Double-Chain Cationic Surfactants: Swelling, Structure, Phase Transitions and Additive Effects

Area of Science:

• Physical Chemistry
• Materials Science
• Colloid and Surface Chemistry

Background:

• Double-chain amphiphilic compounds like surfactants and lipids are crucial in personal care and biological applications.
• Dioctadecyldimethylammonium chloride (DODAC) is a key compound used in products such as hair conditioners.
• Understanding DODAC's phase structures and transitions is vital for optimizing its applications.

Purpose of the Study:

• To investigate the phase structures and transitions of dioctadecyldimethylammonium chloride (DODAC) bilayers.
• To examine the impact of additives with varying polarities on DODAC's phase behavior.
• To characterize the resulting phase structures and transition temperatures.

Main Methods:

• Differential scanning calorimetry (DSC) for thermal analysis.
• Small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) for structural characterization.
• Analysis of alkyl chain distances, bilayer thicknesses, and phase identification.

Main Results:

• Two primary bilayer lamellar phases, Lβ (solid chains) and Lα (melted chains), dominate DODAC's phase behavior.
• Additives significantly influence phase stability and structure, with polarity being a key factor.
• Fatty acids and alcohols induce distinct structural changes, while urea has minimal effect; some additives promote transitions to cubic or hexagonal liquid crystalline phases.

Conclusions:

• The phase behavior of DODAC is sensitive to the polarity of incorporated additives.
• Specific additives can stabilize or destabilize lamellar phases and induce transitions to novel liquid crystalline structures.
• Dilution with water can trigger phase transitions in systems modified by certain additives.