Dynamic light scattering by aqueous solutions of rodlike fd-virus particles

Dynamic light scattering (DLS) measurements on aqueous solutions of rodlike fd-virus particles (length=880 nm, diameter=9 nm) below and above the overlap concentration c*=1 particle/length3 are reported. In samples with screened Coulomb interaction the short-time behavior of the time correlation functions does not show a significant concentration dependence, in contrast to samples at very low ionic strength (strong Coulomb interaction), where the short-time behavior is dominated by the static structure factor S(q). In this case S(q) derived by DLS methods, using an equation that has been proved for interacting spherical particles and weakly interacting rods, is in excellent agreement with S(q) determined by static light scattering (SLS) up to a particle concentration of about 5c*. Above significant deviations are found. At very low ionic strength the existence of a distinct very long tail in the time correlation function as previously reported can be confirmed, but the new experiments suggest that this is due to dust particles and aggregates and not to the interaction between the fd particles.