AGGREGATES AND OTHER PARTICLES AS THE ORIGIN OF THE EXTRAORDINARY DIFFUSIONAL PHASE IN POLYELECTROLYTE SOLUTIONS

The "extraordinary" diffusional phase (EP) at low ionic strength, and the conditions for its removability by filtration were investigated for dilute solutions of the following linear polyelectrolytes: poly(L-lysine), heparin, chondroitin-6-sulfate, hyaluronate, polystyrene sulfonate, and variably ionized polyacrylamide. The EP was not present for all the different types studied, and for heparin, for example, the phase was present only for samples from certain sources. In all cases the phase was removable by filtration through sufficiently small pore-size membranes. Once filtered, the EP remained absent for over one week. It is concluded that the extraordinary diffusional phase consists of fairly stable polyelectrolyte aggregates, and sometimes also includes other very small particulate impurities. These aggregates and other small particles are thought to be present, or at least nascent, in the dry polyelectrolyte material, so that their properties may depend critically on the manner in which such dry material is produced. Tests for "reversibility" of the EP by cycling between high and low C(s) by dialysis further confirm these conclusions. The evidence is thus against the EP representing any type of temporal aggregates or local ordering, at least for the linear polyelectrolytes studied in this work. Rather, due to the extremely feeble scattering of ordinary polyelectrolytes at low ionic strength, the weak scattering from residual aggregates and other particles, not removed by ordinary filtration and centrifugation procedures, give autocorrelable scattering signals with long decay times. The "loss" of the extraordinary phase as ionic strength increases appears to be due simply to the weak EP scattering signal getting buried in the sharply increasing scattering from the ordinary polyelectrolyte phase. Model calculations based on experimental data support this latter conclusion.