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Vitrification and gelation in sticky spheres
C Patrick Royall1, Stephen R Williams2, Hajime Tanaka3
1HH Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.
The Journal of Chemical Physics
|February 3, 2018
Summary
Dynamically arrested states like gels and glasses are distinguished by new signatures. Gels form via spinodal decomposition at high densities, resulting in inhomogeneous structures, unlike continuous, homogeneous glass transitions.
Area of Science:
- Soft Matter Physics
- Colloidal Science
- Materials Science
Background:
- Glasses and gels represent dynamically arrested, disordered states of matter, crucial in various scientific fields.
- Distinguishing between gel and glass transitions, especially at high densities, has been a long-standing challenge.
- Previous theories proposed spinodal gelation via phase separation or percolation mechanisms for arrest.
Purpose of the Study:
- To identify distinct dynamical and structural signatures differentiating gel and glass transitions.
- To resolve the mechanism of gelation and clarify its occurrence at high densities.
- To understand the relationship between gelation and the attractive glass transition.
Main Methods:
- Determination of the phase diagram for a colloidal model system of hard and 'sticky' spheres.
- Analysis of dynamical and structural properties to identify transition signatures.
- Investigation of the role of percolation in controlling system dynamics.
Main Results:
- Spinodal decomposition confirmed as the gelation mechanism, refuting percolation-based theories.
- Gels can form at significantly higher densities (up to volume fraction ϕ = 0.59) than previously thought.
- High-density gels exhibit discontinuous transitions and inhomogeneous structures, contrasting with continuous, homogeneous glass transitions.
- Gelation interrupts the onset of the attractive glass transition in supercooled liquids.
Conclusions:
- Established clear thermodynamic, dynamic, and structural criteria to distinguish gelation from vitrification.
- Demonstrated that high-density gels, while structurally similar to glasses, possess unique transition characteristics.
- Provided a unified framework for understanding arrested states in soft matter systems.
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