Spontaneous Emulsification Produced by Chemical Reactions

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Materials Science

Background:

• Surfactants play a crucial role in stabilizing emulsions by influencing interfacial curvature.
• The properties of surfactants, such as their lipophilicity and hydrophilicity, determine the type of emulsion formed (e.g., water-in-oil or oil-in-water).
• Chemical modifications of surfactants can alter their properties and consequently affect emulsion behavior.

Purpose of the Study:

• To investigate the phenomenon of spontaneous emulsification induced by chemical transformation of surfactants.
• To explore how a change in surfactant spontaneous curvature affects oil solubilization and droplet nucleation.
• To demonstrate this effect in multiple chemical systems.

Main Methods:

• Three distinct chemical reaction systems were employed to convert lipophilic surfactants to hydrophilic ones in situ.
• System 1: Reaction of phenylboronic acid in water with a monoglyceride in oil.
• System 2: Diffusion of aqueous ethylenediaminetetraacetic acid (EDTA) into an oil phase containing a calcium sulfonate.
• System 3: Enzymatic hydrolysis of a double-chain phospholipid in an oil phase.

Main Results:

• Spontaneous emulsification of small oil droplets was observed in all three systems.
• The conversion of surfactants led to a reversal of spontaneous curvature from water-in-oil to oil-in-water.
• This curvature reversal decreased oil solubilization capacity, causing supersaturation and subsequent oil droplet nucleation.

Conclusions:

• Chemical reactions that alter surfactant hydrophilicity can induce spontaneous emulsification.
• The observed phenomenon is driven by a shift in spontaneous curvature and subsequent supersaturation.
• This study provides a novel method for generating oil-in-water emulsions via in-situ surfactant modification.