Dirhamnolipid ester - formation of reverse wormlike micelles in a binary (primerless) system.

Area of Science:

• Supramolecular Chemistry
• Colloid and Surface Science
• Materials Science

Background:

• Dirhamnolipid esters are amphiphilic molecules with potential self-assembly properties.
• Reverse wormlike micelles typically require co-surfactants or primers in nonpolar solvents.
• Understanding self-assembly in binary systems is crucial for developing novel materials.

Purpose of the Study:

• To investigate the self-assembly of dirhamnolipid esters in nonpolar solvents.
• To determine the influence of concentration and alkyl chain length on rheological properties.
• To characterize the formation and structure of reverse wormlike micelles.

Main Methods:

• Rheological measurements (oscillatory shear) to assess viscoelasticity.
• Polarized light microscopy to observe network formation.
• Differential scanning calorimetry (DSC) to determine transition enthalpy.
• Investigation of varying dirhamnolipid ester concentrations and alkyl chain lengths in toluene.

Main Results:

• Formation of highly viscoelastic solutions (gels) at low dirhamnolipid ester concentrations (<1 wt%).
• Reverse wormlike micelle formation favored by shorter alkyl chain lengths.
• Maxwell model fitting and Cole-Cole plot analysis confirmed wormlike micelle behavior.
• Birefringence and anisotropic behavior observed, indicating network structures.
• DSC revealed a transition enthalpy of ±7.2 kJ/mol, indicative of strong dispersion forces.

Conclusions:

• Dirhamnolipid esters can form reverse wormlike micelles and gels in nonpolar solvents without primers, a rare binary system behavior.
• Rheological and structural properties are tunable via concentration and alkyl chain length.
• The observed gelation is attributed to the entanglement of wormlike micelles driven by alkyl chain interactions.