Interactions between adsorbed layers of cationic gemini surfactants

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Materials Science

Background:

• Cationic gemini surfactants are molecules with two hydrophilic head groups and two hydrophobic tails, linked by a spacer.
• Understanding surfactant behavior at interfaces is crucial for various applications, including detergency, emulsification, and drug delivery.

Purpose of the Study:

• To investigate the forces between glass and mica surfaces in the presence of two specific cationic gemini surfactants: 1,4 diDDAB and 1,12 diDDAB.
• To analyze the influence of surfactant concentration and spacer length on these surface forces below the critical micelle concentration (cmc).

Main Methods:

• Utilized two distinct surface force techniques to measure forces between surfaces.
• Investigated surfactant concentrations below the critical micelle concentration (cmc).

Main Results:

• Observed surface recharging at approximately 0.1 x cmc for both 1,4 diDDAB and 1,12 diDDAB.
• Repulsive double-layer forces were dominant at larger separations.
• Attractive forces or constant force regions were noted at smaller separations, attributed to desorption and rearrangement of the adsorbed surfactant layer.
• Analysis indicated that gemini surfactants were mostly dissociated, but ion pair formation increased with concentration and was higher for shorter spacer lengths.

Conclusions:

• Cationic gemini surfactants significantly alter surface forces, leading to phenomena like surface recharging and complex force profiles.
• The behavior of adsorbed surfactant layers is dynamic and influenced by surface proximity.
• Ion pair formation is a relevant factor in gemini surfactant behavior, particularly concerning spacer length and concentration.