Free Gibbs energy of association
Isothermal calorimetry titration
When separate component polyelectrolytes are mixed from the aqueous phase the first ion pairing removes the complex from bulk solution and it is therefore incorrect to refer to a “concentration” of the remainder of the polymer. The difference in association energy between Pols and Polc association is small – a polymer segment loses about 0.25 kT (~0.6 kJ) in configurational entropy on adsorption.
Obtaining crucial thermodynamic data for polyelectrolyte complexation by calorimetry is problematic due to the lack of heat evolved. While no data for PECs was provided in the earlier studies, modern ultrasensitive calorimetric techniques are capable of shedding some quantitative insight. For example, this figure shows the isothermal calorimetry titration (ITC, a technique commonly used to study the interaction of biological molecules) of poly(styrene sulfonate) (PSS) by poly(diallyldimethylammonium) (PDADMA).