Morphological Transformations in Solid Domains of Alkanes on Surfactant Solutions

Area of Science:

• Physical Chemistry
• Surface Science
• Colloid Science

Background:

• Alkanes can form distinct liquid (L), solid monolayer (S1), and hybrid bilayer (S2) phases at air-surfactant interfaces.
• Understanding phase behavior is crucial for applications involving interfaces.

Purpose of the Study:

• To investigate the phase coexistence and domain morphologies of alkanes on surfactant solutions.
• To elucidate the roles of line tension and electrostatic interactions in determining these morphologies.

Main Methods:

• Brewster angle microscopy was used to observe phase coexistence.
• Tetradecane, hexadecane, and their mixtures on tetradecyltrimethylammonium bromide solutions were studied.

Main Results:

• Phase coexistence of L, S1, and S2 phases was observed.
• Domain morphologies varied: S1 in L were long/thin, L in S1 broke into circular domains, and S2 domains were always circular.
• Morphology was dictated by the balance between line tension and electrostatic interactions.

Conclusions:

• The interplay between line tension and electrostatic forces governs alkane phase morphology at air-surfactant interfaces.
• Distinct phase behaviors and domain shapes arise from different phase pair interactions.