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

In this work, a continuous flow setup for in situ investigation of microgel growth with small-angle X-ray scattering (SAXS) is established. Poly(N-n- propylacrylamide) (PNNPAM) and poly(N-isopropylacrylamide) (PNIPAM) microgels are synthesized in H2O at different residence times inside a continuous flow reactor. The microgels are investigated by in situ SAXS and ex situ photon correlation spectroscopy. The size of the microgels was found to be reproducible in independent experiments with run times of up to 7 h. Already the scattering curves of the microgels with a time of residence of 15 min show a well-defined form factor. Further analysis of the scattering profiles confirms the spherical shape of the microgels. At a residence time of 2 min, the scattering intensity is significantly lower corresponding to a smaller particle size. The experimental conditions remain constant over time, which is crucial for long-time experiments. The PNNPAM system is found to be more suitable for the flow reactor experiment with in-line SAXS as it shows less polymer deposition in the tubing and forms particles with lower polydispersity. The presented reactor is characterized by a compact design and offers a plug and-play setup close to the sample environment. This work paves the way for investigations of microgel growth at e.g. synchrotron Xray beamlines.

Automated summary

A continuous flow setup for in situ investigation of microgel growth using small-angle X-ray scattering (SAXS) is established in this work. Poly(N-n-propylacrylamide) (PNNPAM) and poly(N-isopropylacrylamide) (PNIPAM) microgels are synthesized in a continuous flow reactor and investigated using in situ SAXS and ex situ photon correlation spectroscopy. The size of the microgels is found to be reproducible in independent experiments, and the spherical shape of the microgels is confirmed through scattering analysis. The presented compact reactor offers a plug and-play setup close to the sample environment, paving the way for future investigations of microgel growth at synchrotron X-ray beamlines.