Multicomponent Diffusion in Aqueous Solutions of Nonionic Micelles and Decane.

Area of Science:

• Physical Chemistry
• Colloid Science
• Soft Matter Physics

Background:

• Understanding diffusion in crowded solutions is crucial for various applications, including drug delivery and material science.
• Surfactant-oil systems form micelles that exhibit complex behavior in solution, influenced by concentration and interactions.

Purpose of the Study:

• To measure the ternary diffusivity matrix and micelle gradient diffusion coefficient in aqueous solutions of decaethylene glycol monododecyl ether (C12E10) and decane.
• To investigate diffusion coupling between surfactant and decane.
• To characterize decane-containing micelles and compare experimental results with theoretical models.

Main Methods:

• Taylor dispersion technique to measure the ternary diffusivity matrix [D].
• Dynamic light scattering (DLS) to determine the micelle gradient diffusion coefficient.
• Static light scattering (SLS) to measure micelle aggregation number, hydration index, and hydrodynamic radius.

Main Results:

• C12E10 diffused down its gradient via micelle gradient diffusion, while decane diffused slower down its own gradient.
• Strong diffusion coupling observed: decane diffused down a surfactant gradient, and surfactant diffused up a decane gradient.
• Decane-containing micelles behaved as hard spheres with properties increasing linearly with solute-to-surfactant ratio.

Conclusions:

• A theoretical model based on Batchelor's theory accurately predicted the diffusivity matrix without adjustable parameters.
• Decane self-diffusion and surfactant gradient diffusion explain the observed concentration gradient movements.
• Intermicellar interactions and changes in micelle size/hydration drive the coupled diffusion phenomena.