Molecular Dynamics Studies of Polymer Nano-particles

Molecular Dynamics Studies of Polymer Nano-Particles 

Molecular dynamics (MD) is an invaluable tool to study structural and dynamical details of polymer processes at the atomic or molecular level and to link these observations to experimentally accessible macroscopic properties of polymeric materials. For example, in their pioneering studies of MD simulations of polymers, Rigby and Roe in 1987 introduced detailed atomistic modeling of polymers and developed a fundamental understanding of the relationship between macroscopic mechanical properties and molecular dynamic events [183-186]. Over the past 15 years, molecular dynamics have been applied to a number of different polymers to study behavior and mechanical properties [187-193], polymer crystallization [194-196], diffusion of a small-molecule penetrant in an amorphous polymer [197-199], viscoelastic properties [200], blend [201,202] and polymer surface analysis[203-210]. In this article, we discuss MD studies on polyethylene (PE) with up to 120,000 atoms, polyethylproplyene (PEP), atactic polypropylene (aPP) and polyisobutylene (PIB) with up to 12,000 backbone atoms. The purpose of our work has been to interpret the structure and properties of a fine polymer particle stage distinguished from the bulk solid phase by the size and surface to volume ratio. 

A computational algorithm for generating and modeling polymer particles for our simulations was developed to construct particles that are as similar as possible to the experimentally created polymer particles. We have examined a variety of PE nano-scale particles, allowing the systematic study of size-dependent physical properties of these particles [214]. The models have been well tested and shown to provide realistic representation of the structure and vibrational spectroscopy of a number of polymer systems harmonic/Morse potentials for the bond stretches, harmonic potential for bending between two bonds, a truncated 

Fourier series for the torsional potential, and Lennard-Jones 6-12 potentials for the non-bonded interactions (both chain-chain and intra-chain) [193,215-218]. 

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