Release studies from lyotropic liquid crystal systems

Area of Science:

• Physical Chemistry
• Materials Science
• Surfactant Science

Background:

• Nonionic surfactants like polyoxethylene (20) isohexadecyl ether form complex phase behaviors with water.
• Understanding these phase behaviors is crucial for controlled release applications.

Purpose of the Study:

• To establish the temperature-composition diagram for polyoxethylene (20) isohexadecyl ether-water systems.
• To investigate the release kinetics of salicylic acid from liquid crystalline phases.
• To determine the influence of medium structure on interfacial resistance.

Main Methods:

• Phase diagram construction through temperature and composition variation.
• Salicylic acid release studies from various surfactant mesophases.
• Kinetic analysis of transfer rates and activation energy determination.

Main Results:

• Three distinct anisotropic regions were identified within the 33-80% concentration range of the surfactant.
• Salicylic acid release rates varied based on surfactant loading and molecular packing.
• Apparent activation energies differed significantly between ordered (33.3 kcal/mol) and isotropic (9.4 kcal/mol) media.

Conclusions:

• The structure of the surfactant-water medium profoundly affects the interfacial resistance of lipoidal barriers.
• Ordered mesophases present higher resistance to solute transfer compared to isotropic phases.
• These findings have implications for designing drug delivery systems utilizing surfactant-based liquid crystals.