Helix--rod transition in a nanospring.

A model of helical spring is described whose effective pitch and length are decided by the balance of the attractive van der Waals and repulsive hydration and electrical double layer forces. Also the electric contribution to the curvature free energy is taken into account. The stability of the nanospring is investigated and it is shown that the spring becomes unstable and jumps to its extended state on increase of electrostatic repulsion beyond a limit implying a jump in viscosity of suspension of springs in the solution. The magnitude of the jump and threshold potential are investigated.