Computer simulation of bottle-brush polymers with flexible backbone: Good solvent versus theta solvent conditions

摘要

By Molecular Dynamics simulation of a coarse-grained bead-spring type modelfor a cylindrical molecular brush with a backbone chain of $N_b$ effectivemonomers to which with grafting density $sigma$ side chains with $N$ effectivemonomers are tethered, several characteristic length scales are studied forvariable solvent quality. Side chain lengths are in the range $5 le N le 40$,backbone chain lengths are in the range $50 le N_b le 200$, and we perform acomparison to results for the bond fluctuation model on the simple cubiclattice (for which much longer chains are accessible, $N_b le 1027$, and whichcorresponds to an athermal, very good, solvent). We obtain linear dimensions ofside chains and the backbone chain and discuss their $N$-dependence in terms ofpower laws and the associated effective exponents. We show that even at theTheta point the side chains are considerably stretched, their linear dimensiondepending on the solvent quality only weakly. Effective persistence lengths areextracted both from the orientational correlations and from the backboneend-to-end distance; it is shown that different measures of the persistencelength (which would all agree for Gaussian chains) are not mutually consistentwith each other, and depend distinctly both on $N_b$ and the solvent quality. Abrief discussion of pertinent experiments is given.