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

While coreshell 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 -isopropylmeth...

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Bibliographic Details
Published in:Soft matter 2022-07, Vol.18 (29), p.5492-551
Main Authors: Fandrich, Pascal, Annegarn, Marco, Wiehemeier, Lars, Ehring, Ina, Kottke, Tilman, Hellweg, Thomas
Format: Article
Language:English
Subjects:
Continuous flow
Fourier transforms
Infrared spectroscopy
Interpenetrating networks
Microgels
Phase transitions
Reactors
Shells
Swelling
Synthesis
Temperature dependence
Transition temperatures
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Summary:While coreshell 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. Coreshell microgels are synthesized in a continuous flow reactor to investigate the shell growth. An interpenetrated network is formed at an early stage of the synthesis.
ISSN:1744-683X
1744-6848
DOI:10.1039/d2sm00598k