End grafted polymernanoparticles in a polymeric matrix: Effect of coverage and curvature

Abstract

It has recently been proposed that the miscibility of nanoparticles with a polymer matrix can be controlled by grafting polymer chains to the nanoparticle surface. As a first step to study this situation, we have used molecular dynamics simulations on a single nanoparticle of radius R (4σ ≤R≤ 16σ , where σ is the diameter of a polymer monomer) grafted with chains of length 500 in a polymer melt of chains of length 1000. The grafting density Σ was varied between 0.04-0.32 chains/σ 2 . To facilitate equilibration a Monte Carlo doublebridging algorithm is applied -new bonds are formed across a pair of chains, creating two new chains each substantially different from the original. For the long brush chains studied here, the structure of the brush assumes its large particle limit even for R as small as 8σ , which is 1 consistent with recent experimental findings. We study autophobic dewetting of the melt from the brush as a function of increasing Σ. Even these long brush and matrix chains of length 6 and 12 N e , respectively, (the entanglement length is N e ∼ 85) give somewhat ambiguous results for the interfacial width, showing that studies of two or more nanoparticles are necessary to properly understand these miscibility issues. Entanglement between the brush and melt chains were identified using the primitive path analysis. We find that the number of entanglements between the brush and melt chains scale simply with the product of the local monomer densities of brush and melt chains.

Structure of Polymer Layers Grafted to Nanoparticles in Silica–Polystyrene Nanocomposites

“…The corona structure factors for 13-nm-radius grafted particles dispersed in different molar mass matrices have been validated against experimental findings of Chevigny et al 39 The present study is limited to the case of a single nanoparticle immersed in a homogeneous polymer matrix. As Kalb et al 21 stated, simulations of a single particle at infinite dilution cannot reveal the critical conditions that distinguish aggregation from dispersion. It is highly interesting to analyze the collective effects on the structure of the brush and the melt when two or more nanoparticles are present at experimental volume fractions.…”

“…21 The phase transition has been attributed to the autophobic dewetting of the brush by the melt. (ii) Increasing the brush chain length leads to thicker grafted brushes, which improve the miscibility of nanoparticles with the homopolymer matrix, in agreement with SCF studies.…”

“…This is why a variety of mesoscopic techniques have been developed for these particular systems. Kalb et al 21 and later Meng et al 22 have performed Molecular Dynamics simulations where both brush and melt chains were represented using the coarse-grained beadspring model of Kremer and Grest. 23 One of their conclusions was that the conformational transition between a stretched "wet" brush and a collapsed "dry" brush, which has been attributed to the autophobic dewetting of the brush by the melt, was not readily apparent in their brush density profiles.…”

Perspective: Outstanding theoretical questions in polymer-nanoparticle hybrids

“…While functional groups can be introduced on the polymer chains to aid in this miscibility, a more popular and generalizable strategy is to functionalize the NP with either small ligand molecules or larger polymeric grafts. In addition to aiding in the miscibility of the mixture, 28,32,34,[41][42][43][44][45][46][47][48][49] interestingly, in some instances, the polymer grafting strategy has been shown to convert the NPs into a new class of amphiphiles. This new functionality allows them to self-assemble into a variety of superstructures reflecting their hydrophilic/hydrophobic balance.…”

Dynamics in coarse-grained models for oligomer-grafted silica nanoparticles

“…10,11 Such models have been used to investigate morphologies, [12][13][14] structure and dynamics, [15][16][17][18][19] mechanical properties, [20][21][22] and rheological behavior 21,23 of nanocomposites, grafted nanoparticles in a polymer matrix, and NOHMs. a) Electronic mail: azp@princeton.edu.…”