Rouse mode analysis of chain relaxation in polymer nanocomposites

Abstract

Large-scale Molecular Dynamics simulations are used to study the internal relaxations of chains in nanoparticle (NP)/polymer composites. We examine the Rouse modes of the chains, a quantity that is closest in spirit to the self-intermediate scattering function, typically determined in an (incoherent) inelastic neutron scattering experiment. Our simulations show that for weakly interacting mixtures of NPs and polymers, the effective monomeric relaxation rates are faster than in a neat melt when the NPs are smaller than the entanglement mesh size. In this case, the NPs serve to reduce both the monomeric friction and the entanglements in the polymer melt, as in the case of a polymer-solvent system. However, for NPs larger than half the entanglement mesh size, effective monomer relaxation is essentially unaffected for low NP concentrations. Even in this case, we observe a strong reduction in chain entanglements for larger NP loadings. Thus, the role of NPs is to always reduce the number of entanglements, with this effect only becoming pronounced for small NPs or for high concentrations of large NPs. Our studies of the relaxation of single chains resonate with recent neutron spin echo (NSE) experiments, which deduce a similar entanglement dilution effect.

Perspective: Outstanding theoretical questions in polymer-nanoparticle hybrids

“…Similar results have been found for spherical NPs in polymer melts. 106,227 These simulations, combined with recent experiments showing that the diffusion coefficient of polymers in the presence of nanorods can exhibit non-monotonic changes with nanorod concentration (see Fig. 5), suggest that there is still much to understand about the dynamics of polymer nanocomposites.…”

“…97,106,107,[218][219][220][221] Furthermore, since in the tube model the diffusivity is proportional to the ratio of the molecular weight between entanglements to the monomer friction coefficient, D ∼ N E /ζ, these effects will likely only be meaningfully distinguished through their temperature dependence. In turn, NP dynamics as they move through an entangled polymer melt is also an area of active interest.…”

“…(i) Phase diagrams: The theoretical/simulation works of Schweizer,46,[75][76][77][78][79] Striolo,60,[80][81][82][83] Roan,84,85 Pakula, 86,87 Jayaraman, 24,37,[88][89][90][91][92][93][94][95] de Pablo, [96][97][98][99][100][101][102] Panagiotopoulos, 50,56,[103][104][105] Grest, 34,42,71,[106][107][108][109][110][111][112][113][114] …”

Local and Global Dynamics in Polypropylene Glycol/Silica Composites

“…Simulations suggest that attraction to the particle surface expands the size of the interfacial chains [34], presumably affecting their motion. For the rheological properties, simulations suggest a reduction in entanglements as the origin of enhanced mobility [35].…”

Static and dynamic properties of large polymer melts in equilibrium

“…It is well known that for short unentangled chains in a melt, the motion of monomers can be approximately described by the Rouse model [1,[6][7][8]. If the polymer chains become long enough such that the effects of entanglements start to become important, movements of chains at the intermediate time and length scales are confined to a tube-like region, created by surrounding chains and depending on the corresponding entanglement length N e .…”