Shear clustering in solution: Polyelectrolytes compared to uncharged polymers

Abstract

The number Σ of polymer molecules that flow together in a cluster at the crossover concentration (separating the solvent-dominated from the polymer-dominated regime) is for a given mass of the solutes in the case of polyelectrolytes by two to three orders of magnitude smaller than for uncharged polymers. According to the present analysis, this difference is attributed to the ability of polyelectrolytes to form ordered structures even at very small concentrations. The cluster size at the crossover concentration varies in large limits from system to system. This observation can be rationalized by the fact that the crossover concentration is primarily given by static properties of the polymers in contrast to the cluster size, for which interactions are decisive. At sufficiently high dilution, the number of macromolecules flowing together as a function of their concentration c (mass/volume) obeys the following relationship: Σ = Ksystem + log c, where the constant characterizes the system.