Structure of saturated random-sequential-adsorption ellipse packings

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Materials Science

Background:

• Recent observations of liquid glass in ellipsoidal colloid suspensions.
• Understanding the structural properties of saturated random sequential adsorption (RSA) ellipse packings is crucial.

Purpose of the Study:

• To determine packing fractions (ϕs(α)) for ellipse packings with high precision.
• To explore the variation of positional-orientational order with aspect ratio (α).
• To identify structural transitions and their relation to local disorder.

Main Methods:

• Analysis of saturated RSA ellipse packings.
• High-precision determination of packing fractions.
• Investigation of positional-orientational pair correlation functions (gmax).

Main Results:

• An empirical analytic formula for ϕs(α) was developed, predicting values within 0.1% accuracy for α ≤ 10.
• A structural transition from tip/side- to side/side-contact dominance was observed at αTS ≈ 2.4.
• At αTS, the peak positional-orientational correlation (gmax) is minimal, indicating maximal local disorder.
• gmax increases exponentially with decreasing α for α < 2.4 and increasing α for α > 2.4.
• Nematic order and experimental precursor-like structures emerge for α > 3.
• Lamellar structures and density fluctuations increase with α for α ≳ 5, approaching the rodlike limit.

Conclusions:

• The study provides a precise formula for ellipse packing fractions and characterizes structural transitions.
• A key transition at α ≈ 2.4 signifies a shift towards maximal local disorder.
• The findings offer insights into the self-assembly and phase behavior of ellipsoidal particles.