  8. Abstract Highlights

    CG modeling is performed to explore the thermomechanical behavior of PCN.

    Effects of nanoclay weight percentage and size on modulus are studied.

    Interface leads to nanoconfinement effect onTgand molecular stiffness.

    Correlations between molecular stiffness and modulus are identified.

    Simulations show spatial variation of dynamical heterogeneity.

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