Single-Chain Conformational Characteristics of Comb-Like Polyelectrolytes: Molecular Dynamics Simulation Study

The single-chain conformation of a model comb polyelectrolyte, in which the electric charges are located on the last monomer of side chains, has been studied using molecular dynamics simulations. The model chain has a hydrophobic backbone and hydrophilic side chains. The influence of parameters such as the length of backbone and side chains, the grafting density of side chains, flexibility of the chain and different strengths of backbone hydrophobicity have been investigated. At high grafting density of side chains, a transition from turn to pearl-necklace and finally to globular conformation is observed by increasing the hydrophobicity. Radius of gyration (R-g) of the backbone depends linearly on the number of backbone monomers at low values of the backbone hydrophobicity, but at high values of the backbone hydrophobicity, because of the appearance of turn-like segments between successive globular sections in the pearl-necklace structure, the scaling exponent of R-g versus N is larger. Also, the chain flexibility affects the backbone conformation significantly. The increase of the persistence length leads to the appearance of the folded and then the extended conformations. In addition to the statistical properties of the chains, the investigation of the relaxation of the chains conformation shows that, the backbone takes almost its final conformation in the early time steps of the simulation for all conditions. It means that the relaxation time of the chain is relatively short (fast relaxation).