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Amorphous to amorphous transition in particle rafts
Atul Varshney1, A Sane, Shankar Ghosh
1Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400-005, India.
Particle rafts exhibit a unique phase transition between amorphous states as particle density increases. This transition involves a shift from capillary bridging to frictional coupling, altering mechanical properties.
Area of Science:
- Soft matter physics
- Interfacial phenomena
- Colloidal science
Background:
- Particle rafts are space-filling assemblies of hydrophobic particles at air-water interfaces.
- These rafts can exist in different amorphous states depending on particle density.
Purpose of the Study:
- To investigate the phase transition of particle rafts between amorphous states.
- To characterize the structural and mechanical changes during this transition.
Main Methods:
- Simultaneous direct imaging and mechanical response measurements (longitudinal and shear stresses).
- Analysis of structural parameters: mean coordination number, Voronoi cell area, and displacement field.
- Investigating the role of capillary bridging and frictional coupling.
Main Results:
- A phase transition occurs between a low-density 'less-rigid' (capillary bridged) state and a high-density 'more-rigid' (frictionally coupled) state.
- The transition is marked by a subtle structural anomaly and a weakening of the shear response.
- Weakened shear response is linked to local plastic instabilities and depinning of the fluid contact line.
Conclusions:
- Particle rafts display an unusual amorphous-amorphous phase transition driven by particle density.
- The transition involves a change in inter-particle interactions from capillary bridging to frictional coupling.
- Understanding this transition offers insights into the mechanics of interfacial particle assemblies.
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