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Impact of single-particle compressibility on the fluid-solid phase transition for ionic microgel suspensions
M Pelaez-Fernandez1, Anton Souslov1, L A Lyon2
1School of Physics, Georgia Institute of Technology, 837 State Street, Atlanta, Georgia 30332, USA.
Physical Review Letters
|March 21, 2015
Summary
Ionic microgel suspensions show phase behavior influenced by particle stiffness. Osmotic pressure, dominated by free ions, allows volume fraction determination, revealing wider fluid-solid coexistence for stiffer, compressed microgels.
Area of Science:
- Soft matter physics
- Colloid science
- Polymer chemistry
Background:
- Ionic microgel suspensions are complex fluids with tunable properties.
- Understanding their phase behavior is crucial for applications in drug delivery and materials science.
- Particle stiffness significantly impacts suspension properties.
Purpose of the Study:
- To investigate the relationship between microgel particle stiffness and the phase behavior of ionic microgel suspensions.
- To determine the volume fraction of suspensions using osmotic pressure measurements.
- To analyze the influence of particle compression on fluid-solid phase coexistence.
Main Methods:
- Measurement of osmotic pressure (π) in ionic microgel suspensions.
- Determination of volume fraction (ϕ) from osmotic pressure data.
- Analysis of microgel particle volume as a function of volume fraction.
- Comparison of phase coexistence width with hard-sphere systems.
Main Results:
- Osmotic pressure is dominated by free ions and depends on volume fraction (ϕ).
- Volume fraction (ϕ) can be determined even for compressed microgel particles.
- Fluid-solid phase coexistence width is larger for stiffer microgels and decreases for softer ones.
- Soft microgels exhibit fluid-like behavior regardless of volume fraction.
- Phase coexistence width correlates with particle compression at coexistence volume fractions.
Conclusions:
- Ionic osmotic pressure is a reliable method for determining volume fraction in microgel suspensions.
- Microgel particle stiffness dictates the extent of fluid-solid phase coexistence.
- Particle compression plays a key role in the observed phase behavior of these systems.
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