Closed-cell crystalline foams: self-assembling, resonant metamaterials.

Area of Science:

• Materials Science
• Acoustic and Elastic Metamaterials
• Crystalline Foams

Background:

• Designing 3D acoustic/elastic metamaterials requires internal degrees of freedom and periodic structures for properties like negative effective mass.
• Closed-cell crystalline foams offer a promising base due to their inherent complex microstructure and internal resonances.
• Self-assembly techniques have enabled the creation of specific foam structures like Kelvin, face-centered cubic, and Weaire-Phelan.

Purpose of the Study:

• To investigate the potential of self-assembled crystalline foams as a basis for 3D metamaterials.
• To demonstrate the superanisotropic and unique mechanical properties arising from fluid-structure interactions in these foams.

Main Methods:

• Utilized self-assembly techniques to produce Kelvin (BCC), face-centered cubic, and Weaire-Phelan crystalline foams.
• Employed numerical modeling to analyze microstructural deformations and material behavior.
• Derived equivalent mechanical models from numerical simulation results.

Main Results:

• Demonstrated that the self-assembled foams exhibit superanisotropy, acting selectively as fluids or solids.
• Identified pentamode solid behavior resulting from fluid-structure interaction.
• Observed distinct regimes characterized by film resonances and a high density of states.

Conclusions:

• Self-assembled crystalline foams are a viable platform for realizing complex 3D metamaterials.
• These foams display extraordinary properties, including tunable fluid-solid behavior and resonance phenomena.
• The derived mechanical models provide a pathway for designing advanced acoustic and elastic metamaterials.