Effect of grafting density of the side chains on spontaneous curvature and persistence length of two-dimensional comblike macromolecules.
We develop a theory that predicts the response of a two-dimensional (2D) comblike macromolecule (brush) to the bending which is accompanied by redistribution of the side chains with respect to the backbone. The brush is considered under poor solvent conditions, i.e., monomer units of the side chains and of the backbone attract each other. The line tension is explicitly taken into account. It is shown that densely grafted brushes (or brushes with long side chains) demonstrate spontaneous curvature. This curvature is induced by elasticity of the side chains: asymmetrically distributed side chains forming curved segments of the brush possess smaller elastic free energy than symmetrically distributed ones forming rectilinear segments of the brush. Sparsely grafted brushes (or brushes with short enough side chains) exhibit elastic response to the bending. In this case, a role of the elasticity of the side chains diminishes and main contributions to the elastic response of the brush come from the mixing entropy of the side chains and from the line tension. It is shown that persistence length of the sparsely grafted brushes lambda as a function of the number of segments in the side chain M can be approximated by a power function, lambda=const x M(alpha), with the exponent alpha<or=2. This persistence length is much smaller than that of the 2D brush with fixed distribution of the side chains. Our theoretical predictions are consistent with computer simulations.
Potemkin
Igor I
II
Physics Department, Moscow State University, Moscow 119992, Russian Federation. igor@polly.phys.msu.ru
Popov
Konstantin I
KI