ANGULAR-CORRELATIONS AND THE ISOTROPIC-NEMATIC PHASE-TRANSITION IN SUSPENSIONS OF TOBACCO MOSAIC-VIRUS

The specific magnetic-field-induced birefringence is measured in aqueo us suspensions composed of the charged rodlike particle tobacco mosaic vims (TMV) as a function of temperature, TMV concentration, ionic str ength, and TMV polydispersity over the entire isotropic range. This qu antity is proportional to the magnitude of the interparticle angular c orrelations at zero field. Theoretical expressions for the field-induc ed birefringence for both the mono- and polydisperse samples are deriv ed based on extensions of the Onsager model [L. Onsager, Ann. N.Y. Aca d. Sci. 51, 627 (1949)] and compare well with experiment. In addition, the isotropic-nematic phase coexistence concentrations are measured a s a function of ionic strength and temperature. The agreement between experiment and theory indicates that the TMV particles interact primar ily through electrostatic repulsion and that attractive forces are neg ligible.