Anomalous Dynamics of Concentrated Silica-PNIPAm Nanogels

Lara Frenzel; Felix Lehmkühler; Irina Lokteva; Suresh Narayanan; Michael Sprung; Gerhard Grübel

doi:10.1021/acs.jpclett.9b01690

Anomalous Dynamics of Concentrated Silica-PNIPAm Nanogels

J Phys Chem Lett. 2019 Sep 5;10(17):5231-5236. doi: 10.1021/acs.jpclett.9b01690. Epub 2019 Aug 23.

Authors

Lara Frenzel^{1

2}, Felix Lehmkühler^{1

2}, Irina Lokteva^{1

2}, Suresh Narayanan³, Michael Sprung¹, Gerhard Grübel^{1

2}

Affiliations

¹ Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607 Hamburg, Germany.
² The Hamburg Centre for Ultrafast Imaging (CUI), Luruper Chaussee 149, 22761 Hamburg, Germany.
³ Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States.

PMID: 31433650
DOI: 10.1021/acs.jpclett.9b01690

Abstract

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 °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 τ_c ∝ q^-3 to τ_c ∝ 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.