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pH and Salt Response of Mixed Brushes Made of Oppositely Charged Polyelectrolytes Studied by in Situ AFM Force Measurements and Imaging
journal contribution
posted on 2018-04-09, 00:00 authored by Astrid Drechsler, Mahdy M. Elmahdy, Petra Uhlmann, Manfred StammThe response of mixed
brushes made of poly(acrylic acid) and poly(2-vinyl
pyridine) with a mixing ratio of about 60:40 was studied using atomic
force microscopy (AFM) force measurements with colloidal probes and
AFM imaging with a sharp tip in the pH range between 2.5 and 8 and
at varying KCl concentrations up to 1 M. It was found that under all
conditions a dense polyelectrolyte complex layer coexists with excess
polyelectrolyte chains in varying swelling states depending on pH
and salt concentration. The mixed brush thus combines typical features
of polyelectrolyte brushes and complexes. So, the increase of the
salt concentration not only led to a transition from osmotic to salted
brush regime but also to salt-induced softening or partial decomposition
of the complex layer. Attractive forces at high salt concentrations
indicated the presence of P2VP chains in the swollen layer even at
high pH values.