title: Molecular Interactions and Hydration States of Ultrathin Functional Films at the Solid-Liquid Interface.
abstract: We significantly improve the infrared analysis of ultrathin films in aqueous environments by employing in situ infrared ellipsometry. Combining it with rigorous optical modeling avoids otherwise typical misinterpretations of spectral features and enables the simultaneous quantification of chemical composition, hydration states, structure, and molecular interactions. We apply this approach to study covalently end-grafted, nanometer-thin brushes of poly(N-isopropylacrylamide), a thermoresponsive model polymer for proteins at solid-liquid interfaces. Quantitative analyses are based on a dielectric layer model that accounts for film swelling and deswelling, hydration of hydrophilic amide and hydrophobic isopropyl side groups, as well as molecular interactions of the polymer's amide moieties. We thereby quantify the hydration and structure dependence of intra- and intermolecular C═O···H-N and C═O···H2O hydrogen bonds, elucidating their role in the brush's temperature-induced phase separation. The presented method is directly applicable to functional and biorelated films like polymer and polypeptide layers, which is of topical interest for interface studies, such as membrane processes and protein unfolding.
authors.affiliation: Leibniz-Institut für Analytische Wissenschaften - ISAS - e.V. , Schwarzschildstraße 8, 12489 Berlin, Germany.
authors.forename: Andreas
authors.identifier: 0000-0002-5448-7956
authors.initials: A
authors.lastname: Furchner
authors.affiliation: Leibniz-Institut für Analytische Wissenschaften - ISAS - e.V. , Schwarzschildstraße 8, 12489 Berlin, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Kroning
authors.affiliation: Leibniz-Institut für Polymerforschung Dresden e.V. , Hohe Straße 6, 01069 Dresden, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Rauch
authors.affiliation: Leibniz-Institut für Polymerforschung Dresden e.V. , Hohe Straße 6, 01069 Dresden, Germany.
authors.forename: Petra
authors.identifier: 0000-0001-9298-4083
authors.initials: P
authors.lastname: Uhlmann
authors.affiliation: Leibniz-Institut für Polymerforschung Dresden e.V. , Hohe Straße 6, 01069 Dresden, Germany.
authors.forename: Klaus-Jochen
authors.initials: KJ
authors.lastname: Eichhorn
authors.affiliation: Leibniz-Institut für Analytische Wissenschaften - ISAS - e.V. , Schwarzschildstraße 8, 12489 Berlin, Germany.
authors.forename: Karsten
authors.initials: K
authors.lastname: Hinrichs