Finite chain length effects on the coil-globule transition of stiff-chain macromolecules: A Monte Carlo simulation

We study the effect of finite chain length on the collapse transition of stiff-chain macromolecules by means of a Monte Carlo simulation within the framework of the bond fluctuation lattice model. Variable stiffness of the chains was modeled by introducing a potential depending on the angle between successive bonds and we introduced an additional quasi-Lennard-Jones potential between monomer units which are not nearest neighbors along the chain to model the quality of the solvent. Chains of length up to 200 monomer units were simulated. For the flexible case these chains are long enough to determine the theta-temperature, but for higher stiffnesses we show systematic effects in the dependence of the apparent transition temperature on the stiffness. For fixed chain lengths we determine apparent phase diagrams and give the apparent transition points and points of ideal chain size as a function of stiffness. We report on the occurrence of a toroidal structure in our model and characterize this structure by local and global packing and orientational ordering. (C) 1998 American Institute of Physics. [S0021-9606(98)51837-5]