Avoidance model for soft particles. I. Charged spheres and rods beyond the dilute 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 accuracy of the theory in the dilute solution limit is checked by comparing the predicted second virial coefficient to exact values. For dilute charged spheres, the avoidance model predictions are accurate to within 17% for all values of the charge and Debye-Huckel decay length. For dilute charged spherocylinders in the long rod limit, the theory is less accurate. The second virial 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 comparison is made to experimental data for colloidal suspensions of tobacco-mosaic virus (TMV) particles and the bacteriophage fd. The concentration dependence of the short range order is also discussed. (C) 1999 American Institute of Physics. [S0021-9606(99)52114-4].