Preparation and Investigation of Responsive Microgels in Flow Reactors

Fandrich P. Preparation and Investigation of Responsive Microgels in Flow Reactors. Bielefeld: Universität Bielefeld; 2022

Growth of Smart Microgels in a Flow Reactor Scrutinized by In-Line SAXS

Fandrich P, Vazquez J, Haverkamp R, Hellweg T. Growth of Smart Microgels in a Flow Reactor Scrutinized by In-Line SAXS. Langmuir. 2023

Effect of Methacrylic Acid in PNNPAM Microgels on the Catalytic Activity of Embedded Palladium Nanoparticles

Sabadasch V, Fandrich P, Annegarn M, Hellweg T. Effect of Methacrylic Acid in PNNPAM Microgels on the Catalytic Activity of Embedded Palladium Nanoparticles. Macromolecular Chemistry and Physics. 2022: 2200045

Multifunctional Core-Shell Microgels as Pd-Nanoparticle Containing Nanoreactors With Enhanced Catalytic Turnover

Sabadasch V, Dirksen M, Fandrich P, Hellweg T. Multifunctional Core-Shell Microgels as Pd-Nanoparticle Containing Nanoreactors With Enhanced Catalytic Turnover. Frontiers in chemistry. 2022;10: 889521.In this work, we present core-shell microgels with tailor-made architecture and properties for the incorporation of palladium nanoparticles. The microgel core consists of poly-N-isopropylacrylamide (PNIPAM) copolymerized with methacrylic acid (MAc) as anchor point for the incorporation of palladium nanoparticles. The microgel shell is prepared by copolymerization of NIPAM and the UV-sensitive comonomer 2-hydroxy-4-(methacryloyloxy)-benzophenone (HMABP). The obtained core-shell architecture was analyzed by means of photon correlation spectroscopy, while the incorporated amount of HMABP was further confirmed via Fourier transform infrared spectroscopy. Subsequently, the microgel system was used for loading with palladium nanoparticles and their size and localization were investigated by transmission electron microscopy. The catalytic activity of the monodisperse palladium nanoparticles was tested by reduction of 4-nitrophenol to 4-aminophenol. The obtained reaction rate constants for the core-shell system showed enhanced activity compared to the Pd-loaded bare core system. Furthermore, it was possible to recycle the catalyst several times. Analysis via transmission electron microscopy revealed, that the incorporated palladium nanoparticles emerged undamaged after the reaction and subsequent purification process since no aggregation or loss in size was observed. Copyright © 2022 Sabadasch, Dirksen, Fandrich and Hellweg

Acrylamide precipitation polymerization in a continuous flow reactor: an in situ FTIR study reveals kinetics

Fandrich P, Wiehemeier L, Dirksen M, Wrede O, Kottke T, Hellweg T. Acrylamide precipitation polymerization in a continuous flow reactor: an in situ FTIR study reveals kinetics. Colloid and Polymer Science. 2021;229(2):221-232.In this work, we present a combination of a continuous flow reactor with in situ monitoring of the monomer conversion in a precipitation polymerization. The flow reactor is equipped with a preheating area for the synthesis of thermoresponsive microgels, based on N-isopropylacrylamide (NIPAM). The reaction progress is monitored with in situ FTIR spectroscopy. The monomer conversion at defined residence times is determined from absorbance spectra of the reaction solutions by linear combination with reference spectra of the stock solution and the purified microgel. The reconstruction of the spectra appears to be in good agreement with experimental data in the range of 1710 to 1530 cm− 1, in which prominent absorption bands are used as probes for the monomer and the polymer. With increasing residence time, we observed a decrease in intensity of the ν(C=C) vibration, originating from the monomer, while the ν(C=O) vibration is shifted to higher frequencies by polymerization. Differences between the determined inline conversion kinetics and offline growth kinetics, determined by photon correlation spectroscopy (PCS), are discussed in terms of diffusion and point to a crucial role of mixing in precipitation polymerizations

Core-shell microgels synthesized in continuous flow: Deep insight into shell growth using temperature-dependent FTIR

Fandrich P, Annegarn M, Wiehemeier L, Ehring I, Kottke T, Hellweg T. Core-shell microgels synthesized in continuous flow: Deep insight into shell growth using temperature-dependent FTIR. Soft Matter. 2022.While core–shell microgels have been intensively studied in their fully synthesized state, the formation mechanism of the shell has not been completely understood. Such insight is decisive for a customization of microgel properties for applications. In this work, microgels based on a N-isopropylmethacrylamide (NiPMAM) core and a N-n-propylacrylamide (NnPAM) shell are synthesized in a continuous flow reactor. The shell growth is studied depending on the solution's time of residence inside the reactor. PCS experiments reveal a significant decrease of the volume phase transition temperatures of the core and the shell, with increasing residence time. At early stages, a decreased swelling capacity is found before a discrete NnPAM shell is formed. Temperature-dependent FTIR spectroscopy shows that the decreased swelling capacity originates from a pronounced interpenetrated network (IPN) between NnPAM and NiPMAM. AFM images resolve heterogeneously distributed shell material after 3 min, pointing to an aggregation of NnPAM domains before the distinct shell forms. The combination of diffusional properties, AFM images and vibrational information confirms a deeply interpenetrated network already at early stages of the precipitation polymerization, in which the shell material heavily influences the swelling properties

Pd Nanoparticle-Loaded Smart Microgel-Based Membranes as Reusable Catalysts

Sabadasch V, Dirksen M, Fandrich P, et al. Pd Nanoparticle-Loaded Smart Microgel-Based Membranes as Reusable Catalysts. ACS Applied Materials & Interfaces. 2022.In this work, palladium-loaded smart membranes made by UV cross-linking of thermoresponsive microgels are prepared to obtain a reusable, catalytically active material which can, for example, be implemented in chemical reactors. The membranes are examined with respect to their coverage of a supporting mesh via atomic force microscopy measurements. Force indentation mapping was performed in the dried, collapsed state and in the swollen state in water to determine the Young modulus. Furthermore, we compare the catalytic activity of the membrane with the corresponding suspended colloidal nanoparticle microgel hybrids. For this purpose, the reduction of 4-nitrophenol is an established model reaction to quantify the catalytic activity by UV–vis spectroscopy. The membrane is embedded inside a continuous stirred tank reactor equipped for continuous monitoring of the reaction progress. Although catalysis with membranes shows lower catalytic activity than freely dispersed particles, membranes allow straightforward separation and recycling of the catalyst. The fabricated membranes in this work show no decrease in catalytic activity between several cycles, unlike free particles. The feasible and durable deposition of catalytically active inter-cross-linked microgel particles on commercial nylon meshes as supporting scaffolds, as demonstrated in this work, is promising for up-scaling of continuous industrial processes

Doses of fluoride toothpaste for children up to 24 months

Abstract Aim The aim of this study was to test the dose of fluoride toothpaste by parents for their children aged up to 24 months. Methods Parents who use fluoride toothpastes for their children were asked to dose two commercially available toothpastes (A and B) with 1000 ppm fluoride each for their children as they would normally do at home. The toothpaste amounts were weighed, and as reference, the weight of an ‘optimal’ grain of rice-size amount of each toothpaste was used. Results 61 parents dosed a mean of 0.263 ± 0.172 g toothpaste A and 0.281 ± 0.145 g toothpaste B. The parents’ mean doses were 5.9 times higher for toothpaste A and 7.2 times higher for toothpaste B than an ‘optimal’ grain of rice-size amount (the reference dose as recommended). The difference between parent’s and reference dose was statistically significant (p < 0.001). Moreover, 39.3% of parents were not aware about conditions of use and warnings that have to be printed on the package of fluoride toothpastes. Conclusion In this study, parents significantly overdosed the toothpaste for their children. To avoid fluoride intake from toothpaste, parents can choose fluoride-free alternatives for the oral care of their infants and toddlers

Thermoresponsive Microgel-Based Free-Standing Membranes: Influence of Different Microgel Cross-Linkers on Membrane Function

Dirksen M, Fandrich P, Gött-Zink L, Cremer J, Anselmetti D, Hellweg T. Thermoresponsive Microgel-Based Free-Standing Membranes: Influence of Different Microgel Cross-Linkers on Membrane Function. Langmuir. 2022: acs.langmuir.1c02195

Stable DOPG/Glycyrrhizin Vesicles with a Wide Range of Mixing Ratios: Structure and Stability as Seen by Scattering Experiments and Cryo-TEM

Dargel C, Gräbitz-Bräuer F, Geisler R, et al. Stable DOPG/Glycyrrhizin Vesicles with a Wide Range of Mixing Ratios: Structure and Stability as Seen by Scattering Experiments and Cryo-TEM. Molecules. 2021;26(16): 4959.Phosphatidylglycerols represent a large share of the lipids in the plasmamembrane of procaryotes. Therefore, this study investigates the role of charged lipids in the plasma membrane with respect to the interaction of the antiviral saponin glycyrrhizin with such membranes. Glycyrrhizin is a natural triterpenic-based surfactant found in licorice. Vesicles made of 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1’-glycerol) (DOPG)/glycyrrhizin are characterized by small-angle scattering with neutrons and X-rays (SANS and SAXS). Small-angle scattering data are first evaluated by the model-independent modified Kratky–Porod method and afterwards fitted by a model describing the shape of small unilamellar vesicles (SUV) with an internal head-tail contrast. Complete miscibility of DOPG and glycyrrhizin was revealed even at a ratio of lipid:saponin of 1:1. Additional information about the chain-chain correlation distance of the lipid/saponin mixtures in the SUV structures is obtained from wide-angle X-ray scattering (WAXS)