Aqueous foam films stabilized by sodium naphthenates

Area of Science:

• Colloid and Surface Science
• Materials Science
• Physical Chemistry

Background:

• Foam films exhibit stratification (stepwise thinning) with moderate-to-high surfactant concentrations or solid particles.
• At moderate concentrations, stratification is attributed to ordered spherical micelles (Wasan and Nikolov model).
• High concentrations present phenomena suggesting a different structural organization within the film.

Purpose of the Study:

• To investigate the structural basis of foam liquid film stratification at high sodium naphthenate concentrations.
• To differentiate the stratification mechanism at high concentrations from that at moderate concentrations.
• To explore the presence of liquid crystalline structures in foam films.

Main Methods:

• Observation of foam films formed from aqueous sodium naphthenate solutions.
• Analysis of film thinning behavior and visual characteristics (e.g., domains of uniform color).
• Correlation of observed phenomena with known models of film stratification.

Main Results:

• Stratification in high-concentration sodium naphthenate films is linked to a lamellar liquid crystal-like (LLC-like) structure.
• This LLC-like structure may involve numerous oriented layers (potentially >100).
• The LLC-like structure can form within the film at bulk concentrations below the LLC phase's lower limit.

Conclusions:

• High concentrations of sodium naphthenate induce a lamellar liquid crystal-like structure in foam films, driving stratification.
• This mechanism differs from micelle-based stratification observed at moderate concentrations.
• The findings reveal the potential for ordered liquid crystalline structures in confined film geometries.