Interface between End-Functionalized PEO Oligomers and a Silica Nanoparticle Studied by Molecular Dynamics Simulations

Abstract

Fully atomistic molecular dynamics (MD) simulations have been carried out on a series of bulk melt pure PEO oligomers and PEO oligomer−silica systems, which differed by their macromolecular end groups. A realistic hybrid model of a silica nanoparticle combining an ionic core as well as the fine-tuning of the surface thickness and number of OH groups per unit surface area was used. The PEO oligomers were decorrelated in all systems under study in order to prevent any artifacts related to the preparation procedure. Significant changes were found to occur in the immediate vicinity of the interface with flattened PEO backbones arranged in densily packed shells and stabilized by the added PEO−silica interactions. Their conformations were also more coiled in order to better adapt to the surface structure. While methyl end groups did not show special characteristics other than their steric effect, hydroxyl end groups had a much higher affinity for the surface and tended to position themselves perpendicular to the surface, thus forming dynamic hydrogen-bonding complexes between the hydroxyl oxygens and the silanol hydrogens. The range of influence of the nanoparticle was evident for structural properties only up to two or three molecular layers, 10−15 Å, but was approximately twice that for dynamical ones.

Investigation of Thermal Expansion of Polyimide/SiO2 Nanocomposites by Molecular Dynamics Simulations

“…This fact is in agreement with the results presented in a number of other manuscripts devoted to investigations of interactions at solid interfaces. [9,[15][16][17][18]60,61] The formation of the first peak is due to the surface force, which has a short-range nature, and decreases $1/r 4 . [62] The comparison between the results for r(z) in the material samples [see Figure 8(a)-(c)] shows that the effect of the substrate on the density distribution is increasing with decreasing thickness of the polymer matrix.…”

A molecular dynamics simulation study of surface effects on gas permeation in free-standing polyimide membranes

“…To characterize chain alignment, the second order Legendre polynomial functions, P 2 (cos θ α ), were calculated where the angle θ α for a triplet of atoms {i, j, k} is that between the α-axis and the vector between atoms i and k [75]. This analysis was carried out for all so-called "pivot angles" which includes (see Fig.…”

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

“…Although models with atomistic descriptions of both nanoparticles and chains have been developed for nanocomposites, [4][5][6][7][8] their application is often limited to systems with one nanoparticle, and they can only provide information on local polymer structures (length scales <4 nm) over short times of the order of ns. In order to describe largerscale properties such as nanoparticle dispersion and transport, a NOHMs model with solid-sphere nanoparticles and atomistic polymers was recently proposed that is suitable for simulating systems consisting of hundreds of nanoparticles.…”