Polymer loaded microemulsions: Changeover from finite size effects to interfacial interactions

Area of Science:

• Physical Chemistry
• Materials Science
• Soft Matter Physics

Background:

• Microemulsions exhibit form fluctuations crucial for their properties.
• Water-in-oil microemulsions with dioctyl sodium sulfosuccinate are model systems.
• Polyethylene glycol (PEG) addition modifies microemulsion droplet behavior.

Purpose of the Study:

• Investigate the impact of polymer addition on microemulsion droplet fluctuations.
• Determine how droplet size influences polymer effects on surfactant shell properties.
• Elucidate the interplay between structural and dynamical properties in modified microemulsions.

Main Methods:

• Dielectric spectroscopy (DS) for probing droplet dynamics.
• Neutron spin echo spectroscopy (NSE) for analyzing fluctuations.
• Analysis of microemulsions with varying droplet sizes and polymer concentrations.

Main Results:

• Polymer addition alters droplet fluctuations, affecting the bending modulus of the surfactant shell.
• Small droplets (<37 Å) show a reduced bending modulus with polymer addition.
• Large droplets exhibit complex changes in bending modulus, confirmed by both DS and NSE.
• Structural changes are size-independent, while dynamical properties vary with polymer content.
• Finite size effects dominate for small droplets, transitioning to polymer-surfactant interactions in larger ones.

Conclusions:

• Polymer-induced changes in microemulsion bending modulus are size-dependent.
• Dynamical properties and polymer-surfactant interactions play a key role in large droplets.
• The study reveals a shift in the dominant factors influencing bending modulus with increasing droplet size.