Interactions between a nonionic gemini surfactant and cyclodextrins investigated by small-angle neutron scattering

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Colloid Science

Background:

• Gemini surfactants offer unique properties due to their dual structure.
• Cyclodextrins are known for their ability to form inclusion complexes.
• Understanding the self-assembly of surfactant-cyclodextrin systems is crucial for developing new materials.

Purpose of the Study:

• To investigate the microstructure of complexes formed between hydroxypropyl-cyclodextrins (HPCDs) and a novel nonionic hetero-gemini surfactant (NIHG750).
• To elucidate the influence of different HPCD types (alpha, beta, gamma) and concentrations on aggregate formation.

Main Methods:

• Small-angle neutron scattering (SANS) was employed to study the aggregate structures.
• Various form factor models were used to fit the SANS data and characterize the aggregates.

Main Results:

• Spherical aggregates (25-40 Å) were observed, larger than NIHG750 micelles (23 Å), suggesting partial cyclodextrin coverage.
• Rod formation (r ≈ 8 Å, L ≈ 70 Å) was detected, indicating HPCD threading onto NIHG750 and surfactant extension.
• The tendency for rod formation increased in the order gamma-CD < alpha-CD < beta-CD, with higher HPCD concentrations favoring rods.

Conclusions:

• HPCDs interact with NIHG750, leading to the formation of both spherical and rod-shaped aggregates.
• The observed structures are consistent with HPCDs threading onto the surfactant, altering its conformation and micellar assembly.
• HPCD type and concentration significantly control the resulting microstructure, with HPbetaCD showing the strongest tendency for rod formation.