Dresden 2020 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 19: Focus: Soft Matter and Nanocomposites - New opportunities with advanced neutron sources II

CPP 19.4: Talk

Monday, March 16, 2020, 15:45–16:00, ZEU 222

Polyelectrolyte Multilayer Films from Mixtures of Polyanions: Different Composition in Film and Preparation Solution — •Annekatrin Sill, Antonia Weltmeyer, Peter Nestler, Malte Paßvogel, Sven Neuber, and Christiane A. Helm — University Greifswald, Institute of Physics, Germany

Polyelectrolyte multilayer films were prepared from polyanion PSS and polycation PDADMA in 0.1 M NaCl by sequential adsorption of oppositely charged polyelectrolytes. PSS consisted of binary mixtures of long deuterated PSSd (Mw(PSSd) = 80.8 kDa) and short protonated PSS (Mw(PSS) = 10.6 kDa). With neutron reflectivity, it was found that the mole fraction of long PSSd in the film exceeded the one in the deposition solution. Indeed, the film consisted of only PSSd if the mole fraction of PSSd in the deposition solution exceeded 5%. This observation can be explained by the adsorption kinetics which were studied with in-situ ellipsometry. Two mechanisms determined the film composition: (i) during PSS deposition, adsorption of short PSS was reversible while adsorption of long PSSd was irreversible; thus, the PSSd fraction increased with adsorption time; (ii) if short PSS was present, each polycation adsorption step was followed by slow desorption of polyelectrolyte complexes consisting of PDADMA and short PSS molecules. Short PSS is bound with fewer electrostatic monomer/monomer bonds to the film and can easier desorb, or form complexes with PDADMA. These studies show how to measure and control film composition when polydisperse polyelectrolyte solutions are used for film preparation.