MSc Students Presentations - George Papadopoulos

Through this work, blends of ring and linear poly(ethylene oxide) (PEO) molecules have been studied, a widely used polymer, with well-known characteristics. The main focus was on ring PEO molecules, as they exhibit material properties that are very different from those of linear analogues, due to the absence of chain ends and their closed-loop structure.

We have performed molecular dynamics (MD) simulations of melt systems consisting of a small number of long ring poly(ethylene oxide) (PEO) molecules immersed in a host matrix of linear PEO chains, following a recent neutron spin echo spectroscopy study (Goossen et al., Phys. Rev. Lett. 2015, 115, 148302). The results are compared with the experimental data of the work above, and include a thorough study on the structure, the conformational properties and the dynamics of the simulated blends. These regard calculations such as the segmental and the diffusion dynamics, the dynamic structure factor and a comparison with the Rouse model, emphasizing on their dependence on the length of the host linear chains. Interestingly, in unentangled matrices ring chains swell and their diffusion dynamics become evidently faster. Our results are supported by a geometric analysis of topological interactions between the linear and the ring molecules, which reveals significant threading of all rings by the linear chains. In most cases, each ring is simultaneously threaded by a large number of linear chains. As a result, ring dynamics at times longer than τ_e is completely dictated by the release of the topological restrictions imposed by these threading events. Our topological analysis did not indicate any effect of the few rings on the statistics of the network of primitive paths of the host linear chains.