Tuning the Size of Thermoresponsive Poly(N-Isopropyl Acrylamide) Grafted Silica Microgels

Nun, Nils; Grübel, Gerhard; Sheyfer, Dina; Fischer, Birgit; Hinrichs, Stephan; Schroer, Martin A.

doi:10.3390/gels3030034

Journal Article

PUBDB-2017-11540

Tuning the Size of Thermoresponsive Poly(N-Isopropyl Acrylamide) Grafted Silica Microgels

Nun, N. ; Hinrichs, S. ; Schroer, M. A.EMBL* ; Sheyfer, D. ; Grübel, G.DESY* ; Fischer, B. (Corresponding author)Extern*

2017
MDPI Basel

Gels 3(3), 34 (2017) [10.3390/gels3030034]

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Please use a persistent id in citations: doi:10.3390/gels3030034

Abstract: 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 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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