Nanoemulsions prepared by a two-step low-energy process.

Area of Science:

• Colloid and Surface Science
• Materials Science
• Physical Chemistry

Background:

• Nanoemulsions are thermodynamically stable or kinetically stable systems with droplet sizes typically ranging from 20 to 200 nm.
• The formation and stability of nanoemulsions are influenced by factors such as surfactant type, oil phase, water content, and preparation method.

Purpose of the Study:

• To investigate the formation and structure of nanoemulsions using a simple, low-energy two-step dilution process.
• To determine the influence of initial concentrate phase behavior on nanoemulsion properties.
• To elucidate the underlying mechanism of nanoemulsion formation and stability.

Main Methods:

• Preparation of oil/surfactant/water systems using various surfactants including pentaoxyethylene lauryl ether (C12E5).
• Characterization of nanoemulsions using dynamic light scattering (DLS) and small-angle neutron scattering (SANS).
• Analysis of phase behavior of the initial concentrates.

Main Results:

• Transparent nanoemulsions with droplet radii around 15 nm were formed from a bicontinuous microemulsion concentrate.
• Opaque emulsions formed when the concentrate was in an emulsion-phase region.
• SANS data revealed spherical core-shell (decane-C12E5) nanodroplets that remained structurally stable upon dilution.
• Discrepancies between DLS and SANS droplet size measurements suggest long-range droplet interactions.

Conclusions:

• Nanoemulsion droplet structure is primarily dictated by the phase behavior of the initial concentrate, not the dilution process.
• Homogeneous nucleation of oil droplets during emulsification is proposed as a general mechanism for nanoemulsion formation.
• The findings offer a new perspective on nanoemulsion stability compared to previous studies.