Quantifying Polyelectrolyte Complex Hydration

The mass of the systems in vials was weighed
at several points: empty, filled with all components, with the supernatant
removed, and dried. By comparing the mass of the systems with the
supernatant removed and when dried, we obtain the water content of
the PEC. Drying is verified via evaluation of the cobalt color; hydrated
wet cobalt is bright pink, while dehydrated cobalt is dark blue. Sufficient
cobalt was present after drying to visually verify successful dehydration.
The concentration of Co²⁺ ions in the supernatant phase
is determined using a Shimadzu 2401PC spectrophotometer via analysis
of the absorbance at a wavelength of 510 nm. The Co²⁺ concentrations
in the supernatant are compared to a polyelectrolyte-absent control
with the same initial CoCl₂ concentration. The partitioning
coefficient K_Co²⁺ is then determined
as where is the concentration of Co²⁺ in the supernatant, normalized for the polyelectrolyte-absent control C, which is defined as 100%. The mass of the hydrated complex
is m^pec, while m^sup is the mass of the supernatant. An assumption was made
that the density of (hydrated) PEC was approximately equal to that
of water.^{40 (link)}