Equilibrium topology and partial inversion of Janus drops: a numerical analysis

Area of Science:

• Colloid and Surface Science
• Materials Science
• Physical Chemistry

Background:

• Janus emulsions, composed of two immiscible oils (O1, O2) and water (W), exhibit complex interfacial behavior.
• Understanding the equilibrium topology of these emulsions is crucial for their application in advanced materials and formulations.
• Interfacial tensions and volume fractions are key parameters dictating emulsion structure.

Purpose of the Study:

• To numerically evaluate the equilibrium topology of an aqueous Janus emulsion [(O1+O2)/W].
• To determine the relative significance of local equilibrium and volume fraction on Janus drop topology.
• To investigate the effect of varying interfacial tensions, specifically γO1/W, on emulsion structure.

Main Methods:

• Numerical evaluation of equilibrium topology for a three-liquid system (O1, O2, W).
• Simulation using realistic interfacial tension values: γO2/W = 5 mN m⁻¹, γO1/O2 = 1 mN m⁻¹, and varying γO1/W (4-5 mN m⁻¹).
• Analysis of the impact of local equilibrium at the three-phase contact line and dispersed liquid volume fractions.

Main Results:

• Local equilibrium at the contact line dominantly affects the O1 coverage fraction on the O2 drop surface.
• Interfacial tension balance has a modest impact on O1 coverage for a constant O2 volume and infinite O1 volume.
• Emulsion inversion was observed when O1 volume exceeded a critical value, transitioning to a (W+O2)/O1 Janus configuration.

Conclusions:

• Local equilibrium is the primary driver for O1 surface coverage in (O1+O2)/W Janus emulsions.
• A critical O1 volume fraction can induce emulsion inversion, fundamentally altering the continuous and dispersed phases.
• The findings provide insights into the stability and structural transitions of multi-oil Janus emulsions.