Time-resolved fluorescence and small angle neutron scattering study in pluronics-surfactant supramolecular assemblies

Area of Science:

• Supramolecular Chemistry
• Colloid and Surface Science
• Physical Chemistry

Background:

• Pluronic block copolymers form micelles with distinct hydrophobic cores and hydrophilic coronas.
• Cationic surfactants like CTAB can interact with and modify micellar structures.
• Understanding solute localization in mixed micelles is crucial for drug delivery and formulation science.

Purpose of the Study:

• To investigate the interaction between CTAB and Pluronic F88 and P105 micelles.
• To determine how CTAB modulates the location of an anionic solute within these mixed micelles.
• To elucidate the structural changes in pluronic micelles upon CTAB addition.

Main Methods:

• Time-resolved fluorescence spectroscopy to track probe dynamics.
• Small-angle neutron scattering (SANS) to analyze supramolecular assembly structure.
• Dynamic Stokes' shift measurements to confirm probe location changes.

Main Results:

• SANS confirmed the formation of pluronic-CTAB supramolecular assemblies with CTAB hydrophobic chains in the core and head groups at the core-corona interface.
• Anionic probe's rotational correlation time increased with CTAB concentration, indicating movement towards the micellar interior.
• The concentration of CTAB needed to internalize the probe correlated linearly with the pluronic corona thickness.

Conclusions:

• CTAB addition effectively modifies pluronic micelle structure and influences solute partitioning.
• Electrostatic interactions between CTAB and the anionic probe drive the probe's relocation into the micellar interior.
• The pluronic corona thickness is a key factor determining the amount of CTAB required for significant solute modulation.