Polymer Chain Dynamics in Intercalated Poly(ε-caprolactone)/Nanoplatelet Blends

The dynamics of poly­(ε-caprolactone) (PCL) blends with small amounts of Cloisite 30B nanoplatelets were investigated via broadband dielectric relaxation spectroscopy. The terminal relaxation, or normal mode of PCL, was found to be strongly influenced by the presence of the nanoplatelets, exhibiting a relaxation from PCL chains within the Cloisite platelets as well as a bulk-like relaxation. These results, as well as X-ray scattering and rheological results from the literature, help to form a clearer picture of how the structure and dynamics relate to the bulk physical properties in these systems. Cloisite was observed to have minimal impact on both the glassy state dynamics as well as the segmental dynamics, due to the relatively weak interactions between the polymer and the platelets

Overcoming the structural versus energy dissipation trade-off in highly crosslinked polymer networks: Ultrahigh strain rate response in polydicyclopentadiene

Ballistic performance, at effective strain rates of (104–105 s-1), for polymeric dicyclopentadiene (pDCPD) was compared with two epoxy resin/diamine systems with comparable glass transition temperatures. The high rate response was characterized in terms of a projectile penetration kinetic energy, KE50, which describes the projectile kinetic energy at a velocity with a 50% probability of sample penetration. pDCPD showed superior penetration resistance, with a 300–400% improvement in ballistic energy dissipation, when compared with the structural epoxy resins. In addition, unlike typical highly crosslinked networks that become brittle at low temperatures, the improved pDCPD performance occurred over a very broad temperature range (55 to 75 ˚C), despite exhibiting a glass transition temperature characteristic of structural resins (~142 ˚C). In addition to the high Tg, pDCPD exhibited a room temperature glassy storage modulus of 1.7 GPa, offering the potential to circumvent the common structural versus energy dissipation trade-off encountered with conventional crosslinked polymers. Quasi-static measurements suggested that the performance of pDCPD is phenomenologically related to higher fracture toughness and lower yield stress relative to typical epoxies, while molecular dynamics simulations suggest the origin is the lack of strong non-covalent interactions and the facile formation of nanoscale voids to accommodate strain in pDCPD

Dynamics of supersonic microparticle impact on elastomers revealed by real–time multi–frame imaging

Understanding high–velocity microparticle impact is essential for many fields, from space exploration to medicine and biology. Investigations of microscale impact have hitherto been limited to post–mortem analysis of impacted specimens, which does not provide direct information on the impact dynamics. Here we report real–time multi–frame imaging studies of the impact of 7 μm diameter glass spheres traveling at 700–900 m/s on elastomer polymers. With a poly(urethane urea) (PUU) sample, we observe a hyperelastic impact phenomenon not seen on the macroscale: a microsphere undergoes a full conformal penetration into the specimen followed by a rebound which leaves the specimen unscathed. The results challenge the established interpretation of the behaviour of elastomers under high–velocity impact.United States. Office of Naval Research (ONR DURIP Grant No. N00014-13-1-0676)United States. Army Research Office (Grant W911NF-13-D-0001

Ordering and Crystallization of Entangled Polyethylene Melts under Uniaxial Tension: A Molecular Dynamics Study

ISSN:1520-5835ISSN:0024-929