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Updated: Apr 30, 2026
10:56
Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures
Published on: May 20, 2014
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Yielding behavior in colloidal glasses: comparison between "hard cage" and "soft cage"
Zhi Zhou1, Javoris V Hollingsworth, Song Hong
1State Key Laboratory of Polymer Physics and Chemistry, Joint Laboratory of Polymer Science and Materials, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
Summary
This study investigates yielding in polystyrene-poly(N-isopropylacrylamide) microgels. Results show yielding behavior transitions from hard sphere to soft jammed glass with changing shell/core ratios and volume fractions.
Area of Science:
- Materials Science
- Polymer Science
- Rheology
Background:
- Microgel systems composed of polystyrene (PS) core and poly(N-isopropylacrylamide) (PNIPAM) shell exhibit complex rheological properties.
- Understanding yielding behavior is crucial for predicting material response under stress.
Purpose of the Study:
- To investigate the yielding behavior of PS-PNIPAM core-shell microgel suspensions.
- To explore the influence of varying shell/core ratios and volume fractions on rheological response.
- To construct a yielding state diagram for these microgel systems.
Main Methods:
- Rheological measurements were performed on PS-PNIPAM microgel suspensions.
- Varying shell/core ratios (0.15, 0.34, 1.10) and volume fractions were studied.
- Analysis focused on the loss modulus (G″) to understand yielding mechanisms.
Main Results:
- A shell/core ratio of 0.15 showed hard sphere (HS) yielding with G″ peak decreasing with volume fraction.
- A shell/core ratio of 1.10 exhibited one-step yielding, with G″ peak increasing with volume fraction, indicating particle deformation.
- An intermediate ratio of 0.34 displayed two-step yielding, attributed to shell deformation and core-induced cage breaking, merging at high volume fractions.
Conclusions:
- The study demonstrates a transition in yielding behavior from HS to soft jammed glass.
- Shell deformation and core interactions significantly influence the yielding mechanisms of these microgels.
- A comprehensive yielding state diagram was established based on the observed behaviors.
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