Micellar structure in gemini nonionic surfactants from small-angle neutron scattering.

Area of Science:

• Colloid and Surface Science
• Polymer Chemistry
• Materials Science

Background:

• Nonionic gemini surfactants are dimeric molecules with potential applications in various fields.
• Understanding micelle formation is crucial for surfactant behavior and applications.
• Poly(oxyethylene) alkanols are widely studied monomeric surfactants.

Purpose of the Study:

• To determine the size and shape of micelles formed by polyoxyethylene (nonionic gemini) surfactants.
• To investigate the influence of alkyl and ethoxy chain lengths on micelle morphology.
• To explore the relationship between surfactant structure and solution properties.

Main Methods:

• Small angle neutron scattering (SANS) was employed to analyze micelle structure.
• Systematic variation of alkyl (n=12-20) and ethoxy (m=5-30) chain lengths.
• Characterization of micelle size, shape, and solution properties.

Main Results:

• Longer ethoxylated chains are necessary for gemini surfactant solubility.
• Micelle corona structure is well-modeled as a homogeneous random coil.
• Spherical micelles form with long ethoxy chains; shorter chains yield rods and vesicles.
• A sphere-to-rod transition was observed upon warming, accompanied by increased viscosity and gelation for specific surfactants.

Conclusions:

• The ethoxy chain length is a critical factor controlling micelle morphology in nonionic gemini surfactants.
• The observed transitions and gelation phenomena offer insights into potential applications.
• SANS is an effective technique for elucidating the structure of surfactant assemblies.