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 tan¾ 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