Detailed atomistic modeling

This monograph deals with kinetics, not with dynamics. Dynamics, the local (coupled) motion of lattice constituents (or structure elements) due to their thermal energy is the prerequisite of solid state kinetics. Dynamics can explain the nature and magnitude of rate constants and transport coefficients from a fundamental point of view. Kinetics, on the other hand, deal with the course of processes, expressed in terms of concentration and structure, in space and time. The formal treatment of kinetics is basically phenomenological, but it often needs detailed atomistic modeling in order to construct an appropriate formal frame (e.g., the partial differential equations in space and time). 

A method for the detailed atomistic modelling of amorphous glassy polymers has been developed [50] and applied to atactic polypropylene. 

A method for the detailed atomistic modelling of amorphous glassy polymers has been developed [50] and applied to atactic polypropylene. This method has been described in Sect. 5.4. The quasi-static modelling of chain dynamics [51] has been described in Sect. 5.4.2. 

The diffusion coefficient of small penetrants in glassy polymers can also be correlated with the polymer free volume. In view of the fact that experimental techniques for the determination of the free volume are inherently difficult, Shah, Stern, and Ludovice (Shah, V.M. Stern, S.A. Ludovice, P.J., submitted for publication in Macromolecules) have utilized the detailed atomistic modeling of relaxed polymer glasses developed by Theodorou and Suter ( 2, 3) to estimate the free volume available in polymer glasses for the diffusion of small molecules. 

Molecular dynamics simulations using atomistic models, and hence relatively detailed potentials of interatomic interactions, of surfactants and solvent molecules [9,10] have been attempted for studying surfactant assemblies. However, as mentioned earlier, detailed atomistic modeling approaches demand intensive computations and as a result require drastic simplifications that prevent examination of certain aspects of structural or temporal features of the system. One such example is an a priori selection of the structure of the micelle itself in the simulations this clearly precludes the potential use of the simulations to examine the self-assembly process. 

Detailed Atomistic Modeling of Si(llO) Passivation by Atomic Layer Deposition of AI2O3... 

All major simulation techniques described in the rest of this book are applicable to these simplified models, as well as to the detailed atomistic models. Simulations of the simplified models, however, require much less computer power. They are helpful in studying phenomena where universal chain characteristics, such as chain length, flexibility, and topology are of interest. 

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. 

The outline of this article is as follows after a short discussion of some of the models (Sect. 2) we recall the basic aspects of MD and MC methods (Sect. 3). Results of simulations of chemically detailed atomistic models for short alkanes, polyethylene melts, and polybutadiene melts are mentioned. Section 4 is devoted to a discussion of coarse-grained models for the description of the phase behavior of alkanes in various solvents (Sects. 4.1 and 4.2). Also, qualitative models for semiflexible polymers that exhibit nematically ordered phases [121-123] and for block copolymer solutions that exhibit micelle formation [124, 125] will be discussed. Section 5 presents our conclusions. 

The past decade has seen steadily growing activity in the detailed atomistic modeling of polymer melts and glasses using energy minimisation and molecular dynamics simulation.These studies have been aimed at achieving an atomistic level understanding of a variety of physical properties such as stress-strain behavior, diffusion of small solute molecules and local chain motions. Because of its relative simplicity, polyethylene has come under a... 

---