Abstract
We investigate nanoparticle (NP) dispersion, polymer conformations, entanglements and dynamics in ionic nanocomposites. To this end, we study nanocomposite systems with various spherical NP loadings, three different molecular weights, two different Bjerrum lengths, and two types of charge-sequenced polymers by means of molecular dynamics simulations. NP dispersion can be achieved in either oligomeric or entangled polymeric matrices due to the presence of electrostatic interactions. We show that the overall conformations of ionic oligomer chains, as characterized by their radii of gyration, are affected by the presence and the amount of charged NPs, while the dimensions of charged entangled polymers remain unperturbed. Both the dynamical behavior of polymers and NPs, and the lifetime and amount of temporary crosslinks, are found to depend on the ratio between the Bjerrum length and characteristic distance between charged monomers. Polymer–polymer entanglements start to decrease beyond a certain NP loading. The dynamics of ionic NPs and polymers is very different compared with their non-ionic counterparts. Specifically, ionic NP dynamics is getting enhanced in entangled matrices and also accelerates with the increase of NP loading.
Highlights
Having equilibrated all the ionic nanocomposites we are in the position to analyze their structural and morphological properties based on the available trajectories of monomers and NPs
We investigated the structure, conformations and dynamics of unentangled and entangled polymers in ionic nanocomposites, up to approximately 40% NP loading, using a coarse-grained model for ionic polymers and NPs by means of molecular dynamics simulations
We observed structural and dynamical behavior different from that known for conventional nanocomposites
Summary
Polymer nanocomposites have received special attention from academia and industry during the last 30 years, due to their improved properties [1,2,3,4,5,6,7] in comparison to polymer blends.Nanoparticle (NP) dispersion [8,9,10,11,12,13,14,15] is necessary for effective reinforcement [9,16] in the matrix and is a prerequisite for property “tuning” [17] and enhancement. One way to provide NP dispersion is to let the interaction between NPs and chains to be of an ionic nature [18,19,20]. The presence of oppositely charged ions at the polymer/nanofiller interphase can promote dispersion [21,22,23,24,25]. This relatively new class of ionic nanocomposites combines filler reinforcement with the reversibility of ionic interactions [23]. Despite the improved mechanical performance, the reversible feature of ionic bonds, that can break and reform under certain conditions [21], has led to smart materials for self-healing [25,26], shape-memory [21,22], piezoelectric [27], and mechanochromic [28] applications
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