LIQUID-LIKE ORDER OF CHARGED RODLIKE PARTICLE SOLUTIONS

The structural order in the isotropic phase of charged rodlike TMV solutions (length L = 300 nm) has been investigated by static light scattering (SLS) and small-angle neutron scattering (SANS) experiments. We present measurements of the static structure factor S(q) as a function of the ionic strength over the concentration regimes c < c* and c > c* (c* = 1 particle/L3). SANS results in the semidilute regime c > c* show that strong interparticle correlations are present even at concentrations as high as 25c*, in contrast to results for hard-rod systems. The magnitudes of the correlations depend on both the macroion concentration and the Debye screening length k-1. As expected the position of the first maximum of S(q) is found to scale with concentration as q(max) approximately C1/3 below the overlap concentration c* but surprisingly to turn over to a c1/2 behavior above c*. With increasing salt, at constant macroion concentration a decrease in structure is observed and the first-maximum position q(max) is shifted to larger scattering vectors. In the absence of any adequate theory we compare our results to SLS measurements and HNC calculations of a spherical particle system. The influence of added salt on TMV solutions is examined by Monte Carlo simulations at c < c*.