SKM 2021 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 3: Polymer Physics
CPP 3.2: Vortrag
Montag, 27. September 2021, 14:00–14:15, H3
Dissociation degree and pKa value of polyacid systems in solution and coatings determined by FTIR titration — Luise Wirth1,2, Birgit Urban1, Carolin Naas1,2, and •Martin Müller1,2 — 1Leibniz-Institut für Polymerforschung Dresden e.V., Department Functional Colloidal Materials, Hohe Str. 6, D-01069 Dresden, Germany — 2Technische Universität Dresden, Department Chemistry and Food Chemistry, D-01062 Dresden, Germany
Dissociation degree a and pKa of poly(acrylic acid) (PAA) and propionic acid (PA) 0.1 M solutions were determined by FTIR titration and potentiometric (POT) titration concept. Increasing subsequently the pH value from 2 to 12 by adding 1 M NaOH portions, FTIR spectra of PA and PAA show decrease of n(C=O) and increase of n(COO-) band due to carboxyl (COOH) and carboxylate (COO-) groups, respectively. From the respective normalized band integrals A, the dissociation degree aIR=ACOO-/(ACOOH+ACOO-) can be calculated. pH was plotted versus aIR and fitted by pH=pKa+B log(aIR/(1-aIR)) related to Henderson-Hasselbalch equation with fit parameters pKa and empirical cooperativity factor B. The slight pKa deviation found for FTIR and POT titration, the respective deviation between monomeric PA and polymeric PAA and the PAA molecular weight trend (PAA-2K, PAA-50K, PAA-450K) are discussed based on the known two-phase model of polyelectrolyte solutions including Gibbs-Donnan potential concept. Furthermore, aIR of PAA within consecutively adsorbed polycation/PAA multilayer coatings was determined by FTIR titration showing significant effect of the outermost polyelectrolyte layer.