In situ infrared ellipsometric study of stimuli-responsive mixed polyelectrolyte brushes

The switching behavior of stimuli-responsive mixed polymer brushes (d = 11 nm) was monitored for the first time in liquid phase in situ by infrared spectroscopic ellipsometry (IRSE). IRSE is presented as a new, sensitive in situ tool for online analysis of chemical changes in a thin complex film at the solid/liquid interface. Responsive behavior (protonation and deprotonation reaction) of the poly(acrylic acid)/poly(2-vinylpyridine) (PAA-mix-P2VP) brush was probed in aqueous solutions with pH ranging from pH 2 to pH 10. Structural and chemical changes in a thin polymer brush layer were identified from the analysis of infrared ellipsometric tanPsi spectra during the variation of pH. Systematic change in pH confirmed the reversible switching behavior of the PAA-mix-P2VP brush between three different states: swollen P2VP and compact PAA chains at pH 2, a compact "P2VP...PAA" complex at pH 6.5, and swollen PAA and compact P2VP chains at pH 10.