Cholesteric phase in virus suspensions

We report measurements of the cholesteric pitch and twist elastic constant (K(22)) in monodisperse suspensions of the rodlike virus filamentous bacteriophage fd. Measurements were taken for concentrations spanning the entire cholesteric region at several ionic strengths and temperatures. In the limit of high ionic strength the cholesteric pitch (P(0)) scales with concentration (c) as P(0) proportional to c(-1.66). As the ionic strength decreases, the scaling exponent systematically changes to lower values.