LCST Behavior of Lightly Charged Aqueous Polyelectrolytes
Numerous polymers of experimental interest, such as Poly(N-isopropylacrylamide) (PNIPAAm) and PEO, exhibit a lower critical solution temperature (LCST) in aqueous solution. A hydrogen-bonding lattice fluid (HBLF) model employing a combinatorial approach to the hydrogen bonds has previously provided a successful theoretical model for this behavior in the uncharged polymer/water two-component system. However, many systems of experimental interest, such as the human body, contain various electrolytes. The resulting presence of free charges in solution has been experimentally shown to have a significant effect on the LCST of the polymer-water system, presumably through interactions with hydrogen bonds. Furthermore, a common means of modulating the LCST of such systems is the incorporation of a low mole fraction of electrolytic groups into the chain backbone, yielding a lightly charged polyelectrolyte. The authors present an extension of the above HBLF model that addresses these issues by accounting for bound charges on the polymer chain and free charges in solution. The new model allows for the calculation of the LCST of ternary lightly charged polyelectrolyte systems such as Poly(N-isopropylacrylamide-co-acrylamide)-water-acid as a function of temperature, pressure, free salt concentration, pH, and polymer backbone charge concentration.
Simmons, David, "LCST Behavior of Lightly Charged Aqueous Polyelectrolytes" (2009). Polymer Engineering Faculty Research. 1358.