Effective structure factor of osmotically deformed nanoemulsions

Area of Science:

• Colloid and Surface Science
• Soft Matter Physics
• Materials Science

Background:

• Nanoemulsions are versatile systems with applications in food, pharmaceuticals, and cosmetics.
• Understanding droplet packing and phase behavior is crucial for controlling nanoemulsion properties.
• Biliquid foams represent a unique state of matter with potential for novel material design.

Purpose of the Study:

• To investigate the structural evolution of nanoemulsion droplets under extreme osmotic compression.
• To explore the transition from spherical droplet packing to polyhedral foam structures.
• To determine the influence of droplet deformability and inter-droplet interactions on structural changes.

Main Methods:

• Preparation of uniform silicone oil-in-water nanoemulsions stabilized by sodium dodecyl sulfate.
• Application of ultracentrifugation to achieve extreme osmotic compression and high volume fractions.
• Utilizing small-angle neutron scattering (SANS) to probe the structure factor over a wide range of wavenumbers.

Main Results:

• Nanoemulsion droplets can be compressed to high volume fractions, forming solidlike biliquid foams without significant coalescence.
• At low volume fractions, droplet structure aligns with hard sphere predictions; however, anionic repulsion and deformability cause deviations at higher fractions.
• Beyond the maximal random jamming volume fraction (phiMRJ = 0.64), the structure factor exhibits a primary peak below unity, indicating significant droplet deformation.

Conclusions:

• Extreme osmotic compression effectively induces structural transitions in nanoemulsions.
• Droplet deformation into nonspherical shapes is a key feature near and beyond the jamming limit.
• The observed subunity primary peak in the structure factor suggests a transition towards a polyhedral foam morphology.