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Polymer-mediated melting in ultrasoft colloidal gels
E Stiakakis1, D Vlassopoulos, C N Likos
1FO.R.T.H, Institute of Electronic Structure and Laser, GR-71110 Heraklion, Crete, Greece.
Physical Review Letters
|November 22, 2002
Summary
Adding linear polymers to star polymer gels melts them by altering effective interactions. Very high linear chain weights can unexpectedly re-gel the system through bridging flocculation.
Area of Science:
- Polymer physics
- Soft matter science
- Materials science
Background:
- High-arm-number star polymers form physical gels in athermal solvents above a critical concentration.
- These gels are kinetically trapped states.
Purpose of the Study:
- To investigate the effect of adding linear polymer chains on star polymer gels.
- To understand the mechanism behind the gel-liquid transition induced by linear polymers.
Main Methods:
- Rheological measurements (modulus) were performed on star polymer gels with varying concentrations and molecular weights of added linear chains.
- Theoretical explanation based on effective interactions and star depletion.
Main Results:
- Addition of linear chains reduces the gel modulus, leading to a gel-liquid transition.
- A reentrant gelation phenomenon was observed at very high linear-chain molecular weights.
- The transition and reentrant gelation were explained by effective interactions, star depletion, and bridging flocculation.
Conclusions:
- Linear polymers can effectively destabilize and melt star polymer physical gels.
- Bridging flocculation provides an explanation for reentrant gelation in these systems, similar to colloidal dispersions.