Smectic Phase in a Colloidal Suspension of Semiflexible Virus Particles

Aqueous suspensions of micron-length, charged, semiflexible fd virus particles are studied experimentally in order to explore properties of the cholesteric-smectic phase transition in a system approximating flexible, hard rods. Through comparison of this system with (1) computer simulations of hard, rigid rods, (2) experiments on tobacco mosaic virus, a rigid, charged virus, and on pf1, a flexible, charged virus, and (3) with recent theories of the nematic-smectic transition in flexible rods, we argue that flexibility raises the volume fraction at the phase transition, lowers the ratio of the smectic periodicity to the contour length, and drives the transition first order.