ELECTRIC AND MAGNETIC-FIELD STUDIES ON RODLIKE FD-VIRUS SUSPENSIONS

The electrical and optical properties of rodlike fd-virus particles (L = 880 nm, D = 9 nm) are investigated by magnetic and electric birefri ngence experiments and supplemented by electric field light-scattering measurements. In aqueous suspension the fd-virus particles are negati vely charged and surrounded by diffuse counterion clouds. The examinat ions are performed at very low ionic strength (10(-6) M). Under these conditions a liquid crystalline phase already occurs at fd-partiele co ncentrations above 0.6 mg/mL. In magnetic fields the rodlike fd-virus is aligned parallel to the magnetic field due to its diamagnetic aniso tropy. Almost complete particle alignment in magnetic fields is obtain ed for liquid crystalline samples, and the saturation value of the bir efringence is determined. The application of electric fields results i n a polarization of the counterion clouds and a statistical orientatio n of the dispersed particles. In low electric fields Kerr behavior is found, providing the electric anisotropy Delta alpha(el) of a single r od. At higher electric fields the diffuse Debye cloud is partly stripp ed away and a complete particle orientation is hindered. Electric fiel d light-scattering investigations yield quantitatively the decrease of the electric anisotropy Delta alpha(el) in high electric fields.