Structure of microemulsions in the continuous phase channel

Area of Science:

• Physical Chemistry
• Materials Science
• Colloid and Surface Chemistry

Background:

• Nonionic C12E5 and ionic AOT surfactants are widely used in various applications.
• Understanding their phase behavior is crucial for optimizing their performance.
• Existing models may not fully capture the complex structures of these systems.

Purpose of the Study:

• To investigate and elucidate the microemulsion and lamellar phase structures of C12E5 and AOT surfactant systems.
• To compare the suitability of different structural models, including the symmetric disordered open connected lamellar (DOC-lamellar) and standard flexible models.
• To analyze the influence of temperature and salt on the observed structures.

Main Methods:

• Utilized conductivity measurements to probe surfactant structures and interactions.
• Applied and compared various structural models (DOC-lamellar, standard flexible model) to experimental data.
• Investigated phase behavior across different temperature ranges.

Main Results:

• C12E5 systems are best described by the DOC-lamellar model, differing from the standard flexible model.
• AOT systems exhibit bicontinuous microemulsion structures (standard flexible model) at high temperatures.
• At room temperature, AOT forms connected cylinders in a molten cubic crystal phase.
• Significant surface area loss due to fluctuations and defects was observed in the lamellar phase for both systems.
• Salt adsorption in ethoxy groups is dominant for C12E5, while tortuosity versus cation absorption is key for AOT.

Conclusions:

• The study provides refined structural models for C12E5 and AOT surfactant systems.
• Findings highlight the limitations of commonly employed models and introduce more accurate descriptions.
• Conductivity measurements offer critical insights into salt adsorption and structural characteristics.