Using dynamic Monte Carlo simulations based on the bond-fluctuation model, we systematically investigate the static and dynamic properties of a tracer ring polymer in a melt composed of linear polymers. Our results reveal that the mean-square radius of gyration of a cyclic polymer is independent of the topological constraints between the ring and linear chains. The scaling exponent (ν) of the radius of gyration R g ∼ N R ν, where N R is the ring chain length, increases from 0.5 to 0.6 as the length of the linear matrix chains, N L, decreases, which lies between the two values reported by Iyer et al. [Macromolecules2007405995] and Lang et al. [Macromolecules2012457642]. We find that both the structural relaxation time and self-diffusion coefficient are nearly independent of N L for a short ring chain (N R = 20) and the scaling exponents of N L for the self-diffusion coefficient are between −1 and −2 for large N R (N R ≥ 100), which cannot be understood by existing mechanisms, including the restraint reptation mechanism, the once-threaded mechanism, and the constraint release mechanism. Furthermore, we propose a “touch-threading” mechanism, which could be regarded as an important supplement to the above mechanisms, to describe the structural relaxation and translational diffusion of a tracer ring in a linear melt. In addition, when N L is large, the structural relaxation and translational diffusion of the tracer ring are decoupled, resulting in a breakdown of the extended Stokes–Einstein relation. These results provide fundamental insights into the properties of the ring-linear blends.

Flow-induced translocation of linear and ring polymers is studied by using a combination of multiparticle collision dynamics and molecular dynamics. The results show that both end capture and fold capture are present in the capture process of linear chains in weak flows, whereas fold capture becomes dominant in strong flows, resulting in similar behavior for the linear and ring chains in the strong flow regime. For narrow channels, the critical flux decreases with the increase of channel size, which is qualitatively consistent with the prediction by Wu et al.; for large channel sizes (which are still smaller than the polymer size), the critical flux is independent of channel size, in agreement with an earlier prediction by de Gennes et al. The presence of these two scaling regimes indicates that the confined blob exhibits a crossover from free draining to nondraining as the channel size increases. Moreover, we found that the conformation of the polymer exhibits a flow-induced coil–compact–stretch transition, and the transition does not appear to be first order. In addition, we observed that the monomers far from the channel and in the channel exhibit independent dynamics.