COMPUTER-SIMULATION STUDY OF THE CONFORMATIONAL STATISTICS OF LONG-CHAIN HYDROCARBONS IN CYLINDRICAL POTENTIALS

The Monte Carlo method is applied to the study of disordered conformations of polymethylene chains confined in cylindrical mean-field potentials. It is assumed that the molecule, which is composed of 30 united atoms (methylene groups), has fixed bond length and bond angle, and makes quasicontinuous bond rotations. Various statistical properties of the molecule, such as dihedral angle distributions, dihedral angle pair correlations, transverse fluctuations, etc., are calculated vs strength of the mean-field potential. The dihedral angle distributions calculated exhibit the marked reduction of the gauche peaks with increasing potential; it implies the increasing inaccuracy of the usual rotational isomeric model. The dihedral angle pair correlations reveal novel characteristics of the dihedral angle fluctuation: the fluctuation has approximate period of four bonds with marked tendency for the next nearest bonds to counter-rotate. The characteristics are more conspicuous under weaker potential constraint. There are large transverse fluctuations of the chain, the average linear form of the chain being still maintained. These characteristic dihedral angle fluctuation and the transverse deviation of the chain are found to be well understood by a small scale kink model. © 1990 American Institute of Physics.