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Item type:Publication, Access status: with files , The role of residual Hydrogen Peroxide for biological applications of polymeric N-oxides(Wiley, 2026-01-15); Polymers with N-oxide groups find applications in the biomedical field because they are highly hydrated in water, are considered to be nontoxic, and have stealth properties. Additional antimicrobial activity of polymeric N-oxides has also been reported, and it is currently unclear if this activity is a general feature of polymeric N-oxides or a special property of selected derivatives. N-Oxides are often prepared by oxidation of tertiary amines with hydrogen peroxide, which is notoriously difficult to remove from the resulting polymeric N-oxides. This study analyzes the role of residual oxidant in polymeric N-oxides for antimicrobial activity. Sensitive quantification reveals a significant release of hydrogen peroxide from oxidized polymers in solution and grafted on polyethylene or polyamide. The release of hydrogen peroxide from these polymers can lead to concentrations exceeding the minimum inhibitory concentrations (MICs) for Staphylococcus aureus and Escherichia coli. It can thus compromise microbiological assays. Rigorous removal of hydrogen peroxide leads to polymeric N-oxides with no antibacterial activity. Antibacterial effects of polymeric N-oxides against planktonic bacteria are primarily attributed to residual hydrogen peroxide, rather than to the intrinsic activity of the N-oxide functionality. Poly(N-oxide)-modified surfaces are therefore inert low-fouling materials with tunable, transient antibacterial functionality through controlled hydrogen peroxide release.Publicationtype: Journal Article18 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Load‐Induced Shear Band Formation in Microscale Epoxy Materials(Wiley, 2025-03-31); ; ; ; Thermosetting polymer thin films exhibit distinct mechanical behaviors at the microscopic scale compared to bulk materials. Experimental results reveal significant necking and unexpected shear band formation under tensile load. This study investigates the mechanisms underlying shear band formation in epoxy resin systems composed of bisphenol‐diglycidyl‐ether and diamines. Mechanical testing methods, including creep, relaxation, and cyclic testing, as well as ex situ and in situ high‐resolution infrared (IR) spectroscopy, are used synergistically with quantum mechanical calculations to elucidate the underlying molecular mechanisms. Additionally, molecular dynamics (MD) simulations on a nanoscale model explored the (visco‐)plastic behavior and network strain in epoxies. Our findings reveal a strong correlation between shear band formation and shifts in IR spectra, specifically the redshift of para‐phenylene and the blueshift of out‐of‐plane vibrations of aromatic moieties. These shifts are attributed to load‐induced aromatic stretching in the polymer backbone. The robust agreement between experimental data and simulation results supports these observations at both the atomic and nanoscale. These insights enhance the understanding of epoxy resin mechanics, potentially informing the design of advanced composite materials.Publicationtype: Journal Article104 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Performing Polarized Raman and Digital Image Correlation Analysis to Understand the Increased Ductility of Microscale Epoxy Materials(Wiley, 2025-03-27); ; ; ; The highly cross‐linked (epoxy) matrix material in fiber reinforced polymers has a microscopic volume between fibers and therefore exhibits different mechanical behavior in comparison to standard bulk epoxy samples. It has been found in previous studies that a decreased epoxy gauge volume leads to an increased deformation ability (necking and shear band formation). By using laser cutting to create dogbone samples from manufactured epoxy films, the gauge volume can be further reduced in comparison to previous studies, and the ductility can be enhanced even further. To understand load‐induced molecular mechanisms responsible for the increase in ductility at macroscale, this study combines digital image correlation (DIC) with tensile tests and precise force measurement. The global and local strains are calculated using the DIC data. The determined strains reach values up to 80% (global strains) and 120% (local strains), respectively. These strain values are significantly higher than those of archetypical brittle epoxy bulk samples (less than 10%). Polarized Raman spectra show that load‐bearing backbone molecules in the deformed film sample regions are oriented in the tensile load direction. This orientation might be due to the unraveling of entanglements, which can be seen as a sudden decrease followed by a subsequent rise in engineering stress values during deformation.Publicationtype: Journal Article38 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Synthesis of linear unsubstituted poly(4,4′-triphenylamine) via Suzuki-Miyaura coupling of an asymmetric AB monomer(2022-06-15); ; ; ; Polytriarylamines (PTAAs) are amorphous polymers that can be reversibly oxidized to generate stable radical cations. Despite exhibiting a low charge carrier mobility, PTAAs are widely used as hole-transporting layers in perovskite solar cells due to their excellent stability under ambient conditions. The highest occupied molecular orbital (HOMO) energy levels of PTAA are generally in the range of −5.1 to −5.2 eV, and therefore slightly too high for an optimal alignment with perovskites. Most linear PTAAs carry two or three methyl substituents per repeating unit. While these prevent crosslinking of chains and thus provide reaction control, the electron-donating substituents raise the energy level of the HOMO. Unsubstituted PTAA on the other hand is usually obtained crosslinked via oxidative polymerization, while nickel-catalyzed Grignard polycondensation leads to inclusion of impurities. We report the synthesis of linear unsubstituted PTAA using Suzuki-Miyaura coupling of a novel asymmetric monomer, 4-((4-bromophenyl)(phenyl)amino)phenyl)boronic acid M1. Based on matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) and 1H NMR analysis, we can conclude that the hydrogen-terminated linear polymer is obtained. The determined HOMO energy level of −5.47 eV is a favorable match for many perovskite systems.Publicationtype: Journal Article16