Twist and writhe dynamics of stiff polymers.

I consider the dynamics of a stiff filament, in particular the coupling of twist and bend via writhe. The time dependence of the writhe of a filament of length L is ([Wr(t) - Wr(0)]2) > approximately Lt(1/4). Simulations, on a simple model of a stiff polymer, are used to confirm scaling arguments. Fuller's theorem, and its relation with geometric phases, is reconsidered for open filaments.