Isotropic-cholesteric phase transition in colloidal suspensions of filamentous bacteriophagefd

The co-existence concentrations of the isotropic and cholesteric liquid crystalline phases of the semi-flexible rod-like virus fd in aqueous suspension were measured as a function of ionic strength at room temperature. At several ionic strengths the magnetic-field-induced birefringence, which is proportional to the number of particles in a correlation volume N corr, was measured for fd concentrations spanning the entire isotropic region. From this data the limiting concentration of stability (spinodal) of the isotropic phase, ρ*, was obtained. The co-existence concentrations and ρ* versus ionic strength compare well with predictions based on the theory of Khokhlov and Semenov, modified to include the effects of charge. A theoretical expression for the magnetic birefringence of persistent polymers was derived and agreed well with the data with the exception that N corr at the isotropic to liquid crystal transition was smaller than predicted.