Surface-induced assembly of sophorolipids

Area of Science:

• Surface Chemistry
• Materials Science
• Biophysics

Background:

• Sophorolipids are microbial glycolipids with pH-responsive behavior in solution.
• They typically form micelles but can assemble into platelets and fibers.
• Understanding their surface self-assembly is crucial for applications.

Purpose of the Study:

• To investigate the surface self-assembly of acidic sophorolipids.
• To determine the influence of substrate surface energy and solution pH.
• To correlate self-assembly structures with surface properties.

Main Methods:

• Dip-coating on gold, silicon(111), and TiO2 anatase substrates.
• Optimization of deposition parameters: withdrawal speed, humidity, and temperature.
• Characterization using atomic force microscopy (AFM) and scanning electron microscopy (SEM).
• Analysis of surface energy components using the Good-van Oss approach.

Main Results:

• Optimal self-assembly achieved at 1 mm/s withdrawal speed, 25°C, and 25% relative humidity.
• When surface energy is dominated by dispersive forces, sophorolipids form entangled needles irrespective of pH.
• When surface energy is dominated by electronic forces, pH significantly influences assembly into homogeneous layers, isolated aggregates, or 2D fibrillar networks.

Conclusions:

• Substrate surface energy and solution pH are key factors controlling sophorolipid surface self-assembly.
• Tailoring surface properties allows for predictable organization of sophorolipids.
• This provides a basis for designing functional materials with controlled glycolipid structures.