Interface height fluctuations and surface tension of driven liquids with time-dependent dynamics

Area of Science:

• Soft Matter Physics
• Non-equilibrium Thermodynamics
• Computational Materials Science

Background:

• Energy input at the single-particle level can alter macroscopic properties of non-equilibrium systems.
• Interfaces in driven liquids offer a model for studying these energy-driven changes.
• Capillary wave theory (CWT) predicts interfacial fluctuation scaling in equilibrium systems.

Purpose of the Study:

• To investigate interfacial fluctuations in simulated driven liquids subjected to time-dependent forces.
• To determine the applicability of Capillary Wave Theory (CWT) to these non-equilibrium interfaces.
• To quantify the effect of driving forces on interfacial properties, such as surface tension.

Main Methods:

• Simulations of two phase-separated driven liquids: one with repulsive, one with attractive interactions.
• Analysis of interfacial fluctuation spectra under varying amplitudes of time-dependent driving forces.
• Comparison of simulation results with predictions from Capillary Wave Theory (CWT).

Main Results:

• In the repulsive system, CWT applicability varied with driving force amplitude.
• In the attractive system, interfacial fluctuations consistently obeyed CWT across all driving amplitudes.
• Effective surface tension in the attractive system increased linearly with driving force, exceeding equilibrium values.

Conclusions:

• Time-dependent driving forces significantly modify interfacial behavior in non-equilibrium liquids.
• CWT can be a valid framework for analyzing driven interfaces, particularly in attractive systems.
• The study demonstrates a method for extracting effective surface tension in driven systems and highlights the impact of energy input on material properties.