Aqueous mixtures of spherical and rodlike (flexible) macroparticles: structure and dynamics of latex spheres in saltfree solutions

This paper resumes light scattering investigations of saltfree aqueous solu tions of two component mixtures of charged spheres by extending those measu rements to systems in which one component is replaced by essentially stiff rodlike particles. In a second step of investigations these were replaced b y linear flexible particles. Fd-virus particles (length l = 883 nm) or macr omolecules of NaPSS of four different contour lengths have been used as rep resentatives. Mostly the concentration of latex spheres was fixed at 0.02 V ol%. The concentration of the other component was varied over a wide range. Concerning the scattering intensity, the contribution of the latex spheres dominates, in particular in the systems containing NaPSS particles. This s implifies the interpretation of data considerably. A rearrangement of the s pheres is observed, depending on the shape of the other sort of particles. These conclusions can be drawn from the shift of measured static structure factor S-M(q) with concentration c. A power law is found for the q-value of the maximum. The exponent depends on the-properties of the second componen t. For the lower molecular weight (MW) samples of NaPSS below a critical co ncentration, the exponent is smaller than 1/3. decreasing the more the smal ler the MW of the samples is. A tentative explanation in terms of charge nu mber of NaPSS particles is given. The short time dynamics has been explored too. From the data a "dynamically determined structure factor" can be deri ved, that can be compared with the measured static structure factor. Good ( fd) and fair (NaPSS) agreement is obtained respectively. Only at small wave numbers below the maximum of S-M(q) deviations occur which increase with co ncentration; they are consistent with hydrodynamic interaction.