Rheophysical properties of fluorinated nonionic micellar phases

Area of Science:

• Materials Science
• Colloid and Surface Chemistry

Background:

• Micellar phases serve as templates for mesoporous silica synthesis.
• Fluorinated and hydrogenated surfactants form diverse micellar structures.
• Challenges exist in preparing ordered mesoporous materials from these structures.

Purpose of the Study:

• To characterize the rheophysical properties of a specific fluorinated surfactant's micellar phase (L(1)).
• To understand how temperature and concentration affect these properties.
• To investigate micellar behavior under flow conditions.

Main Methods:

• Preparation and characterization of the L(1) micellar phase using a fluorinated surfactant (R(F)(7)(EO)(8)).
• Rheological measurements under steady and dynamic flow conditions.
• Analysis of flow birefringence and extinction angle (χ) under shear.

Main Results:

• The L(1) phase exhibits Newtonian and shear-thinning fluid behavior based on temperature and concentration.
• A crossover between G' and G" at 20 wt % and 10 °C indicates long entangled micelles.
• The 20 wt % solution shows flow birefringence, with unexpected micellar orientation changes under increasing shear rate.

Conclusions:

• Proper characterization of micellar solutions is vital before silica precursor addition for successful mesoporous material synthesis.
• The rheological properties of R(F)(7)(EO)(8) solutions provide insights into micellar structuring and behavior.
• Unexpected flow-induced micellar orientation warrants further investigation.