Molecular Dynamics Simulations of Bottle-Brush Polymers with a Flexible Backbone under Theta and Good Solvent Conditions

Abstract

Using molecu lar dynamics simulations of a standard bead-spring model for poly mer chains,bottle-brush polymerswith a flexib le backbone of Nbeffective units,where side chains of length N are grafted under theta and good solvent conditionsin the range 3.0 4.0 B Tk e = − , are studied.The range of backbone and side chains' length varies correspondingly as 50 200 b N ≤≤ and 5 40 N ≤≤ for t wo different grafting densities σ, namely σ=0.5 and 1.0.Even at temperatures T close to the theta point the side chains are significantly stretched, as it has been confirmed for bottle brushes with a rigid backbone, their linear dimension depending on the solvent quality only weakly. Ho wever, the distribution of monomers shows a more pronounced dependence, which we characterize through the asphericity and acylindricity as functions of σ, T, Nb, and N. In part icular, increase of σ, T, Nb, and N increases the normalized asphericity and acylindricity of the macro molecule. Interestingly, we also find that the dimensions of the side chains reveals differences in the distributions of side chain monomers by changing the backbone length Nb as the region between the two backbone-ends increases. A method to ext ract the persistence length of bottle-brush macromo lecules and its drawbacks is also discussed given that different measures of the persistence length are not mutually consistent with each other and depend distinctly both on Nb and the solvent quality.