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Published on: May 15, 2017
Transient ordering in a quasi-two-dimensional liquid near freezing
Alice Shu-Yao Sheu1, Stuart Rice
1Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA.
The Journal of Chemical Physics
|July 8, 2008
Summary
This study explores ordered fluctuations in colloid fluids using molecular dynamics simulations. Results show how hexagonal and square symmetries emerge and dominate in dense liquids as wall separation changes, influencing freezing behavior.
Area of Science:
- Soft Matter Physics
- Colloid Science
- Computational Physics
Background:
- Understanding locally ordered fluctuations is key to characterizing the behavior of quasi-two-dimensional colloid fluids.
- These fluctuations influence phase transitions and the properties of confined liquids.
- Previous studies have explored fluid behavior, but the interplay of different ordered symmetries in confined systems requires further investigation.
Purpose of the Study:
- To theoretically investigate locally ordered fluctuations in quasi-two-dimensional colloid fluids confined between smooth hard walls.
- To analyze the emergence and dominance of hexagonal and square ordered fluctuations as a function of wall separation and density.
- To correlate observed fluctuation symmetries with the freezing behavior and resulting solid-state structures.
Main Methods:
- Molecular dynamics simulations of near hard spheres confined between smooth hard walls.
- Monitoring equilibrium fluctuations using the aperture cross-correlation function of scattered radiation.
- Analysis focused on single-time cross-correlated scattered radiation signals for systems with thicknesses less than two hard sphere diameters.
Main Results:
- For wall separations (H) between 1σ and 1.57σ, the fluid freezes into a single hexagonal layer, with hexagonal fluctuations extending into the liquid.
- Above H=1.57σ, hexagonal fluctuations persist up to H=1.75σ. Square ordered fluctuations emerge near freezing for H ≥ 1.57σ, becoming dominant as the system transitions to a two-layer square solid (H=1.8σ, 1.85σ).
- For H=1.9σ and 1.95σ, where a two-layer hexagonal solid forms, both square and hexagonal fluctuations are observed, with hexagonal symmetry appearing at lower densities and becoming more dominant with increasing density.
Conclusions:
- The symmetry of locally ordered fluctuations in confined colloid fluids is highly dependent on wall separation and density.
- Specific wall separations promote the dominance of either hexagonal or square fluctuations, directly preceding the formation of corresponding solid phases.
- The study reveals a complex interplay between fluctuation symmetries and freezing transitions, providing insights into the fundamental behavior of quasi-two-dimensional soft matter systems.
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