Atom-based modeling of amorphous 1,4-cis-polybutadiene

Abstract

The structure of amorphous 1,4-cis-polybutadiene is simulated with molecular mechanics and molecular dynamics subjected to periodic boundary conditions. All hydrogen atoms are explicitly taken into account. By means of the relaxation strategy which has been developed in this work, the low-energy states of relatively large systems can be reached within an acceptable computational time. With the five simulated structures, the distribution of bond angles, distribution of dihedral angles, and correlated distribution of pairs of neighbor dihedral angles, as well as cohesive energy, solubility parameter, and atom pair radial distribution functions, are evaluated and discussed.

Detailed Atomistic Molecular Dynamics Simulation of cis-1,4-Poly(butadiene)

“…As far as the distributions of the torsion angles corresponding to dihedrals 1 and 2 are concerned, these were found to be in agreement with previous simulations studies such as those of Li and Mattice, 3 Smith and Paul, 9 and the recent EBMC simulation work of Gestoso et al 41 The distribution of dihedral φ 2 was seen to exhibit a maximum at around (118°and that of φ 1 at (180°and (60°( corresponding to the trans and gauche conformational states, respectively). It was further observed that as the temperature decreases (a) the height of the two torsionangle distributions at their peak increases (i.e., the relative population of states residing at the global minimum increases), (b) the population of the trans state (at (180°) in the distribution of the φ 1 dihedral increases accompanied by an increase in the population of the two gauche states, and (c) the trans population of φ 2 dihedral decreases.…”

Prediction of Structure and Energy of Trans-1,4-Polybutadiene Glassy Surface by Atomistic Simulations of Free-Standing Ultrathin Films

“…The edge length of the simulation cell was decided in the simulation depending upon the density and the total molecular weight of the three chains. This size of Downloaded by [Temple University Libraries] at 03:00 21 November 2014 the periodic box is greater than the sizes previously used in polybutadiene simulations [7][8][9] and satisfies the persistence length criterion [42] that the cell dimensions should be greater than twice the value of the persistence length of the polymer.…”

“…The experimental value [44] of solubility parameter that is reported for polybutadiene (stereochemical composition not presented) is in the range 8.1-8.6 cal 1/2 /cm 3/2 . [41] The statistics on the individual values of the solubility parameter of the sample of structures here are acceptable on the basis of the standard deviation and by comparison with experimental data and with those available from earlier studies on such atomistic models [7,8,[21][22][23]28,42] for various polyolefins and slightly polar polymers.…”

“…The "Doublepar" force field, which is a modification of the Dreiding force field and has proven to be successful previously for modeling of polybutadienes, [7][8][9] was used in this study. The potential parameters specific to polybutadienes were taken from the original work of De Rosa et al [39] The overall potential energy for each of the structures, i.e., the Downloaded by [Temple University Libraries] at 03:00 21 November 2014 2204 A. S. Ijantkar and U. Natarajan decomposition of force-field terms, is given by…”

“…Earlier MD simulation studies on the four microstructures formed by 1,4-cis-polybutadiene, 1,4-transpolybutadiene, 1,2-vinyl-polybutadiene, and a random copolymer of these stereochemical structures (55% trans, 35% cis, and 10% vinyl) looked at their single chain and bulk amorphous structural properties. [7][8][9] Regarding the simulations on properties of polymer surfaces, studies in the literature have employed lattice MC, [10][11][12] off-lattice MC, [13][14][15] and lattice-fluid models. [16,17] The molecular modeling approach was later extended to that having a full atomistic description of real chains in continuum space using approaches such as the EM of the one-sided free-surface (for atactic polypropylene), [18] MD simulations of chain collapse into a thin film, [19] and the two-dimensional (2D) thin film nonbonded interactions methodology in molecular mechanics and MD simulations by removal of periodicity in one direction, [20][21][22][23][24] for chemically different nonpolar and slightly polar polymers and copolymers.…”