Nanoscopic visualization of cross-linking density in polymer networks with diarylethene photoswitches

The in situ nanoscopic imaging of soft matter polymer structures is of paramount importance to gain a detailed knowledge of the relationship between structure, properties and functionality on the nanoscopic scale. Cross‐linking of polymer chains has tremendous effects on the viscoelastic properties of gels, and the correlation of mechanic properties on the distribution and amount of cross‐linkers is of huge relevance for applications as well as for a detailed understanding of polymers on the molecular scale. We introduce a super‐resolution fluorescence microscopy based methodology enabling the visualization and quantification of cross‐linker points in polymer systems. A novel diarylethene‐based photoswitch with a highly fluorescent closed and a non‐fluorescent open form is used as a photoswitchable cross‐linker in a polymer network. Its photophysical properties, switching behaviour, and high photostability make the dye an ideal candidate for photoactivation localization microscopy (PALM) without further modification of the structure of interest. As an example for its capability to nanoscopically visualize cross‐linking, we investigate pNIPAM microgels as system known with variations in internal cross‐linking density.publishe

Nihon ni okeru enkaku shinryo bijinesu no arikata : Amerika kigyo tono hikaku kara kosatsusuru

To realize carriers for drug delivery, cationic containers are required for anionic guests. Nevertheless, the toxicity of cationic carriers limits their practical use. In this study, we investigate a model system of polyampholyte N-isopropylacrylamide (NIPAM)-based microgels with a cationic core and an anionic shell to study whether the presence of a negative shell allows the cationic core to be shielded while still enabling the uptake and release of the anionic guest polyelectrolytes. These microgels are loaded with polystyrene sulfonate of different molecular weights to investigate the influence of their chain length on the uptake and release process. By means of small-angle neutron scattering, we evaluate the spatial distribution of polystyrene sulfonate within the microgels. The guest molecules are located in different parts of the core–shell microgels depending on their size. By combining these scattering results with UV-vis spectroscopy, electrophoretic mobility and potentiometric titrations we gain complementary results to investigate the uptake and release process of polyelectrolytes in polyampholyte core–shell microgels. Moreover, Brownian molecular dynamic simulations are performed to compare the experimental and theoretical results of this model. Our findings demonstrate that the presence of a shell still enables efficient uptake of guest molecules into the cationic core. These anionic guest molecules can be released through an anionic shell. Furthermore, the presence of a shell enhances the stability of the microgel–polyelectrolyte complexes with respect to the cationic precursor microgel alone

Synthesis of Polyampholyte Janus-like Microgels by Coacervation of Reactive Precursors in Precipitation Polymerization

Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli-responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus-like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self-assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus-like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA