Angular correlations and the isotropic-nematic phase transition in suspensions of tobacco mosaic virus

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Abstract
The specific magnetic-field-induced birefringence is measured in aqueous suspensions composed of the charged rodlike particle tobacco mosaic virus (TMV) as a function of temperature, TMV concentration, ionic strength, and TMV polydispersity over the entire isotropic range. This quantity is proportional to the magnitude of the interparticle angular correlations at zero field. Theoretical expressions for the field-induced birefringence for both the mono- and polydisperse samples are derived based on extensions of the Onsager model [L. Onsager, Ann. N.Y. Acad. Sci. 51, 627 (1949)] and compare well with experiment. In addition, the isotropic-nematic phase coexistence concentrations are measured as a function of ionic strength and temperature. The agreement between experiment and theory indicates that the TMV particles interact primarily through electrostatic repulsion and that attractive forces are negligible.