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- ItemCharge‐Compensated N‐Doped π ‐Conjugated Polymers: Toward both Thermodynamic Stability of N‐Doped States in Water and High Electron Conductivity(Weinheim : Wiley-VCH, 2022) Borrmann, Fabian; Tsuda, Takuya; Guskova, Olga; Kiriy, Nataliya; Hoffmann, Cedric; Neusser, David; Ludwigs, Sabine; Lappan, Uwe; Simon, Frank; Geisler, Martin; Debnath, Bipasha; Krupskaya, Yulia; Al‐Hussein, Mahmoud; Kiriy, AntonThe understanding and applications of electron-conducting π-conjugated polymers with naphtalene diimide (NDI) blocks show remarkable progress in recent years. Such polymers demonstrate a facilitated n-doping due to the strong electron deficiency of the main polymer chain and the presence of the positively charged side groups stabilizing a negative charge of the n-doped backbone. Here, the n-type conducting NDI polymer with enhanced stability of its n-doped states for prospective “in-water” applications is developed. A combined experimental–theoretical approach is used to identify critical features and parameters that control the doping and electron transport process. The facilitated polymer reduction ability and the thermodynamic stability in water are confirmed by electrochemical measurements and doping studies. This material also demonstrates a high conductivity of 10−2 S cm−1 under ambient conditions and 10−1 S cm−1 in vacuum. The modeling explains the stabilizing effects for various dopants. The simulations show a significant doping-induced “collapse” of the positively charged side chains on the core bearing a partial negative charge. This explains a decrease in the lamellar spacing observed in experiments. This study fundamentally enables a novel pathway for achieving both thermodynamic stability of the n-doped states in water and the high electron conductivity of polymers.
- ItemBioinspired Polydopamine Coating as an Adhesion Enhancer Between Paraffin Microcapsules and an Epoxy Matrix(Washington, DC : ACS Publications, 2020) Fredi, Giulia; Simon, Frank; Sychev, Dmitrii; Melnyk, Inga; Janke, Andreas; Scheffler, Christina; Zimmerer, CordeliaMicroencapsulated phase change materials (PCMs) are attracting increasing attention as functional fillers in polymer matrices, to produce smart thermoregulating composites for applications in thermal energy storage (TES) and thermal management. In a polymer composite, the filler–matrix interfacial adhesion plays a fundamental role in the thermomechanical properties. Hence, this work aims to modify the surface of commercial PCM microcapsules through the formation of a layer of polydopamine (PDA), a bioinspired polymer that is emerging as a powerful tool to functionalize chemically inert surfaces due to its versatility and great adhesive potential in many different materials. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) evidenced that after PDA coating, the surface roughness increased from 9 to 86 nm, which is beneficial, as it allows a further increase in the interfacial interaction by mechanical interlocking. Spectroscopic techniques allowed investigating the surface chemistry and identifying reactive functional groups of the PDA layer and highlighted that, unlike the uncoated microcapsules, the PDA layer is able to react with oxirane groups, thereby forming a covalent bond with the epoxy matrix. Hot-stage optical microscopy and differential scanning calorimetry (DSC) highlighted that the PDA modification does not hinder the melting/crystallization process of the paraffinic core. Finally, SEM micrographs of the cryofracture surface of epoxy composites containing neat or PDA-modified microcapsules clearly evidenced improved adhesion between the capsule shell and the epoxy matrix. These results showed that PDA is a suitable coating material with considerable potential for increasing the interfacial adhesion between an epoxy matrix and polymer microcapsules with low surface reactivity. This is remarkably important not only for this specific application but also for other classes of composite materials. Future studies will investigate how the deposition parameters affect the morphology, roughness, and thickness of the PDA layer and how the layer properties influence the capsule–matrix adhesion.
- ItemThe Localization Behavior of Different CNTs in PC/SAN Blends Containing a Reactive Component(Basel : MDPI, 2021-3-1) Gültner, Marén; Boldt, Regine; Formanek, Petr; Fischer, Dieter; Simon, Frank; Pötschke, PetraCo-continuous blend systems of polycarbonate (PC), poly(styrene-co-acrylonitrile) (SAN), commercial non-functionalized multi-walled carbon nanotubes (MWCNTs) or various types of commercial and laboratory functionalized single-walled carbon nanotubes (SWCNTs), and a reactive component (RC, N-phenylmaleimide styrene maleic anhydride copolymer) were melt compounded in one step in a microcompounder. The blend system is immiscible, while the RC is miscible with SAN and contains maleic anhydride groups that have the potential to reactively couple with functional groups on the surface of the nanotubes. The influence of the RC on the localization of MWCNTs and SWCNTs (0.5 wt.%) was investigated by transmission electron microscopy (TEM) and energy-filtered TEM. In PC/SAN blends without RC, MWCNTs are localized in the PC component. In contrast, in PC/SAN-RC, the MWCNTs localize in the SAN-RC component, depending on the RC concentration. By adjusting the MWCNT/RC ratio, the localization of the MWCNTs can be tuned. The SWCNTs behave differently compared to the MWCNTs in PC/SAN-RC blends and their localization occurs either only in the PC or in both blend components, depending on the type of the SWCNTs. CNT defect concentration and surface functionalities seem to be responsible for the localization differences.
- ItemBio-inspired deposition of electrochemically exfoliated graphene layers for electrical resistance heating applications(Bristol : IOP Publishing, 2020-12-4) Utech, Toni; Pötschke, Petra; Simon, Frank; Janke, Andreas; Kettner, Hannes; Paiva, Maria; Zimmerer, CordeliaElectrochemically exfoliated graphene (eeG) layers possess a variety of potential applications, e.g. as susceptor material for contactless induction heating in dynamic electro-magnetic fields, and as flexible and transparent electrode or resistivity heating elements. Spray coating of eeG dispersions was investigated in detail as a simple and fast method to deposit both, thin conducting layers and ring structures on polycarbonate substrates. The spray coating process was examined by systematic variation of dispersion concentration and volume applied to heated substrates. Properties of the obtained layers were characterized by UV-VIS spectroscopy, SEM and Confocal Scanning Microscopy. Electrical conductivity of eeG ring structures was measured using micro-four-point measurements. Modification of eeG with poly(dopamine) and post-thermal treatment yields in the reduction of the oxidized graphene proportion, an increase in electrical conductivity, and mechanical stabilization of the deposited thin layers. The chemical composition of modified eeG layer was analyzed via x-ray photoelectron spectroscopy pointing to the reductive behavior of poly(dopamine). Application oriented experiments demonstrate the direct electric current heating (Joule-Heating) effect of spray-coated eeG layers.
- ItemAntimicrobial Brushes on Titanium via “Grafting to” Using Phosphonic Acid/Pyridinium Containing Block Copolymers(Weinheim : Wiley-VCH GmbH, 2023) Methling, Rafael; Dückmann, Oliver; Simon, Frank; Wolf‐Brandstetter, Cornelia; Kuckling, DirkCoating medical implants with antibacterial polymers may prevent postoperative infections which are a common issue for conventional titanium implants and can even lead to implant failure. Easily applicable diblock copolymers are presented that form polymer brushes via “grafting to” mechanism on titanium and equip the modified material with antibacterial properties. The polymers carry quaternized pyridinium units to combat bacteria and phosphonic acid groups which allow the linear chains to be anchored to metal surfaces in a convenient coating process. The polymers are synthesized via reversible-addition-fragmentation-chain-transfer (RAFT) polymerization and postmodifications and are characterized using NMR spectroscopy and SEC. Low grafting densities are a major drawback of the “grafting to” approach compared to “grafting from”. Thus, the number of phosphonic acid groups in the anchor block are varied to investigate and optimize the surface binding. Modified titanium surfaces are examined regarding their composition, wetting behavior, streaming potential, and coating stability. Evaluation of the antimicrobial properties revealed reduced bacterial adhesion and biofilm formation for certain polymers, albeit the cell biocompatibility against human gingival fibroblasts is also impaired. The presented findings show the potential of easy-to-apply polymer coatings and aid in designing next-generation implant surface modifications.
- ItemPoly(3-hexylthiophene)s Functionalized with N-Heterocyclic Carbenes as Robust and Conductive Ligands for the Stabilization of Gold Nanoparticles(Weinheim : Wiley-VCH, 2020) Sun, Ningwei; Zhang, Shi-Tong; Simon, Frank; Steiner, Anja Maria; Schubert, Jonas; Du, Yixuan; Qiao, Zhi; Fery, Andreas; Lissel, FranziskaRecently, N-heterocyclic carbenes (NHCs) are explored as anchor groups to bind organic ligands to colloidal gold (i.e. gold nanoparticles, Au NPs), yet these efforts are confined to non-conjugated ligands so far—that is, focused solely on exploiting the stability aspect. Using NHCs to link Au NPs and electronically active organic components, for example, conjugated polymers (CPs), will allow capitalizing on both the stability as well as the inherent conductivity of the NHC anchors. Here, we report three types of Br-NHC-Au-X (X=Cl, Br) complexes, which, when used as starting points for Kumada polymerizations, yield regioregular poly(3-hexylthiophenes)-NHC-Au (P3HTs-NHC-Au) with narrow molecular weight distributions. The corresponding NPs are obtained via direct reduction and show excellent thermal as well as redox stability. The NHC anchors enable electron delocalization over the gold/CP interface, resulting in an improved electrochromic response behavior in comparison with P3HT-NHC-Au. © 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
- ItemSand/Polyethyleneimine Composites with Enhanced Sorption/Desorption Properties toward Pollutants(Basel : MDPI, 2022) Bucatariu, Florin; Petrila, Larisa-Maria; Zaharia, Marius-Mihai; Simon, Frank; Mihai, MarcelaThe direct deposition of polyethyleneimine (PEI), a weak polycation with a large content of amino groups, onto sand fractions with different sizes (F70, F100, F200, and F355), resulted in versatile core-shell sorbents for water cleaning. Herein, PEI and the weak polyanion poly(acrylic acid) (PAA) were directly precipitated as an nonstoichiometric polyelectrolyte complex ([PEI]:[PAA] = 2:1) onto a sand surface followed by cross-linking with glutaraldehyde (GA) at three molar ratios ([CHO]:[amine] = 1:10; 1:5; 1:1 = r). Non-crosslinked polyelectrolyte chains were washed out in strongly basic (pH 14) and acidic (pH 0) media. The sand/PEI-GA composites were evaluated to determine the organic shell stability using swelling experiments and X-ray photoelectron spectroscopy. The sorbed/desorbed amount of two model pollutants (copper ions and bromocresol green) in column experiments depended on the sand fraction size and cross-linking degree of the PEI shell. The maximum recorded values, after five loading/release cycles of pollutant species onto F70/PEI-GAr, F100/PEI-GAr, F200/PEI-GAr, and F355/PEI-GAr, were situated between the 0.7–5.5 mg Cu2+/mL column and 3.7–15 mg BCG/mL column. Sand/PEI-GAr composites could act as promising sorbents, low-cost and eco-friendly, which could be applied for water purification procedures.