Sphere to rod transitions in self assembled systems probed using direct force measurement

Area of Science:

• Colloid and Surface Science
• Materials Science
• Physical Chemistry

Background:

• Understanding nanoparticle shape influence on surface forces is crucial for colloidal fluid properties.
• Micelle shape transitions, from spheres to rods, are not well-investigated phenomena.
• Surfactant solutions with varying micelle morphologies are key to studying these effects.

Purpose of the Study:

• To investigate the effect of nanoparticle (micelle) shape on surface forces in concentrated surfactant solutions.
• To analyze how the transition from spherical to rod-like micelles alters colloidal fluid behavior.
• To provide insights into emulsion flocculation and handling in systems with anisotropic micelles.

Main Methods:

• Utilized atomic force microscopy (AFM) with rigid particle and soft droplet probes.
• Measured surface force behavior in concentrated solutions of cetyltrimethylammonium bromide and sodium salicylate.
• Employed the Chan-Dagastine-White model for data analysis and comparison.

Main Results:

• Minor changes in micelle shape showed no significant impact on surface force behavior.
• Significant elongation of micelles led to a change in long-range forces from oscillatory to a single attractive well.
• Demonstrated a clear correlation between micelle aspect ratio and the nature of surface forces.

Conclusions:

• Nanocolloid shape is a critical factor governing the properties and behavior of colloidal fluids.
• The transition to rod-like micelles fundamentally alters surface force interactions.
• Findings are significant for understanding and controlling emulsion flocculation and handling in complex micellar systems.