Conformations of semiflexible charged chains: an extended bundle versus repulsive coils

We consider two interacting semiflexible charged chains of length L(c) under shape fluctuations, where the interplay of electric and mechanical properties is found to yield rigidity-sensitive charge modulation and interdistance-dependent persistence length ℓ(p). The resulting conformation is characterized by equilibrium force between the chains and their fractal dimensions. It turns out that ℓ(p) and L(c) emerge as critical factors to determine the force nature as well as chain shapes. We show that conformational fluctuations cause the repulsion of nonsteric origin, and its competition with charge fluctuation effects yields the interchain force modulated by the length scales and counterion valence. As a result, it is predicted that flexible short chains can be more strongly repulsive than rigid long chains, although they carry smaller amount of net charges.