The bouncing threshold in silica nanograin collisions.

Area of Science:

• Materials Science
• Nanotechnology
• Computational Physics

Background:

• Understanding nanoparticle collisions is crucial for fields like powder technology and additive manufacturing.
• Existing models often simplify nanoparticle interactions, neglecting surface effects and complex deformation behaviors.

Purpose of the Study:

• To investigate the mechanics of amorphous silica nanoparticle collisions using molecular dynamics simulations.
• To evaluate the applicability of the Johnson-Kendall-Roberts (JKR) model in describing these collisions.
• To characterize the transition between sticking and bouncing behaviors as a function of impact velocity and particle size.

Main Methods:

• Employing molecular dynamics (MD) simulations to model collisions between amorphous silica nanoparticles.
• Utilizing a silica model with uncontaminated surfaces, excluding effects of hydroxylation or adsorbed water.
• Analyzing central collisions to determine the sticking-bouncing boundary and quantify the coefficient of restitution.

Main Results:

• The Johnson-Kendall-Roberts (JKR) model accurately describes the initial phase of collision up to maximum compression.
• The JKR model underestimates the closest approach distance due to emergent plasticity (localized shear transformation zones).
• The JKR model significantly underestimates contact radius and collision duration during separation, failing to capture covalent bond breaking dynamics.

Conclusions:

• Plasticity and bond rupture during silica nanoparticle separation are key phenomena not captured by the JKR model.
• The JKR model's limitations highlight the need for more sophisticated models to accurately predict nanoparticle collision outcomes, especially during separation.
• The study provides insights into the adhesive neck collapse and filament formation/tearing during nanoparticle impacts.