The behavior of polymer melts under cylindrical confinement was investigated using molecular dynamics simulations. A range of polymer chains, from unentangled to highly entangled, were confined in cylindrical pores with radii ranging from much smaller to much larger than the polymer size. These simulations were used to measure polymer chain conformation, entanglement density, and center-of-mass diffusion. The conformational anisotropy is well-described by a confined random walk model, although excluded volume effects cause slight differences in the radius of gyration. The number of entanglements per chain in confinement is accurately described using a simple volume fraction model consisting of a zero-entanglement region near the pore wall and a bulklike entanglement region in the pore center. The size of the depletion region near the wall is chain length dependent. Finally, the diffusion along the pore axis exhibits nonmonotonic behavior with the pore radius. As the pore radius decreases, the diffusion coefficient, D, initially increases due to increasing chain disentanglement, though for small pores D eventually decreases as a result of confinement-induced chain segregation.

The addition of nanoparticles attenuates creep deformation in polymer nanocomposites; networked nanoparticle morphologies are more effective.

The behavior of polymer melts under planar confinement was investigated using molecular dynamics simulations. Polymers with a range of lengths, from unentangled to highly entangled (N = 25–400), were confined between two discrete-bead parallel walls to create thin films with thicknesses (h = 3.5–40σ, where σ is the unit length) ranging from much larger to much smaller than the polymer size. These simulations were used to measure polymer-chain conformations, entanglement densities, and center-of-mass diffusion, and the results were compared with previous simulations of polymer melts under cylindrical confinement. Changes to the entanglement density and radius of gyration in thin films follow the same behavior as in cylindrical confinement: decreased entanglements per chain, decreased R g perpendicular to the confining wall, and increased R g parallel to the confining wall, though the deviations from bulklike conformations are smaller. Despite similarities in conformation and entanglement behavior between thin-film and cylindrical confinements, the diffusion behavior differs. Under planar confinement, the diffusion coefficient increases monotonically up to 6 times the bulk diffusivity with decreasing film thickness, while it behaves nonmonotonically in cylinders. This is due to the increased degrees of freedom afforded to the polymer chains in a thin film compared to those in a cylinder, allowing chains to diffuse around one another rather than through, as found in cylindrical confinement. Normalized diffusion coefficients, D norm, can be well described by a master curve with an exponential dependence on confinement after scaling D norm by a thickness-dependent term.

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A parallel automated track collector is integrated with a rationally designed centrifugal spinning head to collect aligned polyacrylonitrile (PAN) nanofibers. Centrifugal spinning is an extremely promising nanofiber fabrication technology due to high production rates. However, continuous oriented fiber collection and processing presents challenges. Engineering solutions to these two challenges are explored in this study. A 3D-printed head design, optimized through a computational fluid dynamics simulation approach, is utilized to limit unwanted air currents that disturb deposited nanofibers. An automated track collecting device has pulled deposited nanofibers away from the collecting area. This results in a continuous supply of individual aligned nanofibers as opposed to the densely packed nanofiber mesh ring that is deposited on conventional static post collectors. The automated track collector allows for simple integration of the postdraw processing step that is critical to polymer fiber manufacturing for enhancing macromolecular orientation and mechanical properties. Postdrawing has enhanced the mechanical properties of centrifugal spun PAN nanofibers, which have different crystalline properties compared with conventional PAN microfiber. These technological developments address key limitations of centrifugal spinning that can facilitate high production rate commercial fabrication of highly aligned, high-performance polymer nanofibers.