ELECTRIC BIREFRINGENCE MEASUREMENTS IN AQUEOUS FD VIRUS SOLUTIONS

Aqueous solutions of rodlike fd virus particles (length l = 880 nm, diameter d = 9nm) are examined by the transient electric birefringence method. A special experimental setup is used, which allows a very sensitive variation of the screened Coulomb interaction between the particles. The birefringence signal is measured as a function of the virus particle concentration and the ionic strength of the solution. For low applied electric field strength it is demonstrated that anomalous birefringence is an effect of the steric and electrostatic interactions between the fd virus particles. It is shown that this behavior is correlated to a decrease of the rotational diffusion constant D(R). In the case of high ionic strength the deduced values of D(R) are in agreement with the theory of Teraoka and Hayakawa1 up to a concentration of 8c* (c* = 1 particle/length3 is the overlap concentration); at larger concentrations the values are significantly higher than predicted.