Lecithin Organogel with New Rheological and Scaling Behavior

Abstract

It was established from an experimental study on a lecithin organogel in n-decane performed by means of an oscillatory rheology that frequency dependencies for complex viscosity and storage modulus have intermediate plateaus at certain molar ratios of water to lecithin. This type of rheological behavior was previously observed for blends of homopolymers which differ significantly in their molecular weight. To mathematically describe the experimental data, a Maxwell model including two relaxation processes (i.e., two elements in parallel) was considered. Both relaxation modes were constrained according to the known interrelation between terminal relaxation time, zero-shear viscosity, and plateau modulus. The experimental results were in good agreement with the model considered. By applying a fitting procedure, two sets of values for relaxation time, zero-shear viscosity and plateau modulus, were obtained for each of the relaxation processes. When the scaling behavior was examined, a disagreement with current models for the polymer-like micelles was found. The presented results lead to a suggestion that the lecithin organogel at increased water-to-lecithin molar ratios has more complicated structural organization than that observed for surfactant based micellar aggregates before.

Aggregated Assemblies of Sodium Dodecyl Sulfate/Dimethyldodecyl Ammoniopropane Sulfonate and Phospholipids at the Interface and in the Bulk

“…Thus, the bilayer structures lead to the formation of vesicles or liposomes, the size of which is significantly dependent upon the number of factors such as concentration (1,2), temperature (3), ionic strength (3,4), morphological changes, etc. Since the phospholipids with higher fatty acid chains only exist in the form of bilayer structures, they can be studied as the model system for biomembranes (5)(6)(7)(8)(9).…”

Organogels in Drug Delivery: A Special Emphasis on Pluronic Lecithin Organogels

“…Long tubular micelles of 2.0-2.5 nm radius and hundreds to thousands of nanometers will be formed upon further addition of polar solvent (39,40). Once these micelles attain a critical length, they start to overlap, followed by the intertwining, which results in the formation of a three-dimensional network (29,(41)(42)(43)(44)(45)(46). This offers the system an enhanced viscosity and viscoelastic property, which results in the formation of a jellylike structure.…”

Lecithin Organogels in Enhancing Skin Delivery of Drugs

“…Compatibility studies with human skin revealed that topical use of LOs is safe (Dreher et al 1997 ;Shchipunov et al 2001 ;Schurtenberger et al 1990 ). Vehicles (organic solvents, such as fatty acid esters, e.g., isopropyl myristate, ethyl oleate) used for preparing LOs are also GRAS excipients.…”

“…If polar additive concentration is increased further, fl exible and long tubular micelles from 2.0 to 2.5 nm in radius and nanometer length are formed (Shchipunov and Schmiedel 1996a, b). After reaching a critical length, these extended micelles begin to overlap, entangle themselves, and build up a transient 3-dimensional network (Shchipunov and Hoffmann 2000 ;Voit and Shchipunov 2000 ;Shchipunov et al 2001 ).…”