Anomalous dynamics in 2D polymer melts

Computer Simulation Insight into the Adsorption and Diffusion of Polyelectrolytes on Oppositely Charged Surface

In the present work, by means of computer simulation, we studied the adsorption and diffusion of polyelectrolyte macromolecules on oppositely charged surfaces. We considered the surface coverage and the charge of the adsorbed layer depending on the ionization degree of the macromolecules and the charge of the surface and carried out a computer experiment on the polymer diffusion within the adsorbed layers, taking into account its strong dependency on the surface coverage and the macromolecular ionization degree. The different regimes were distinguished that provided maximal mobility of the polymer chains along with a high number of charged groups in the layer, which could be beneficial for the development of the functional coatings. The results were compared with those of previous experiments on the adsorption of polyelectrolyte layers that may be applied as biocidal renewable coatings that can reversibly desorb from the surface.

Intrinsic structure and dynamics of monolayer ring polymer melts

We present the general structural and dynamical characteristics of flexible ring polymers in narrowly confined two-dimensional (2D) melt systems using atomistic molecular dynamics simulations. The results are further analyzed via direct comparison with the 2D linear analogue as well as the three-dimensional (3D) ring and linear melt systems. It is observed that dimensional restriction in 2D confined systems results in an increase in the intrinsic chain stiffness of the ring polymer. Fundamentally, this arises from an entropic penalty on polymer chains along with a reduction in the available chain configuration states in phase space and spatial choices for individual segmental walks. This feature in combination with the intermolecular interactions between neighboring ring chains leads to an overall extended interpenetrated chain configuration for the 2D ring melt. In contrast to the generally large differences in structural and dynamical properties between ring and linear polymers in 3D melt systems, relatively similar local-to-global chain structures and dynamics are observed for the 2D ring and linear melts. This is attributed to the general structural similarity (i.e., extended double-stranded chain conformations), the less effective role of the chain ends, and the absence of complex topological constraints between chains (i.e., interchain entanglement and mutual ring threading) in the 2D confined systems compared with the corresponding 3D bulk systems.

Entropy-mediated mechanical response of the interfacial nanoparticle patterning

The precise organization of nano-objects into well-defined patterns at interfaces is an outstanding challenge in the field of nanocomposites toward technologically important materials and devices. Herein, by means of computer simulations we show novel mechanomutable nanocomposites designed by binary mixtures of tethered Janus nanoparticles at the interface of a binary fluid mixture under mechanical pressure. Our simulations demonstrate that the nanoparticle organization in the systems undergo reversible transition between random state and long-ranged intercalation state, controlled by various structural parameters of the tethered chains and the applied pressure. The dynamical mechanism during the transition is explored through examining the diffusion trajectories of the nanoparticles confined at the interfaces. We provide a theoretical analysis of the lateral pressure induced by the tethered chains, which is fully supported by simulation data and reveals that the compression-induced transition is fundamentally attributed to the entropic effect from the tethered chains. Our study leads to a class of interface-reactive nanomaterials in which the transfer and recovery of interfacial nanopatterning presents precise and tunable mechanical responses.