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 bacteri ophage fd. Measurements were taken for concentrations spanning the entire c holesteric region at several ionic strengths and temperatures. In the limit of high ionic strength the cholesteric pitch (P-0) scales with concentrati on (c) as P-0 proportional to c(-1.66). As the ionic strength decreases, th e scaling exponent systematically changes to lower values.