Handbook of Size Exclusion Chromatography and Related ...

filter size, so large in fact that a logarithmic scale is used to show the peaks. In salt
water there is no peak at all, and the TDSLS and RI curves are virtually identical.
The data were interpreted in terms of a very small population of aggregates
that are present upon initial dissolution in pure water, and which very slowly
dissolve. Although the initial burst of aggregates dissolved mostly in minutes, the
residual amount of aggregates, seen by the higher level plateaus for the largest
filter, took several weeks to dissolve totally. This was the first kinetic
demonstration of the existence of aggregates and their tendency to dissolve, and
lends considerable strength to demonstrations made earlier that the puzzling “slow
modes” of diffusion in polyelectrolyte solutions at low ionic strength are due to
incompletely dissolved aggregates (63,64). Hence, the slow modes do not
represent an equilibrium property of such solutions. Others had interpreted the
slow modes in terms of ordering or other equilibrium phenomena, and had even
given the name “extraordinary regime” to solutions manifesting these modes (65).
3 EQUILIBRIUM CHARACTERIZATION OF
MULTICOMPONENT SOLUTIONS
While equilibrium characterization is not the main focus of this chapter, the timedependent
approach to monitoring allows significant strides in characterizing
equilibrium systems by providing a continuous, automatic record of behavior as
solution conditions are changed. This not only provides much more detailed data
than normally found, but also eliminates tedious manual solution preparations and
data gathering.
One of the pre-eminent approaches to equilibrium characterization is SEC,
the main topic of this book. Light-scattering and viscosity detectors have now been
in use for many years in conjunction with SEC (26,66), so that their use in that
context can now be termed “traditional,” even if many SEC users still lag in
obtaining and using the detectors.
We are interested, hence, in finding new applications of the basic ACM and
detector train. A strong feature of this approach is that gradients of multiple
components can be produced in time, allowing the equilibrium behavior along any
path in the composition space of components to be monitored. This is illustrated
by three separate examples: (1) a single component polymer system, (2) the effect
of simple electrolytes on polyelectrolytes, and (3) the complex association
properties of polymers and micelles.
Although the following experiments were performed using an ISCO 2360
programmable mixer, even simpler means of obtaining ACM can be used, because
an RI is used to obtain the polymer concentration at every point; that is, gravity
feed a stirred vessel containing polymer solution with pure solvent to dilute it
slowly, or use a syringe pump to dilute it.
© 2004 by Marcel Dekker, Inc.