ON LYOTROPIC BEHAVIOR OF MOLECULAR BOTTLE-BRUSHES - A MONTE-CARLO COMPUTER-SIMULATION STUDY

A three dimensional continuous space Monte Carlo computer simulation s tudy is presented to discuss the extension of flexible, linear polymer chains due to the presence of equally flexible side chains. We consid er the enhancement of the persistence length of bottle-brush structure s in an athermal solution due to steric interactions between the side chains, The largest structure studied consists of a backbone of 100 be ads with 50 side chains of 20 beads each, The persistence length lambd a is evaluated in two different ways using the radius of gyration of t he backbone and the bond angle correlation function, respectively. A c orrect description of the backbone conformations is shown to require a t least two characteristic lengths. At a small length scale the backbo ne behaves flexible; the extension occurs at a larger length scale. Th ere is a strong indication that the ratio between the persistence leng th and the diameter, which is the determining factor for lyotropic beh avior of conventional semiflexible chains, levels off as a function of the side chain length. The value of this ratio is, moreover, too smal l to induce lyotropic behavior along this line. Recent experimental ob servations of lyotropic behavior of polymacromonomers are discussed in terms of these findings. (C) 1997 American Institute of Physics.