Structural relaxation and rheological response of a driven amorphous system

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Physics

Background:

• Amorphous systems exhibit sluggish dynamics and two-step relaxation near ideal glass transition temperatures.
• Mode coupling theory identifies an ideal glass transition temperature (Tc) in binary Lennard-Jones mixtures.
• Understanding structural relaxation under shear is crucial for predicting material behavior.

Purpose of the Study:

• Investigate the signature of ideal glass transition under shear-driven dynamics.
• Distinguish structural relaxation mechanisms in supercooled versus glassy states under shear.
• Analyze the rheological response and flow curves in relation to structural changes.

Main Methods:

• Molecular dynamics simulations of an 80:20 binary Lennard-Jones mixture.
• Analysis of correlation functions to probe structural relaxation.
• Rheological measurements including shear viscosity and flow curves.

Main Results:

• Structural relaxation in the supercooled state is shear-dominated at high rates but recovers equilibrium at low rates.
• In the glassy state, structural relaxation is always shear-driven.
• Shear viscosity exhibits shear thinning in the supercooled state and diverges at zero shear rate in the glassy state.
• A stress plateau is observed in flow curves for the glassy phase at low shear rates.

Conclusions:

• Shear motion fundamentally alters structural relaxation dynamics in amorphous systems near the glass transition.
• A transition to a non-ergodic state occurs in driven glasses as shear rate approaches zero.
• The observed stress plateau has implications for fluid flow in glassy materials.