Two-dimensional fluid with competing interactions exhibiting microphase separation: theory for bulk and interfacial...

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Statistical Mechanics

Background:

• Two-dimensional (2D) fluids confined to interfaces, like the air-water interface, exhibit complex self-assembly behaviors.
• These systems often display spontaneous formation of cluster and stripe morphologies due to competing interactions between colloidal particles.

Purpose of the Study:

• To develop a simple density functional theory (DFT) for modeling 2D colloidal fluids with competing interactions.
• To predict the phase diagram and structural properties of these 2D systems.
• To investigate the effects of confinement on the behavior of 2D colloidal fluids.

Main Methods:

• Development of a density functional theory model for 2D colloidal dispersions.
• Theoretical prediction of bulk phase diagrams, including modulated phases.
• Comparison of theoretical predictions with existing simulation data.
• Derivation of approximate expressions for the static structure factor and modulation length scales.
• Analysis of fluid behavior under confinement between parallel hard walls.

Main Results:

• The DFT successfully predicts a phase diagram featuring homogeneous fluid, cluster, stripe, and bubble modulated phases.
• Theoretical predictions show qualitative agreement with literature simulation results for the model system.
• The theory provides insights into the fluid structure and allows for calculation of key parameters like the static structure factor.
• Complex phase behavior is observed for the 2D fluid under confinement.

Conclusions:

• The developed density functional theory offers a reliable and qualitatively accurate framework for studying 2D colloidal fluids.
• The theory elucidates the formation of various mesophases driven by competing interactions.
• Confinement significantly alters the phase behavior of these 2D systems, leading to complex structures.