Crosspolarization with imperfect infrared polarizers

The analysis of vibrational bands is a core application of infrared (IR) spectroscopy. Polarization-dependent measurements enable the study of anisotropic materials. However, imperfect IR polarizers exhibit polarizer leakage, which causes pronounced bandshape and baseline distortions for samples with weak optical anisotropy. Based on the 4 × 4 Mueller-matrix formalism, we propose a polarimetric measurement scheme for handling imperfect polarizers and source prepolarization that delivers correct co- and crosspolarized transmission and reflection IR spectra. The scheme is applied to a weakly anisotropic polypropylene sheet, resolving crosspolarized signatures as small as 5⋅10−5. We determine the polymer's direction-dependent complex refractive index in the vibrational fingerprint range

Spektroskopische Infrarotellipsometrie an funktionalen Polymerfilmen

Ziel der vorliegenden Arbeit ist die qualitative sowie quantitative Untersuchung funktionaler Polymerfilme und stimuli-responsiver Polymerbürsten mittels spektroskopischer Infrarotellipsometrie. Die Stärke dieser Messmethode ist in der Fähigkeit begründet, Molekülschwingungen organischer Dünnschichtsysteme an der Fest/Flüssig-Grenzfläche zu wässrigen Umgebungen in-situ zu vermessen und mittels optischer Schichtmodelle zu quantifizieren. Unter anderem geben diese Schwingungen Aufschluss über chemische Zusammensetzung, Struktur und Wechselwirkungen. Es ist somit erstmals möglich, verschiedene Polymer/Wasser- und Polymer/Polymer-Wechselwirkungen in temperatursensitiven Polymerfilmen und -bürsten ellipsometrisch zu identifizieren und erfolgreich, auf physikalischen Modellen basierend, zu quantifizieren. Des Weiteren wurde Infrarotellipsometrie bemüht, um Adsorptions- und Desorptionsprozesse von Proteinen an Polyelektrolytbürsten zu studieren. Komplementäre Messmethoden wie sichtbare Ellipsometrie und In-situ-Infrarotmikroskopie geben Aufschluss über zusätzliche Probeneigenschaften. Insbesondere erlauben es geometrische Überlegungen zum Streiflichtobjektiv erstmals, in-situ-infrarot-mikroskopische Messungen an Polymerdünnfilmen auf Metallen basierend auf denselben optischen Modellen auszuwerten, welche auch für Ellipsometrie genutzt werden. Dies gibt zusätzliche quantitative Einblicke in sich verändernde Wechselwirkungen bei Änderung der Umgebungsbedingungen, wie zum Beispiel Luftfeuchtigkeit.The aim of the present work is the qualitative as well as quantitative investigation of functional polymer films and stimuli-responsive polymer brushes by means of spectroscopic infrared ellipsometry. The strength of this method lies in its ability to measure molecular vibrations of organic thin-film systems in-situ at the solid–liquid interface to aqueous environments, and to quantify these vibrations with optical layer models. Among others, molecular vibrations give insights into chemical composition, structure, and interactions. For the first time, it was thus possible to ellipsometrically identify various polymer–water and polymer–polymer interactions in temperature-sensitive polymer films and brushes as well as to quantify these on the basis of physical models. Furthermore, infrared ellipsometry was employed for studying adsorption and desorption processes of proteins at polyelectrolyte brushes. Complementary methods like visible ellipsometry and in-situ infrared microscopy shed light on additional sample properties. In particular, geometric considerations with respect to the grazing-incidence objective allow one to evaluate in-situ infrared-microscopic measurements on polymer thin films on metal substrates based upon the same optical models as used for ellipsometry. This provides additional insights into changing interactions upon changes of environmental conditions like humidity

Probing carbonyl–water hydrogen-bond interactions in thin polyoxazoline brushes

Temperature-responsive oxazoline-based polymer brushes have gained increased attention as biocompatible surfaces. In aqueous environment, they can be tuned between hydrophilic and hydrophobic behavior triggered by a temperature stimulus. This transition is connected with changes in molecule–solvent interactions and results in a switching of the brushes between swollen and collapsed states. This work studies the temperature-dependent interactions between poly(2-oxazoline) brushes and water. In detail, thermoresponsive poly(2-cyclopropyl-2-oxazoline), nonresponsive hydrophilic poly(2-methyl-2-oxazoline), as well as a copolymer of the two were investigated with in situinfrared ellipsometry. Focus was put on interactions of the brushes’ carbonyl groups with water molecules. Different polymer–water interactions could be observed and assigned to hydrogen bonding between C=O groups and water molecules. The switching behavior of the brushes in the range of 20–45°C was identified by frequency shifts and intensity changes of the amide I band

Probing carbonyl–water hydrogen-bond interactions in thin polyoxazoline brushes

Temperature-responsive oxazoline-based polymer brushes have gained increased attention as biocompatible surfaces. In aqueous environment, they can be tuned between hydrophilic and hydrophobic behavior triggered by a temperature stimulus. This transition is connected with changes in molecule–solvent interactions and results in a switching of the brushes between swollen and collapsed states. This work studies the temperature-dependent interactions between poly(2-oxazoline) brushes and water. In detail, thermoresponsive poly(2-cyclopropyl-2-oxazoline), nonresponsive hydrophilic poly(2-methyl-2-oxazoline), as well as a copolymer of the two were investigated with in situinfrared ellipsometry. Focus was put on interactions of the brushes’ carbonyl groups with water molecules. Different polymer–water interactions could be observed and assigned to hydrogen bonding between C=O groups and water molecules. The switching behavior of the brushes in the range of 20–45°C was identified by frequency shifts and intensity changes of the amide I band

Probing carbonyl-water hydrogen-bond interactions in thin polyoxazoline brushes

Temperature-responsive oxazoline-based polymer brushes have gained increased attention as biocompatible surfaces. In aqueous environment, they can be tuned between hydrophilic and hydrophobic behavior triggered by a temperature stimulus. This transition is connected with changes in molecule–solvent interactions and results in a switching of the brushes between swollen and collapsed states. This work studies the temperature-dependent interactions between poly(2-oxazoline) brushes and water. In detail, thermoresponsive poly(2-cyclopropyl-2-oxazoline), nonresponsive hydrophilic poly(2-methyl-2-oxazoline), as well as a copolymer of the two were investigated with in situ infrared ellipsometry. Focus was put on interactions of the brushes' carbonyl groups with water molecules. Different polymer–water interactions could be observed and assigned to hydrogen bonding between C=O groups and water molecules. The switching behavior of the brushes in the range of 20–45 °C was identified by frequency shifts and intensity changes of the amide I band

Supramolecular Orientation in Anisotropic Assemblies by Infrared Nanopolarimetry

We report on the experimental characterization of anisotropic supramolecular assemblies by infrared (IR) nanopolarimetry. The presented IR absorption anisotropy imaging method simultaneously provides nanoscale-resolved insights into internal composition, intermolecular interactions, and supramolecular orientation in a label-free and noninvasive fashion. Our study of porphyrin aggregates demonstrates that their morphology can be correlated with stable J-type and metastable H-type stacking-induced anisotropic organization, revealing different oriented attachment growth mechanisms supported by theory. This analysis establishes the broad applicability of IR nanopolarimetric studies to supramolecular polymerization and biomolecular assemblies, opening up new routes in polymer science and macromolecular research

Mid‐infrared dual‐comb polarimetry of anisotropic samples

Abstract The mid‐infrared (mid‐IR) anisotropic optical response of a material probes vibrational fingerprints and absorption bands sensitive to order, structure, and direction‐dependent stimuli. Such anisotropic properties play a fundamental role in catalysis, optoelectronic, photonic, polymer and biomedical research and applications. Infrared dual‐comb polarimetry (IR‐DCP) is introduced as a powerful new spectroscopic method for the analysis of complex dielectric functions and anisotropic samples in the mid‐IR range. IR‐DCP enables novel hyperspectral and time‐resolved applications far beyond the technical possibilities of classical Fourier‐transform IR approaches. The method unravels structure–spectra relations at high spectral bandwidth up to 90 cm−1 and short integration times of 65 μs, with previously unattainable time resolutions for spectral IR polarimetric measurements for potential studies of noncyclic and irreversible processes. The polarimetric capabilities of IR‐DCP are demonstrated by investigating an anisotropic inhomogeneous freestanding nanofiber scaffold for neural tissue applications. Polarization sensitive multi‐angle dual‐comb transmission amplitude and absolute phase measurements (separately for ss‐, pp‐, ps‐, and sp‐polarized light) allow the in‐depth probing of the samples’ orientation‐dependent vibrational absorption properties. Mid‐IR anisotropies can quickly be identified by cross‐polarized IR‐DCP polarimetry. Key points A novel dual‐comb laser‐based technique is established for polarization‐dependent mid‐infrared spectroscopy. Independent measurements of spectral s‐ and p‐polarized transmission amplitudes and phases in the μs range. Visualization of the anisotropy of nanofiber scaffolds as used for neural tissue applications

Supramolecular Orientation in Anisotropic Assemblies by Infrared Nanopolarimetry

We report on the experimental characterization of anisotropic supramolecular assemblies by infrared (IR) nanopolarimetry. The presented IR absorption anisotropy imaging method simultaneously provides nanoscale-resolved insights into internal composition, intermolecular interactions, and supramolecular orientation in a label-free and noninvasive fashion. Our study of porphyrin aggregates demonstrates that their morphology can be correlated with stable J-type and metastable H-type stacking-induced anisotropic organization, revealing different oriented attachment growth mechanisms supported by theory. This analysis establishes the broad applicability of IR nanopolarimetric studies to supramolecular polymerization and biomolecular assemblies, opening up new routes in polymer science and macromolecular research

Supramolecular Orientation in Anisotropic Assemblies by Infrared Nanopolarimetry

We report on the experimental characterization of anisotropic supramolecular assemblies by infrared (IR) nanopolarimetry. The presented IR absorption anisotropy imaging method simultaneously provides nanoscale-resolved insights into internal composition, intermolecular interactions, and supramolecular orientation in a label-free and noninvasive fashion. Our study of porphyrin aggregates demonstrates that their morphology can be correlated with stable J-type and metastable H-type stacking-induced anisotropic organization, revealing different oriented attachment growth mechanisms supported by theory. This analysis establishes the broad applicability of IR nanopolarimetric studies to supramolecular polymerization and biomolecular assemblies, opening up new routes in polymer science and macromolecular research