Dynamics of phase-separated interfaces in inhomogeneous and driven mixtures

Area of Science:

• Physics of soft matter
• Thermodynamics
• Fluid dynamics

Background:

• Phase-separated binary mixtures exhibit complex interface dynamics.
• Spatio-temporal modulations can influence material properties like surface tension.
• Thermophoresis describes particle movement in response to temperature gradients.

Purpose of the Study:

• To derive effective equations for sharp interface dynamics in binary mixtures.
• To investigate the role of surface tension heterogeneities in driving interface motion.
• To quantify the dynamics of thermophoretic droplets under modulated conditions.

Main Methods:

• Derivation of effective equations of motion for sharp interfaces.
• Modeling of surface tension gradients as effective capillary forces.
• Application of the sharp interface model to thermophoretic droplets.

Main Results:

• Spatial heterogeneities in surface tension induce effective capillary forces, driving interface motion independently of hydrodynamics.
• Droplet deformation and transport are governed by a balance of bulk and capillary forces, dependent on droplet size.
• Small thermophobic droplets (positive Soret coefficient) can migrate towards higher temperatures due to capillary forces.

Conclusions:

• Capillary forces arising from surface tension gradients are a significant driver of interface motion in binary mixtures.
• Droplet behavior in thermophoresis is a complex interplay between bulk and capillary effects, tunable by droplet size.
• Unexpected migration of thermophobic droplets towards heat highlights the dominant role of capillary forces in specific regimes.