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- ItemMelt-mixed PP/MWCNT composites: Influence of CNT incorporation strategy and matrix viscosity on filler dispersion and electrical resistivity(Basel : MDPI, 2019) Pötschke, Petra; Mothes, Fanny; Krause, Beate; Voit, BrigitteSmall-scale melt mixing was performed for composites based on polypropylene (PP) and 0.5–7.5 wt % multiwalled carbon nanotubes (MWCNT) to determine if masterbatch (MB) dilution is a more effective form of nanofiller dispersion than direct nanotube incorporation. The methods were compared using composites of five different PP types, each filled with 2 wt % MWCNTs. After the determination of the specific mechanical energy (SME) input in the MB dilution process, the direct-incorporation mixing time was adjusted to achieve comparable SME values. Interestingly, the electrical resistivity of MB-prepared samples with 2 wt % MWCNTs was higher than that of those prepared using direct incorporation—despite their better dispersion—suggesting more pronounced MWCNT shortening in the two-step procedure. In summary, this study on PP suggests that the masterbatch approach is suitable for the dispersion of MWCNTs and holds advantages in nanotube dispersion, albeit at the cost of slightly increased electrical resistivity.
- ItemPolypropylene-based melt mixed composites with singlewalled carbon nanotubes for thermoelectric applications: Switching from p-type to n-type by the addition of polyethylene glycol(Oxford : Elsevier Science, 2017) Luo, Jinji; Cerretti, Giacomo; Krause, Beate; Zhang, Long; Otto, Thomas; Jenschke, Wolfgang; Ullrich, Mathias; Tremel, Wolfgang; Voit, Brigitte; Pötschke, PetraThe thermoelectric properties of melt processed conductive nanocomposites consisting of an insulating polypropylene (PP) matrix filled with singlewalled carbon nanotubes (CNTs) and copper oxide (CuO) were evaluated. An easy and cheap route to switch p-type composites into n-type was developed by adding polyethylene glycol (PEG) during melt mixing. At the investigated CNT concentrations of 0.8 wt% and 2 wt% (each above the electrical percolation threshold of ∼0.1 wt%), and a fixed CuO content of 5 wt%, the PEG addition converted p-type composites (positive Seebeck coefficient (S)) into n-type (negative S). PEG was also found to improve the filler dispersion inside the matrix. Two composites were prepared: P-type polymer/CNT composites with high S (up to 45 μV/K), and n-type composites (with S up to −56 μV/K) through the addition of PEG. Two prototypes with 4 and 49 thermocouples of these p- and n-type composites were fabricated, and delivered an output voltage of 21 mV and 110 mV, respectively, at a temperature gradient of 70 K.
- ItemConjugated Polymers as a New Class of Dual-Mode Matrices for MALDI Mass Spectrometry and Imaging(Washington, DC : ACS Publications, 2018) Horatz, Kilian; Giampà, Marco; Karpov, Yevhen; Sahre, Karin; Bednarz, Hanna; Kiriy, Anton; Voit, Brigitte; Niehaus, Karsten; Hadjichristidis, Nikos; Michels, Dominik L.; Lissel, FranziskaMatrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) and MALDI MS imaging are ubiquitous analytical methods in medical, pharmaceutical, biological, and environmental research. Currently, there is a strong interest in the investigation of low molecular weight compounds (LMWCs), especially to trace and understand metabolic pathways, requiring the development of new matrix systems that have favorable optical properties and a high ionization efficiency and that are MALDI silent in the LMWC area. In this paper, five conjugated polymers, poly{[N,N'-bis(2-octyldodecyl)-naphtalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'(2,2'-bithiophene)} (PNDI(T2)), poly(3-dodecylthiophene-2,5-diyl) (P3DDT), poly{[2,3-bis(3-octyloxyphenyl)quinoxaline-5,8-diyl]-alt-(thiophene-2,5-diyl)} (PTQ1), poly{[N,N'-bis(2-octyldodecyl)-isoindigo-5,5'-diyl]-alt-5,5'(2,2'-bithiophene)} (PII(T2)), and poly(9,9-di-n-octylfluorenyl-2,7-diyl) (P9OFl) are investigated as matrices. The polymers have a strong optical absorption, are solution processable, and can be coated into thin films, allowing a vast reduction in the amount of matrix used. All investigated polymers function as matrices in both positive and negative mode MALDI, classifying them as rare dual-mode matrices, and show a very good analyte ionization ability in both modes. PNDI(T2), P3DDT, PTQ1, and PII(T2) are MALDI silent in the full measurement range (>m/z = 150k), except at high laser intensities. In MALDI MS experiments of single analytes and a complex biological sample, the performance of the polymers was found to be as good as two commonly used matrices (2,5-DHB for positive and 9AA for negative mode measurements). The detection limit of two standard analytes was determined as being below 164 pmol for reserpine and below 245 pmol for cholic acid. Additionally P3DDT was used successfully in first MALDI MS imaging experiments allowing the visualization of the tissue morphology of rat brain sections.
- ItemCopolymerization of zinc-activated isoindigo- and naphthalene-diimide based monomers: an efficient route to low bandgap π-conjugated random copolymers with tunable properties(Cambridge : RSC Publ., 2016) Karpov, Yevhen; Maiti, Jatindranath; Tkachov, Roman; Beryozkina, Tetyana; Bakulev, Vasiliy; Liu, Wei; Komber, Hartmut; Lappan, Uwe; Al-Hussein, Mahmoud; Stamm, Manfred; Voit, Brigitte; Kiriy, AntonThe present work aims at the extension of the scope of a recently discovered polycondensation of AB-type anion-radical monomers. To this end, we investigate the polymerization of isoindigo-based monomer and its copolymerization with the naphthalenediimide-based monomer. Although polycondensations of parent naphthalenediimide- and perylenediimide-based monomers involve chain-growth mechanism, we found that the corresponding isoindigo-based monomer polymerizes in a step-growth manner under the same reaction conditions. In contrast to Stille, Suzuki and direct arylation polycondensations which require prolonged stirring at high temperatures, the polymerization approach we employed in this study proceeds fast at room temperature. It was found that near statistical copolymerization of isoindigo-based anion-radical monomers with corresponding naphtalenediimide-based monomers proceeds smoothly resulting in a library of copolymers with varying composition and properties depending on the ratio of the monomers.
- ItemSugar-Modified Poly(propylene imine) Dendrimers Stimulate the NF-κB Pathway in a Myeloid Cell Line(Dordrecht [u.a.] : Springer Science + Business Media B.V, 2016) Jatczak-Pawlik, Izabela; Gorzkiewicz, Michal; Studzian, Maciej; Appelhans, Dietmar; Voit, Brigitte; Pulaski, Lukasz; Klajnert-Maculewicz, BarbaraPurpose: Fourth-generation poly(propylene imine) dendrimers fully surface-modified by maltose (dense shell, PPI-m DS) were shown to be biocompatible in cellular models, which is important for their application in drug delivery. We decided to verify also their inherent bioactivity, including immunomodulatory activity, for potential clinical applications. We tested their effects on the THP-1 monocytic cell line model of innate immunity effectors. Methods: To estimate the cytotoxicity of dendrimers the reasazurin assay was performed. The expression level of NF-κB targets: IGFBP3, TNFAIP3 and TNF was determined by quantitative real-time RT-PCR. Measurement of NF-κB p65 translocation from cytoplasm to nucleus was conducted with a high-content screening platform and binding of NF-κB to a consensus DNA probe was determined by electrophoretic mobility shift assay. The cytokine assay was performed to measure protein concentration of TNFalpha and IL-4. Results: We found that PPI-m DS did not impact THP-1 viability and growth even at high concentrations (up to 100 μM). They also did not induce expression of genes for important signaling pathways: Jak/STAT, Keap1/Nrf2 and ER stress. However, high concentrations of 4th generation PPI-m DS (25–100 μM), but not their 3rd generation counterparts, induced nuclear translocation of p65 NF-κB protein and its DNA-binding activity, leading to NF-κB-dependent increased expression of mRNA for NF-κB targets: IGFBP3, TNFAIP3 and TNF. However, no increase in pro-inflammatory cytokine secretion was detected. Conclusion: We conclude that maltose-modified PPI dendrimers of specific size could exert a modest immunomodulatory effect, which may be advantageous in clinical applications (e.g. adjuvant effect in anti-cancer vaccines).
- ItemFe3O4 Nanoparticles Grown on Cellulose/GO Hydrogels as Advanced Catalytic Materials for the Heterogeneous Fenton-like Reaction(Washington, DC : ACS Publications, 2019) Chen, Yian; Pötschke, Petra; Pionteck, Jürgen; Voit, Brigitte; Qi, HaisongCellulose/graphene oxide (GO)/iron oxide (Fe3O4) composites were prepared by coprecipitating iron salts onto cellulose/GO hydrogels in a basic solution. X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared, and X-ray diffraction characterization showed that Fe3O4 was successfully coated on GO sheets and cellulose. Cellulose/GO/Fe3O4 composites showed excellent catalytic activity by maintaining almost 98% of the removal of acid orange 7 (AO7) and showed stability over 20 consecutive cycles. This performance is attributable to the synergistic effect of Fe3O4 and GO during the heterogeneous Fenton-like reaction. Especially, the cellulose/GO/Fe3O4 composites preserve their activity by keeping the ratio of Fe3+/Fe2+ at 2 even after 20 catalysis cycles, which is supported by XPS analysis.
- ItemDispersability of multiwalled carbon nanotubes in polycarbonate-chloroform solutions(Oxford : Elsevier Science, 2014) Staudinger, Ulrike; Krause, Beate; Steinbach, Christine; Pötschke, Petra; Voit, BrigitteThe dispersion of commercial multiwalled carbon nanotubes (MWCNTs, Nanocyl™ NC7000) in chloroform and in polycarbonate (PC)-chloroform solutions was investigated by variation of the polymer concentration, MWCNT amount and sonication time and compared with PC/MWCNT composites, which were processed by melt mixing, subsequently dissolved in chloroform and dispersed via sonication under the same conditions. The sedimentation behaviour was characterised under centrifugal forces using a LUMiSizer® separation analyser. The space and time resolved extinction profiles as a measure of the stability of the dispersion and the particle size distribution were evaluated. Sonication up to 5 min gradually increases the amount of dispersed particles in the solutions. A significant improvement of the MWCNT dispersion in chloroform was achieved by the addition of PC indicating the mechanism of polymer chain wrapping around the MWCNTs. In dispersions of melt mixed PC/MWCNT composites the dispersion of MWCNTs is significantly enhanced already at a low sonication time of only 0.5 min due to very efficient polymer wrapping during the melt mixing process. However, the best dispersion quality does not lead to the highest electrical conductivity of thin composite films made of these PC/MWCNT dispersions.
- ItemDendritic glycopolymers based on dendritic polyamine scaffolds: view on their synthetic approaches, characteristics and potential for biomedical applications(London : Soc., 2014) Appelhans, Dietmar; Klajnert-Maculewicz, Barbara; Janaszewska, Anna; Lazniewska, Joanna; Voit, BrigitteIn this review we highlight the potential for biomedical applications of dendritic glycopolymers based on polyamine scaffolds. The complex interplay of the molecular characteristics of the dendritic architectures and their specific interactions with various (bio)molecules are elucidated with various examples. A special role of the individual sugar units attached to the dendritic scaffolds and their density is identified, which govern ionic and H-bond interactions, and biological targeting, but to a large extent are also responsible for the significantly reduced toxicity of the dendritic glycopolymers compared to their polyamine scaffolds. Thus, the application of dendritic glycopolymers in drug delivery systems for gene transfection but also as therapeutics in neurodegenerative diseases has great promise.
- ItemOrganic vapor sensing behavior of polycarbonate/polystyrene/multi-walled carbon nanotube blend composites with different microstructures(Amsterdam [u.a.] : Elsevier Science, 2019) Li, Yilong; Pionteck, Jürgen; Pötschke, Petra; Voit, BrigitteWith the focus on the use as leakage detectors, the vapor sensing behavior of conductive polymer composites (CPCs) based on polycarbonate/polystyrene/multi-walled carbon nanotube (PC/PS/MWCNT) blends with different blend ratios was studied as well as their morphological and electrical properties. In the melt mixed blend composites, the MWCNTs are preferentially localized in PC. At the PC/PS ratio of 70/30 wt%, the composites showed a sea-island structure, while for blends containing 40 wt% or 50 wt% PS co-continuous structures were developed resulting in a reduction in the MWCNT percolation threshold. The saturated vapors of the selected solvents have good interactions to PS but different interactions to PC. At 0.75 wt% MWCNT, sea-island CPCs showed high relative resistance change (Rrel) but poor reversibility towards moderate vapors like ethyl acetate and toluene, while CPCs with co-continuous structure exhibited lower Rrel and better reversibility. All CPCs showed poor reversibility towards vapor of the good solvent dichloromethane due to strong interactions between polymers and vapor. In the vapor of the poor solvent cyclohexane, CPCs with higher PS content showed increased Rrel. After extraction of the PS component by cyclohexane, the sensing response was decreased and the Rrel of the co-continuous blend even reached negative values.
- ItemReconstitution properties of biologically active polymersomes after cryogenic freezing and a freeze-drying process(London : RSC Publishing, 2018) Ccorahua, Robert; Moreno, Silvia; Gumz, Hannes; Sahre, Karin; Voit, Brigitte; Appelhans, DietmarReconstitution of biologically active polymersomes from the frozen or solid state into any fluid state is still a challenging issue for the design of new biological experiments and for the formulation of therapeutic agents. To gain knowledge about the reconstitution of pH-responsive and photo-crosslinked polymersomes, surface-functionalized and enzyme-containing polymersomers were cryogenically frozen (-20 °C) or freeze-dried with inulin as the lyoprotectant (0.1% w/v) and stored for a defined time period. Reconstituting those polymersomes in solution by thawing or a re-dispersing process revealed their original physical properties as well as their function as a pH-switchable enzymatic nanoreactor.