Rc. Michel et Wf. Reed, New evidence of the nonequilibrium nature of the "slow modes" of diffusionin polyelectrolyte solutions, BIOPOLYMERS, 53(1), 2000, pp. 19-39
The time-dependent behavior of the dissolution of polyelectrolyte powders i
n pure water and moderate ionic strength aqueous solvent was monitored by f
lowing dissolving material through an online filter, and then through a mul
tiangle light scattering unit, a refractometer, and a capillary viscometer.
When the polyelectrolytes were dissolved in solutions of moderate ionic st
rength, their dissolution behavior was similar to that of neutral polymers.
When dissolved in pure water, however, there was consistently a small popu
lation of aggregates that appeared at the beginning of the dissolution proc
ess, which then rapidly diminished. For large pore filtration, the aggregat
es reached a final low level, and slowly disappeared over the span of many
days, whereas for small pore filtration the aggregates disappeared complete
ly over a scale of minutes. The real-time data, together with size exclusio
n chromatography analysis, shed light on previously unanswered questions co
ncerning the nonequilibrium nature of this small population of polyelectrol
yte aggregates in low ionic strength solutions, and its relation to the "ex
traordinary phase" of diffusion (or "slow modes "). Further evidence is als
o provided that both angular scattering maxima due to interpolyion correlat
ions and the maximum of reduced viscosity vs polyion concentration ("electr
oviscous" effect) at low ionic strength are equilibrium properties that are
unrelated to these aggregates. (C) 2000 John Wiley & Sons, Inc.