Dynamic properties of molecular chains with variable stiffness

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Abstract
The dynamics of a free-draining chain of variable stiffness in a dilute solution is investigated. The chain is considered as a differentiable space curve with stretching and bending elasticity. Second moments, like the mean square end-to-end distance, the radius of gyration, and the pair correlation function of the equilibrium distribution exactly agree with those of the well-known Kratky–Porod wormlike chain. The equation of motion of the chain is derived and solved by a normal mode analysis. In the limit of a flexible chain the model exhibits the well-known Rouse dynamics, whereas in the rod limit the eigenfunctions correspond to bending motion only. In addition, the rotational motion in the latter limit is naturally obtained within the model. The relaxation times obtained by the model are compared with experimental transient birefringence and dynamic light scattering data. In addition, electric dichroism measurements are interpreted in terms of the model. All of these experiments are in good agreement with the theoretical predictions.

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