A Molecular Dynamics Study of a Model Nanoparticle Embedded in a Polymer Matrix

Abstract

Molecular dynamics (MD) simulations have been used to examine the structure and dynamics of a system containing an inorganic nanoparticle embedded in a polymer matrix. This paper represents a preliminary investigation into the feasibility of examining such relatively large systems using atomistic modeling techniques. No attempt is made here to model any specific system. A generic linear polymer “united-atom” model is first created in an amorphous phase before the insertion of an atomistically detailed silica nanoparticle of diameter ∼4.4 nm. A novel method to insert a nanoparticle into a polymer matrix is given. The entire system is contained in a standard periodic simulation cell of side length ∼10 nm. The volume fraction of silica corresponded to ∼4.5%. The composite system was subsequently relaxed at 300 K and at two different pressures using standard MD techniques, the gmq suite of programs being used for this purpose. Results are presented regarding the variation of the structure and dynamics of the system with respect to the distance from the polymer−nanoparticle interface and as a function of pressure. A clear structuring of the polymer chains around the nanoparticle is seen with prominent first and second peaks in the radial density function and a concurrent development of preferred chain orientation. The probability of trans conformers is also higher close to the interface and shows a distinct gradient. In contrast, evidence for chain immobilization is less obvious overall although dynamic properties are more sensitive to changes in the pressure. Comparisons are also made between the bulk moduli of the pure polymer and composite systems.

Melt Compounding of Polymeric Nanocomposites

“…Mathematical modeling of CPNC has been used to describe structure of polyamide (PA) based CPNC [18,19]. The intercalant's ion charge was found dislocated and spread all over the molecule, causing it to stretch flat on the clay surface.…”

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.…”

Origin of particle clustering in a simulated polymer nanocomposite and its impact on rheology

“…Previous simulations have elucidated the detailed changes in structure and dynamics that occur near a nanoparticle surface [9][10][11][12] and possible mechanisms for reinforcement, 13 and theoretical approaches used to model colloidal systems have been adapted to predict morphologies of claylike nanocomposites. 14 Building on these works, we focus our attention on characterizing particle dispersion and bulk composite properties using molecular dynamics simulations of model nanoparticles embedded in a dense melt of unentangled polymers.…”