Journal
GELS
Volume 3, Issue 3, Pages -Publisher
MDPI
DOI: 10.3390/gels3030034
Keywords
hydrogel; pNipam; core-shell particle; lower critical solution temperature (LCST); thermoresponsive
Categories
Funding
- Deutsche Forschungsgemeinschaft [1681, FI 1235/2-1]
- excellence cluster The Hamburg Centre for Ultrafast Imaging, Structure, Dynamics, and Control of Matter at the Atomic Scale of the DFG
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Core-shell microgels were synthesized via a free radical emulsion polymerization of thermoresponsive poly-(N-isopropyl acrylamide), pNipam, on the surface of silica nanoparticles. Pure pNipam microgels have a lower critical solution temperature (LCST) of about 32 degrees C. The LCST varies slightly with the crosslinker density used to stabilize the gel network. Including a silica core enhances the mechanical robustness. Here we show that by varying the concentration gradient of the crosslinker, the thermoresponsive behaviour of the core-shell microgels can be tuned. Three different temperature scenarios have been detected. First, the usual behaviour with a decrease in microgel size with increasing temperature exhibiting an LCST; second, an increase in microgel size with increasing temperature that resembles an upper critical solution temperature (UCST), and; third, a decrease with a subsequent increase of size reminiscent of the presence of both an LCST, and a UCST. However, since the chemical structure has not been changed, the LCST should only change slightly. Therefore we demonstrate how to tune the particle size independently of the LCST.
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