Densest versus jammed packings of bent-core trimers

Area of Science:

• Physics
• Materials Science
• Chemistry

Background:

• Understanding particle packing is crucial for materials science and physics.
• Jamming transitions in granular materials are complex phenomena.
• Trimer particles introduce unique geometric constraints compared to monomers.

Purpose of the Study:

• To investigate the formation of dense crystalline packings of tangent-sphere trimers.
• To contrast these crystalline states with disordered jammed states under compression.
• To analyze the influence of fixed bond angles on packing density and jamming.

Main Methods:

• Computational modeling of tangent-sphere trimers with fixed bond angles.
• Simulations of quasistatic and dynamic athermal compression.
• Analysis of packing fractions (ϕ) for crystalline and jammed states.
• Characterization of structural order and disorder.

Main Results:

• Putatively maximally dense packings of trimers were identified.
• Dense 3D crystals form for all fixed bond angles (θ₀), with packing fractions (ϕ_{max}) exceeding 0.97ϕ_{cp}.
• Periodic structures with close-packed bilayers/trilayers and gap layers were observed.
• Jamming fractions (ϕ_{J}) are significantly lower than for monomers, indicating jamming is promoted by trimer constraints.
• ϕ_{J} strongly depends on θ₀, with straight trimers minimizing it and closed trimers maximizing it.
• Lower ϕ_{J} correlates with increased disorder in marginally jammed states.

Conclusions:

• Fixed bond angles in trimers do not prevent dense crystal formation, even when incommensurate with ideal packing.
• Trimer constraints inherently promote jamming compared to monomers.
• The degree of disorder in jammed states is quantifiable and linked to packing fraction and bond angle.
• Trimer linearity influences configurational freedom and jamming behavior.