Journal
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 10, Issue 17, Pages 5231-5236Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.9b01690
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Funding
- Clusters of Excellence The Hamburg Centre for Ultrafast Imaging of the Deutsche Forschungsgemeinschaft (DFG) [EXC 1074, 194651731, EXC 2056, 390715994]
- Clusters of Excellence Advanced Imaging of Matter of the Deutsche Forschungsgemeinschaft (DFG) [EXC 1074, 194651731, EXC 2056, 390715994]
- DOE BES [DE-AC02-06CH11357]
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We present the structure and dynamics of highly concentrated core-shell nanoparticles composed of a silica core and a poly(N-isoproylacrylamide) (PNIPAm) shell suspended in water. With X-ray photon correlation spectroscopy, we are able to follow dynamical changes over the volume phase transition of PNIPAm at LCST = 32 degrees C. On raising the temperature beyond LCST, the structural relaxation times continue to decrease. The effect is accompanied by a transition from stretched to compressed exponential shape of the intensity autocorrelation function. Upon further heating, we find a sudden slowing down for the particles in their collapsed state. The q dependence of the relaxation time shows an anomalous change from tau(c) proportional to q(-3) to tau(c) proportional to q(-1). Small angle X-ray scattering data evidence a temperature-induced transition from repulsive to attractive forces. Our results indicate a temperature-induced phase transition from a colloidal liquid with polymer-driven dynamics toward a colloidal gel.
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