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

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The multiscale structure-interphase-property relationships observed for FRP hierarchical composites were measured using techniques sensitive to electronic structure, neutron scattering, viscoelastic relaxations, and polymer dynamics.

ACS Multiscale Composite Characterization
Figure 1: The multiscale structure-interphase-property relationships observed for FRP hierarchical composites. Left: Gallium Ion image showing the percolated CNT network (bright regions) surrounding the microscale fibers and the epoxy matrix. Right, top: Broadening of polymer relaxation and (Right, bottom) increase in polymer mobility at the nanoscale lengths due to the presence of the nanocomposite interface.
Fiber reinforced structural composites (FRP) are essential for lightweighting of vehicles; for elimination of costly autoclave manufacturing processes; or for creation of more durable infrastructure components with self-sensing capabilities. However, improving the both the inter- and intra-laminar properties remains a challenge. High aspect ratio nanofillers can address these challenges, but manufacturing challenges associated with incorporating nanofillers throughout the composite have hindered progress. One viable method of overcoming this limitation involves grafting functionalized carbon nanotubes onto continuous microfiber surfaces (such as glass and carbon) before polymer resin infusion using an electrophoretic deposition technique. This is a scalable method of nanocomposite manufacture that provides material with superior mechanical, electrical and thermal properties compared to a non-modified fiber composite.

Given the large area of the of the interface generated through this processing method, the potential for polymer relaxation to affect long term mechanical properties should be evaluated. For example, changes in the conductivity of the CNT network may from polymer matrix relaxation. The measurement challenge is now to quantify the effect of these complex nanofiller-polymer-fiber interfaces on the time-dependent properties of the composite. Here we apply a suite of microscale and nanoscale characterization methods to probe the structure, viscoelastic properties, and nanoscale polymer dynamics in these complex architectures.  In particular, we find that the functionalized CNT interface creates a percolated network around the fibers that results in subtle changes to the polymer dynamics. This interface exhibits a higher polymer mobility compared to the composite without nanofillers. These changes are evident at the length scale of the fibers (~ 10 m) down to the nanoscale of the polymer and functionalized CNTs. In the broader context of engineering applications, transport of small molecules (such as water, solvent, etc.), creep and stress relaxation, electrical conductivity and thermal expansion are inherently affected by the structural and viscoelastic variations studied in this paper.

Ajay Krishnamurthy, Ran Tao, Erkan Senses, Sagar M. Doshi, Faraz Ahmed Burni, Bharath Natarajan, Donald Hunston, Erik T. Thostenson, Antonio Faraone, Amanda L. Forster, and Aaron M. Forster “Multiscale Polymer Dynamics in Hierarchical Carbon Nanotube Grafted Glass Fiber Reinforced Composites” ACS Applied Polymer Materials 2019, 1, 1905-1917

Infrastructure, Composites, Materials characterization, Composition and structure, Mechanical properties, Nanomaterials and Neutron research
Released August 27, 2019, Updated September 26, 2019