ISOTROPIC-CHOLESTERIC PHASE-TRANSITION IN COLLOIDAL SUSPENSIONS OF FILAMENTOUS BACTERIOPHAGE-FD

The co-existence concentrations of the isotropic and cholesteric liqui d crystalline phases of the semi-flexible rod-like virus fd in aqueous suspension were measured as a function of ionic strength at room temp erature. At several ionic strengths the magnetic-field-induced birefri ngence, which is proportional to the number of particles in a correlat ion volume N-corr, was measured for fd concentrations spanning the ent ire isotropic region. From this data the limiting concentration of sta bility (spinodal) of the isotropic phase, rho, was obtained. The co-e xistence concentrations and rho versus ionic strength compare well wi th predictions based on the theory of Khokhlov and Semenov, modified t o include the effects of charge. A theoretical expression for the magn etic birefringence of persistent polymers was derived and agreed well with the data with the exception that N-corr at the isotropic to liqui d crystal transition was smaller than predicted.