Freeze-Fracture Imaging of Solutions of Ordered Rigid Rods

Abstract

Solutions of rigid rods display orientational and/or positional order at appropriate concentrations. Model systems of rigid rods are formed by Tobacco Mosaic Virus (TMV) in water or dilute salt solutions. In pure water, TMV particles are strongly negatively charged and electrostatic repulsion orders the virus into three-dimensional crystals with both orientational and positional order. When salt is added to the system, electrostatic repulsion is screened and the TMV particles lose much of their positional order, but retain their orientational order and form a nematic liquid crystal phase.The long and short-range order of TMV solutions is best studied using freeze- fracture replication TEM. Each virus, which is the equivalent of a single molecule in a normal crystal or liquid crystal, is easily visualized as a discrete particle (TMV are approximately 300 nm long and 18 nm in diameter).