Multiscale Polymer Dynamics in Hierarchical Carbon Nanotube Grafted Glass Fiber Reinforced Composites

Recent Progress in Modifications, Properties, and Practical Applications of Glass Fiber

As a new member of the silica-derivative family, modified glass fiber (MGF) has attracted extensive attention because of its excellent properties and potential applications. Surface modification of glass fiber (GF) greatly changes its performance, resulting in a series of changes to its surface structure, wettability, electrical properties, mechanical properties, and stability. This article summarizes the latest research progress in MGF, including the different modification methods, the various properties, and their advanced applications in different fields. Finally, the challenges and possible solutions were provided for future investigations of MGF.

Relative effects of polymer composition and sample preparation on glass dynamics

Modern design of common adhesives, composites and polymeric parts makes use of polymer glasses that are stiff enough to maintain their shape under a high stress while still having a ductile behavior after the yield point. Typically, material compositions are tuned with co-monomers, polymer blends, plasticizers, or other additives to arrive at a tradeoff between the elastic modulus and toughness. In contrast, strong changes to the mechanics of a glass are possible by changing only the molecular packing during vitrification or even deep in the glassy state. For example, physical aging or processing techniques such as physical vapor deposition increase the density, embrittle the material, and increase elastic modulus. Here, we use molecular simulations, validated by positron annihilation lifetime spectroscopy (PALS) and quasi-elastic neutron scattering, to understand the free volume distribution and the resulting dynamics of glassy co-polymers where the composition is systemically varied between polar 5-norbornene-2-methanol (NBOH) and non-polar ethylidene norbornene (ENB) monomers. In these polymer glasses, we analyze the structural features of the unoccupied volume using clustering analysis, where the clustering is parameterized to reproduce experimental measurements of the same features from PALS. Further, we analyze the dynamics, quantified by the Debye-Waller factor, and compare the results with softer, lower density states. Our findings indicate that faster structural relaxations and potentially improved ductility are possible through changes to the geometric structure and fraction of the free volume, and that the resulting changes to the glass dynamics are comparable to large changes in the monomer composition.

Influence of Interfacial Bonding on the Mechanical and Impact Properties Ring-Opening Metathesis Polymer (ROMP) Silica Composites

Polymers formed by ring-opening metathesis polymerization (ROMP) such as poly(dicyclopentadiene) (pDCPD) exhibit a technologically desirable combination of high toughness, high glass transition temperature, and outstanding low-temperature performance. However, because of their nonpolar molecular structure, they tend to suffer from relatively low elastic moduli and poor adhesion to common fillers, fibers, and substrates, limiting their utility as adhesives and composite binders without specialized bonding agents. Here, we investigate the mechanical properties of a pDCPD-based copolymer filled with well-defined spherical microparticles having four distinct surface chemistries capable of strong, moderate, or weak bonding to the matrix with surfaces ranging from polar to nonpolar. Measurements in uniaxial tension, quasi-static fracture, and high-velocity impact are complemented by digital image correlation (DIC), scanning electron microscopy (SEM) fractography, and X-ray computed tomography (X-μCT) of subcritically loaded crack tips, yielding insight into the complex roles played by interfacial bonding in strength, stiffness, and toughening mechanisms of an already tough polymer. Analysis using quantitative fracture and impact mechanism models provided valuable guidelines for designing heterogeneous systems that combine structural and tough performance.

Rapid Nanowelding of Carbon Coatings onto Glass Fibers by Electrothermal Shock

With the rapid development of nanomanufacturing, scaling up of nanomaterials requires advanced manufacturing technology to composite nanomaterials with disparate materials (ceramics, metals, and polymers) to achieve hybrid properties and coupling performances for practical applications. Attempts to assemble nanomaterials onto macroscopic materials are often accompanied by the loss of exceptional nanoscale properties during the fabrication process, which is mainly due to the poor contacts between carbon nanomaterials and macroscopic bulk materials. In this work, we proposed a novel cross-scale manufacturing concept to process disparate materials in different length scales and successfully demonstrated an electrothermal shock approach to process the nanoscale material (e.g., carbon nanotubes) and macroscale (e.g., glass fiber) with good bonding and excellent mechanical property for emerging applications. The excellent performance and potentially lower cost of the electrothermal shock technology offers a continuous, ultrafast, energy-efficient, and roll-to-roll process as a promising heating solution for cross-scale manufacturing.

Hierarchical Composites with Electrophoretically Deposited Carbon Nanotubes for In Situ Sensing of Deformation and Damage

As composites are used increasingly in structural components, novel techniques for detecting micro-scale damage are required. Their nanoscale size and high aspect ratio allow carbon nanotubes to create electrically conductive pathways that enable sensing. In this work, carbon nanotubes are deposited onto glass fabric using electrophoretic deposition to create hierarchical composites. Polyethylenimine functionalized carbon nanotubes are deposited from an aqueous dispersion using an electric field. Symmetric cross-ply composites are investigated as a model system to demonstrate the ability to detect incipient damage and transverse microcracks. The specimens are subjected to tensile loading, and a resistance increase is observed because of two key mechanisms-a reversible change in nanotube-nanotube tunneling gaps due to elastic straining of the network and a permanent severing of paths in the conducting network due to formation of transverse cracks in the 90° plies. By analyzing the electrical response, the damage state can be identified. Acoustic emission sensors are used to validate the results. The strength and Young's modulus of the composites with integrated carbon nanotubes are similar to the control specimens. Crack density measurements using edge replication reveal that transverse cracking can be suppressed, demonstrating multi-functionality with improved damage tolerance and integrated sensing.