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145 results on '"Niebuur, Bart‐Jan"'

1. Flow-induced anisotropy in a carbon black-filled silicone elastomer: electromechanical properties and structure

Author

Zimmer, Bettina, Niebuur, Bart-Jan, Schaefer, Florian, Coupette, Fabian, Tänzel, Victor, Schilling, Tanja, and Kraus, Tobias

Subjects
Condensed Matter - Materials Science
Abstract

Carbon black (CB)-elastomers can serve as low-cost, highly deformable sensor materials, but hardly any work exists on their structure-property relationships. We report on flow-induced anisotropy, considering CB-silicone films generated via doctor blade coating. Cured films showed slight electrical anisotropy, with conductivity parallel to the coating direction being lower than perpendicular to it. Furthermore, piezoresistive sensitivity was much larger for stretch perpendicular to the coating direction than for parallel stretch. Structural analysis for length scales up to the CB agglomerate level yielded only weak evidence of anisotropy. Based on this evidence and insight from CB network simulations, we hypothesize that shear flow during coating fragments the CB network and then induces a preferential aggregate alignment, as well as increased inter-particle distances, parallel to the coating direction. As a practical conclusion, already weak anisotropic structuration suffices to cause significant electric anisotropy.

Published
2024

5. PNIPAM Mesoglobules in Dependence on Pressure

Author

Niebuur, Bart-Jan, Pipich, Vitaliy, Appavou, Marie-Sousai, Mullapudi, Dharani, Nieth, Alec, Rende, Eric, Schulte, Alfons, and Papadakis, Christine M.

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) in aqueous solution forms mesoglobules above its cloud point temperature Tcp. While these are small and compact at atmospheric pressure, they are large and water-rich at high pressure. To identify the transition between these states, we employed optical microscopy and carried out isothermal pressure scans. Using very small angle neutron scattering, we determined the size and water content of the mesoglobules in pressure scans at different temperatures above Tcp. We observe a distinct transition at pressures of 35–55 MPa with the transition pressure depending on temperature. While the transition is smooth at high temperatures, i.e., far away from the coexistence line, it is abrupt at low temperatures, i.e., close to the coexistence line. Hence, at high temperatures, the swelling of the mesoglobules dominates, whereas at low temperatures, the coalescence of mesoglobules prevails. Subsequently decreasing the pressure results in a gradual deswelling of the mesoglobules at high temperature. In contrast, at low temperatures, small and compact mesoglobules form, but the large aggregates persist. We conclude that, on the time scale of the experiment, the disintegration of the large swollen aggregates into small and compact mesoglobules is only partially possible. Erasing the history by cooling the sample at the maximum pressure into the one-phase state does not result in qualitative changes for the behavior with the only difference that Fewer mesoglobules are formed when the pressure is decreased again. The newly identified transition line separates the low-pressure from the high-pressure regime.

Published
2024
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16. Crystalline Carbosilane‐Based Block Copolymers: Synthesis by Anionic Polymerization and Morphology Evaluation in the Bulk State

Author

Hübner, Hanna, Niebuur, Bart‐Jan, Janka, Oliver, Gemmer, Lea, Koch, Marcus, Kraus, Tobias, Kickelbick, Guido, Stühn, Bernd, Gallei, Markus, Hübner, Hanna, Niebuur, Bart‐Jan, Janka, Oliver, Gemmer, Lea, Koch, Marcus, Kraus, Tobias, Kickelbick, Guido, Stühn, Bernd, and Gallei, Markus

Abstract

Block copolymers (BCPs) in the bulk state are known to self‐assemble into different morphologies depending on their polymer segment ratio. For polymers with amorphous and crystalline BCP segments, the crystallization process can be influenced significantly by the corresponding bulk morphology. Herein, the synthesis of the amorphous‐crystalline BCP poly(dimethyl silacyclobutane)‐block‐poly(2vinyl pyridine), (PDMSB‐b‐P2VP), by living anionic polymerization is reported. Polymers with overall molar masses ranging from 17 400 g to 592 200 g mol⁻¹ and PDMSB contents of 4.8–83.9 vol% are synthesized and characterized by size‐exclusion chromatography and NMR spectroscopy. The bulk morphology of the obtained polymers is investigated by means of transmission electron microscopy and small angle X‐ray scattering, revealing a plethora of self‐assembled structures, providing confined and nonconfined conditions. Subsequently, the influence of the previously determined morphologies and their resulting confinement on the crystallinity and crystallization behavior of PDMSB is analyzed via differential scanning calorimetry and powder X‐ray diffraction. Here, fractionated crystallization and supercooling effects are observable as well as different diffraction patterns of the PDMSB crystallites for confined and nonconfined domains.

Published
2023

17. Self-Assembly of Polymer-Modified FePt Magnetic Nanoparticles and Block Copolymers

Author

Hartmann, Frank, Bitsch, Martin, Niebuur, Bart-Jan, Koch, Marcus, Kraus, Tobias, Dietz, Christian, Stark, Robert W., Everett, Christopher R., Müller-Buschbaum, Peter, Janka, Oliver, Gallei, Markus, Hartmann, Frank, Bitsch, Martin, Niebuur, Bart-Jan, Koch, Marcus, Kraus, Tobias, Dietz, Christian, Stark, Robert W., Everett, Christopher R., Müller-Buschbaum, Peter, Janka, Oliver, and Gallei, Markus

Abstract

The fabrication of nanocomposites containing magnetic nanoparticles is gaining interest as a model for application in small electronic devices. The self-assembly of block copolymers (BCPs) makes these materials ideal for use as a soft matrix to support the structural ordering of the nanoparticles. In this work, a high-molecular-weight polystyrene-b-poly(methyl methacrylate) block copolymer (PS-b-PMMA) was synthesized through anionic polymerization. The influence of the addition of different ratios of PMMA-coated FePt nanoparticles (NPs) on the self-assembled morphology was investigated using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The self-assembly of the NPs inside the PMMA phase at low particle concentrations was analyzed statistically, and the negative effect of higher particle ratios on the lamellar BCP morphology became visible. The placement of the NPs inside the PMMA phase was also compared to theoretical descriptions. The magnetic addressability of the FePt nanoparticles inside the nanocomposite films was finally analyzed using bimodal magnetic force microscopy and proved the magnetic nature of the nanoparticles inside the microphase-separated BCP films.

Published
2023

25. An Outer Membrane Vesicle‐Based Permeation Assay (OMPA) for Assessing Bacterial Bioavailability

Author

Richter, Robert, primary, Kamal, Mohamed A. M., additional, Koch, Marcus, additional, Niebuur, Bart‐Jan, additional, Huber, Anna‐Lena, additional, Goes, Adriely, additional, Volz, Carsten, additional, Vergalli, Julia, additional, Kraus, Tobias, additional, Müller, Rolf, additional, Schneider‐Daum, Nicole, additional, Fuhrmann, Gregor, additional, Pagès, Jean‐Marie, additional, and Lehr, Claus‐Michael, additional

Published
2021
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28. Highly Tunable Nanostructures in a Doubly pH‐Responsive Pentablock Terpolymer in Solution and in Thin Films

Author

Jung, Florian A., primary, Schart, Maximilian, additional, Bührend, Lukas, additional, Meidinger, Elisabeth, additional, Kang, Jia‐Jhen, additional, Niebuur, Bart‐Jan, additional, Ariaee, Sina, additional, Molodenskiy, Dmitry S., additional, Posselt, Dorthe, additional, Amenitsch, Heinz, additional, Tsitsilianis, Constantinos, additional, and Papadakis, Christine M., additional

Published
2021
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29. An Outer Membrane Vesicle-Based Permeation Assay (OMPA) for Assessing Bacterial Bioavailability

Author

Richter, Robert, Kamal, Mohamed A. M., Koch, Marcus, Niebuur, Bart-Jan, Huber, Anna-Lena, Goes Conceicao, Adriely, Volz, Carsten, Vergalli, Julia, Kraus, Tobias, Müller, Rolf, Schneider-Daum, Nicole, Fuhrmann, Gregor, Pagès, Jean-Marie, and Lehr, Claus-Michael

Subjects
in vitro studies, membrane permeation models, antimicrobial resistance, extracellular vesicles, bacterial bioavailability, drug optimization
Abstract

When searching for new antibiotics against Gram-negative bacterial infections, a better understanding of the permeability across the cell envelope and tools to discriminate high from low bacterial bioavailability compounds are urgently needed. Inspired by the phospholipid vesicle-based permeation assay (PVPA), which is designed to predict non-facilitated permeation across phospholipid membranes, outer membrane vesicles (OMVs) of Escherichia coli either enriched or deficient of porins are employed to coat filter supports for predicting drug uptake across the complex cell envelope. OMVs and the obtained in vitro model are structurally and functionally characterized using cryo-TEM, SEM, CLSM, SAXS, and light scattering techniques. In vitro permeability, obtained from the membrane model for a set of nine antibiotics, correlates with reported in bacterio accumulation data and allows to discriminate high from low accumulating antibiotics. In contrast, the correlation of the same data set generated by liposome-based comparator membranes is poor. This better correlation of the OMV-derived membranes points to the importance of hydrophilic membrane components, such as lipopolysaccharides and porins, since those features are lacking in liposomal comparator membranes. This approach can offer in the future a high throughput screening tool with high predictive capacity or can help to identify compound- and bacteria-specific passive uptake pathways.

Published
2021
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36. Thermoresponsive Polymere unter Hochdruck

Author

Niebuur, Bart-Jan, Papadakis, Christine M. (Prof., Ph.D.), and Hugenschmidt, Christoph P. (Prof. Dr.)

Subjects
Physik, Ingenieurwissenschaften, ddc:530, ddc:620
Abstract

This thesis investigates the phase behavior in aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions under pressure using neutron and light scattering techniques. The influence of pressure on the hydration state of PNIPAM and on the formation of the mesoglobules were studied in detail. Time-resolved investigations after rapid pressure jumps allowed the characterization of the growth kinetics of the mesoglobules. The effect of pressure on the co-nonsolvency behavior was investigated as well. In dieser Arbeit wird das Phasenverhalten in wässrigen Poly(N-isopropylacrylamid) (PNIPAM) Lösungen unter Hochdruck mit Neutronen- und Lichtstreumethoden untersucht. Der Einfluss von Druck auf den Hydratationszustand von PNIPAM und auf die Bildung der Aggregate wurden im Detail untersucht. Zeitaufgelöste Untersuchungen nach schnellen Drucksprüngen erlauben die Charakterisierung der Wachstumskinetik der Aggregate. Der Einfluss von Druck auf das Co-nonsolvency-Verhalten wurde ebenfalls untersucht.

Published
2019

38. Thermoresponsive polymers under high pressure

Author

Hugenschmidt, Christoph P. (Prof. Dr.), Papadakis, Christine M. (Prof., Ph.D.), Niebuur, Bart-Jan, Hugenschmidt, Christoph P. (Prof. Dr.), Papadakis, Christine M. (Prof., Ph.D.), and Niebuur, Bart-Jan

Abstract

This thesis investigates the phase behavior in aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions under pressure using neutron and light scattering techniques. The influence of pressure on the hydration state of PNIPAM and on the formation of the mesoglobules were studied in detail. Time-resolved investigations after rapid pressure jumps allowed the characterization of the growth kinetics of the mesoglobules. The effect of pressure on the co-nonsolvency behavior was investigated as well., In dieser Arbeit wird das Phasenverhalten in wässrigen Poly(N-isopropylacrylamid) (PNIPAM) Lösungen unter Hochdruck mit Neutronen- und Lichtstreumethoden untersucht. Der Einfluss von Druck auf den Hydratationszustand von PNIPAM und auf die Bildung der Aggregate wurden im Detail untersucht. Zeitaufgelöste Untersuchungen nach schnellen Drucksprüngen erlauben die Charakterisierung der Wachstumskinetik der Aggregate. Der Einfluss von Druck auf das Co-nonsolvency-Verhalten wurde ebenfalls untersucht.

Published
2019

39. Thermoresponsive polymers under high pressure

Author

Papadakis, Christine M. (Prof., Ph.D.), Papadakis, Christine M. (Prof., Ph.D.);Hugenschmidt, Christoph P. (Prof. Dr.), Niebuur, Bart-Jan, Papadakis, Christine M. (Prof., Ph.D.), Papadakis, Christine M. (Prof., Ph.D.);Hugenschmidt, Christoph P. (Prof. Dr.), and Niebuur, Bart-Jan

Abstract

This thesis investigates the phase behavior in aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions under pressure using neutron and light scattering techniques. The influence of pressure on the hydration state of PNIPAM and on the formation of the mesoglobules were studied in detail. Time-resolved investigations after rapid pressure jumps allowed the characterization of the growth kinetics of the mesoglobules. The effect of pressure on the co-nonsolvency behavior was investigated as well., In dieser Arbeit wird das Phasenverhalten in wässrigen Poly(N-isopropylacrylamid) (PNIPAM) Lösungen unter Hochdruck mit Neutronen- und Lichtstreumethoden untersucht. Der Einfluss von Druck auf den Hydratationszustand von PNIPAM und auf die Bildung der Aggregate wurden im Detail untersucht. Zeitaufgelöste Untersuchungen nach schnellen Drucksprüngen erlauben die Charakterisierung der Wachstumskinetik der Aggregate. Der Einfluss von Druck auf das Co-nonsolvency-Verhalten wurde ebenfalls untersucht.

Published
2019

42. 'Schizophrenic' Micelles from Doubly Thermoresponsive Polysulfobetaine‑b‑poly(N‑isopropylmethacrylamide) Diblock Copolymers

Author

Laschewsky, André, Vishnevetskaya, Natalya, Hildebrand, Viet, Niebuur, Bart-Jan, Grillo, Isabelle, Filippov, Sergey K., Mu&ller-Buschbaum, Peter, Papadakis, Christine M., and Publica

Subjects
smart materials, block copolymer, multiresponsive, polyzwitterion
Abstract

The 2-fold thermoresponsive diblock copolymer PSPP498-b-PNIPMAM144, which consists of a zwitterionic polysulfobetaine (PSPP) block and a nonionic poly(Nisopropylmethacrylamide) (PNIPMAM) block, is prepared by consecutive RAFT polymerizations. It combines the upper and lower critical solution temperature (UCST and LCST) behaviors, respectively, of the constitutive homopolymers in aqueous solution. We investigate the temperature-dependent phase behavior and the self-assembled structures of the block copolymer in D2O by turbidimetry and by small-angle neutron scattering (SANS) in salt-free solution and in the presence of small amounts of NaCl and NaBr. For comparison, solutions of PNIPMAM homopolymer in D2O are studied as well. Turbidimetry indicates thermally induced schizophrenic aggregation behavior for PSPP498-b-PNIPMAM144. SANS reveals that conventional star-like core−shell micellar structures are formed above the LCST transition, whereas below the UCST-transition, structure formation is much less pronounced. This is attributed to the different types of interactions, namely hydrophobic and ionic ones, dominating in the different regimes. Despite the increased polarity contrast between the zwitterionic and the nonionic blocks, and the much wider separation of the UCST- and LCST-based cloud points, CPUCST and CPLCST, the structural features of the new PSPP498-b-PNIPMAM144 resemble the ones found previously for the also 2-fold thermoresponsive analogue PSPP432-b-PNIPAM200, for which both phase transition temperatures nearly coincide. Remarkably, the addition of small amounts of NaBr or NaCl to the solution of PSPP498-b-PNIPMAM144 causes a significant increase of CPUCST, as well as minor but notable changes in the self−assembled structures, but no gross alterations of the phase behavior.

Published
2017

48. Aggregation behavior of doubly thermoresponsive polysulfobetaine‑b‑poly(N‑isopropylacrylamide) diblock copolymers

Author

Vishnevetskaya, Natalya S., Hildebrand, Viet, Niebuur, Bart-Jan, Grillo, Isabelle, Filippov, Sergey K., Laschewsky, André, Mu&ller-Buschbaum, Peter, Papadakis, Christine M., and Publica

Subjects
UCST, multiresponsive polymer, LCST, micelle, schizophrenic aggregation, block copolymer
Abstract

A 2-fold thermoresponsive diblock copolymer PSPP430-b-PNIPAM200 consisting of a zwitterionic polysulfobetaine (PSPP) block and a nonionic poly(N-isopropylacrylamide) (PNIPAM) block is prepared by successive RAFT polymerizations. In aqueous solution, the corresponding homopolymers PSPP and PNIPAM feature both upper and lower critical solution temperature (UCST and LCST) behavior, respectively. The diblock copolymer exhibits thermally induced schizophrenic aggregation behavior in aqueous solutions. Moreover, the ion sensitivity of the cloud point of the zwitterionic PSPP block to both the ionic strength and the nature of the salt offers the possibility to create switchable systems which respond sensitively to changes of the temperature and of the electrolyte type and concentra tion. The diblock copolymer solutions in D2O are investigated by means of turbidimetry and small-angle neutron scattering (SANS) with respect to the phase behavior and the self-assembled structures in dependence on temperature and electrolyte content. Marked differences of the aggregation below the UCST-type and above the LCST-type transition are observed. The addition of a small amount of NaBr (0.004 M) does not affect the overall behavior, and only the UCST-type transition and aggregate structures are slightly altered, reflecting the well-known ion sensitivity of the zwitterionic PSPP block.

Published
2016

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