Avoidance model for soft particles. I. Charged spheres and rods beyond thedilute limit

The avoidance model introduced by Han and Herzfeld [Mater. Res. Soc. Symp. Proc. 463, 135 (1997)] for parallel, charged spherocylinders is extended to the case of charged spherocylinders with orientational freedom. The accura cy of the theory in the dilute solution limit is checked by comparing the p redicted second virial coefficient to exact values. For dilute charged sphe res, the avoidance model predictions are accurate to within 17% for all val ues of the charge and Debye-Huckel decay length. For dilute charged spheroc ylinders in the long rod limit, the theory is less accurate. The second vir ial coefficient is overestimated by 35%-90%. However, qualitative trends in the data are captured and smaller errors are expected for shorter rods or more concentrated solutions. Isotropic-nematic phase diagrams are presented for a range of ionic strengths, rod lengths, and charges. Specific compari son is made to experimental data for colloidal suspensions of tobacco-mosai c virus (TMV) particles and the bacteriophage fd. The concentration depende nce of the short range order is also discussed. (C) 1999 American Institute of Physics. [S0021-9606(99)52114-4].