Unusual dynamics of ring probes in linear matrices

Abstract

We perform Monte Carlo simulations of ring and linear polymers in linear matrices, and investigate the diffusivity of the probes. As the matrix chain length Nm is increased from 10 to 300 monomers, the diffusivity Dl of a linear probe (Nl = 300) decreases monotonically, while that of a ring probe Dr varies non‐monotonically, with a peak around Nm≈30−75. We perform additional simulations with a single probe molecule ( Nr=Nl=150) in a linear matrix ( Nm=10−150). The non‐monotonicity in Dr persists even after ring–ring interactions are eliminated. Topology dependent differences in the short‐time dynamics of the probes are observed; unlike linear probes, mean‐squared displacements of ring probes depend on Nm. Primitive path analysis suggests that the difference in dynamics originates from differences in entanglement structure. For linear probes, the degree of entanglement is independent of Nm. For ring probes, we observe two regimes: when Nm is small, the number of threadings decreases as Nm increases, eventually transitioning to a plateau. In the small Nm regime, the change in the degree of entanglement offsets the change in the mobility of the matrix chains, leading to a non‐monotonic variation in Dr. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 169–177

Relation between Polymer Conformational Structure and Dynamics in Linear and Ring Polyethylene Blends

“…Originally, Cates and Deutsch suggested that the topologically induced EV interactions in the ring melt are relieved upon diluting the rings by linear chains so that the rings in the melt should become “ideal” upon dilution by linear chains. Recent simulations and experiments on ring‐linear polymer blends have reported that rings increase their size upon the dilution and their conformational structure resembles ideal rings in a theta solvent, clearly supporting a change in the EV interactions in ring melts upon adding linear chains. Moreover, the rate of diffusion of tracer ring polymers in the melt was found to be greatly slowed by adding linear chains, an effect interpreted as arising from the ring‐linear polymer threadings .…”

“…Recent simulations and experiments on ring‐linear polymer blends have reported that rings increase their size upon the dilution and their conformational structure resembles ideal rings in a theta solvent, clearly supporting a change in the EV interactions in ring melts upon adding linear chains. Moreover, the rate of diffusion of tracer ring polymers in the melt was found to be greatly slowed by adding linear chains, an effect interpreted as arising from the ring‐linear polymer threadings . Although there have been many attempts at quantifying this physically appealing “threading effect,” the validity of the threading model has not yet been established.…”

“…This phenomenon has been considered in previous work, but the nature of this swelling process is not yet entirely clear, and the present work is devoted to further elucidating this problem from a new perspective not relying on the reptation model. There have admittedly been numerous arguments, experiments, and simulations pertaining to the configurational properties and dynamics of rings diluted by linear chains. Originally, Cates and Deutsch suggested that the topologically induced EV interactions in the ring melt are relieved upon diluting the rings by linear chains so that the rings in the melt should become “ideal” upon dilution by linear chains.…”

Ring and Linear Copolymer Blends under Confinement

“…Although the change of size within the considered interaction range is small its overall effect on the domain size is significant as indicated by the significant shift in the peak position of S(q). Note that the swelling of ring polymers upon addition of small molecules/solvents and linear polymers in the case of homopolymers has been observed in earlier studies, [15][16][17] however it is reported that the nature of swelling is not clear. And in a recent study by Jeong and Douglas it is shown that the swelling arises from altered self-excluded volume interactions which amplifies in the entangled regime.…”

“…For example, sufficiently long ring polymers are shown to behave as compact object (i.e., size ∼ N 1/3 with N chain length), also unexpected power-law stress relaxation is observed in entangled ring polymers, [8][9][10][11] and smaller diffusion coefficient [12]. Interesting observations are made in case of ring-linear blends, e.g., it shows enhancement of miscibility due to the topological entropy gain of rings upon mixing with linear chains, [13,14] swelling of rings and unusual dynamics of rings in the matrix of linear chains, [15][16][17] and dramatic increase of viscosity of linear melts by adding rings [18]. Recent efforts in understanding the equilibrium and out-of-equilibrium properties of ring * slenin2001@gmail.com polymers focus mainly on homopolymers.…”