Determination of polyelectrolyte pKa values using surface-to-air tension measurements

The determination of pK(a) values of acids can be done in a multitude of manners, ranging from the classic potentiometric titration to computationally. We envisioned that it would be possible to determine the pK(a) values of polyelectrolytes using surface tension measurements at the surface-to-air interface. When measuring surface tension at the surface-to-air interface of polyelectrolytes at differing solution pH values a classic sigmoidal curve was obtained with the inflection point being the pK(a) value of the polymer. The pK(a) value of PAA, PAH, PEI, PSS, and PMA were all obtained with this novel technique. We were also able to illustrate how both the polymer and salt concentration effects the surface tension at the surfaceto-air interface and thus the pK(a) values. This is the first reported study of using surface tension at the surface-to-air interface to determine pK(a) values of acids. (C) 2015 Elsevier B.V. All rights reserved.