Sub-diffusive dynamics and two-step yielding in dense thermo-responsive microgel glasses

Sub-diffusive dynamics and two-step yielding in dense thermo-responsive microgel glasses We have prepared dense colloidal suspensions of thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles with different volume fractions by subjecting the particles to different amounts of osmotic compression. Structural ordering and dynamics have been investigated using light scattering and yielding behaviour by oscillatory rheology. At room temperature, suspensions have found to exhibit a glassy state with the microgel particle size to be smaller than that determined under dilute conditions (i.e. deswelling of particles under osmotic compression). Quite interestingly, we observed (a) sub-diffusive mean square displacement (MSD) at short times and (b) two-step yielding (i.e. loss modulus, G″(ω), exhibiting two peaks as a function of shear strain amplitude, γ o ) in the glassy state. These findings are interpreted in terms of the overlap of dangling polymer chains between shells of the neighbouring PNIPAM microgel particles which are known to have a core-shell structure. At elevated temperatures, the two-step yielding behaviour of the glasses has been observed to change into a single-step yielding. With further increase in temperature, it has been found that PNIPAM microgel glasses melt into a liquid-like order and the behaviour of MSD changes from sub-diffusive to diffusive type. The results are discussed in light of those reported for attractive and repulsive colloidal glasses. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Colloid Polymer Science Springer Journals

Sub-diffusive dynamics and two-step yielding in dense thermo-responsive microgel glasses

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Publisher
Springer Berlin Heidelberg
Copyright
Copyright © 2017 by Springer-Verlag GmbH Germany
Subject
Chemistry; Polymer Sciences; Soft and Granular Matter, Complex Fluids and Microfluidics; Characterization and Evaluation of Materials; Physical Chemistry; Food Science; Nanotechnology and Microengineering
ISSN
0303-402X
eISSN
1435-1536
D.O.I.
10.1007/s00396-017-4142-5
Publisher site
See Article on Publisher Site

Abstract

We have prepared dense colloidal suspensions of thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles with different volume fractions by subjecting the particles to different amounts of osmotic compression. Structural ordering and dynamics have been investigated using light scattering and yielding behaviour by oscillatory rheology. At room temperature, suspensions have found to exhibit a glassy state with the microgel particle size to be smaller than that determined under dilute conditions (i.e. deswelling of particles under osmotic compression). Quite interestingly, we observed (a) sub-diffusive mean square displacement (MSD) at short times and (b) two-step yielding (i.e. loss modulus, G″(ω), exhibiting two peaks as a function of shear strain amplitude, γ o ) in the glassy state. These findings are interpreted in terms of the overlap of dangling polymer chains between shells of the neighbouring PNIPAM microgel particles which are known to have a core-shell structure. At elevated temperatures, the two-step yielding behaviour of the glasses has been observed to change into a single-step yielding. With further increase in temperature, it has been found that PNIPAM microgel glasses melt into a liquid-like order and the behaviour of MSD changes from sub-diffusive to diffusive type. The results are discussed in light of those reported for attractive and repulsive colloidal glasses.

Journal

Colloid Polymer ScienceSpringer Journals

Published: Jul 5, 2017

References

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