Phase Behavior of Lecithin at the Oil/Water Interface

Abstract

In order to elucidate the mechanism for the formation of an interfacial film providing enhanced emulsion stability by lecithin, we performed dynamic contacting experiments in which water was brought into contact with a solution of the phospholipid in n-decane. Two main phenomena were observed in the vicinity of the interfacial boundary on the side of the nonaqueous phase. The first to be noted was the formation of a thick interfacial film, visible even to the naked eye. The second was the separation of a liquid phase. On the basis of the combined data from our current and previous experiments, we suggest the mechanism for interfacial processes of which the basis is the lecithin organogel formation. Water transferring from aqueous solution into the nonpolar phase through a hydration of the adsorbed phospholipid promotes a sequence of phase or pseudophase transitions near the phase boundary between immiscible liquids: spherical reverse micelles f three-dimensional network from entangled wormlike micelles f organogel separation into a diluted solution and a compact gel or solid mass precipitating on the interfacial boundary.

Lecithin organogels as a potential phospholipid-structured system for topical drug delivery: A review

“…20,21 Further, the phase behavior of the ternary system is also shown to be dependent on lecithin concentrations employed for the formation of organogel system, and the phase separation has been noted to be abolished when the concentration of lecithin exceeds 200 mg/mL. 26,53,54 In one study, 26 using n-decane as the external media and lecithin at concentration smaller than 200 mg/mL, the gel formation was observed at n w = 1, while water was used as a polar additive. With subsequent addition of water (ie, at n w = n cr ), the organogel with maximum viscosity was obtained, but the phase separation of organogel occurred at n w 9 n cr (ie, at n w = 3.2-3.4), and a separated semisolid phase was found.…”

“…26,53,54 The same is defined in terms of the parameter, n w (ie, molar ratio of polar solvent to lecithin; n w = [polar solvent]/[lecithin]). 20,21 It is noted that the organogel as a homogenous phase exists over a very narrow range of polar solvent concentration.…”

“…Further increase in the amount of polar additive results in the formation of flexible, long tubular micelles of 2.0 to 2.5 nm radius and hundreds to thousands of nanometers in length. 53,54 After reaching a critical length, these extended micelles begin to overlap, entangle themselves, and build up a transient 3-dimensional network. 24,26,[58][59][60][61][62] This marks a crossover to a system characterized by increased viscosity and viscoelastic properties.…”

Multi-Response Optimization in the Formulation of a Topical Cream from Natural Ingredients

“…Therefore, sesame oil, Aloe vera gel, and the combination of soy lecithin/tween considerably decrease the creaming index, that is, the degree of destabilization of the emulsion. This can be due to the fact that soy lecithin has two tails, which are C16-C18 in length, and one of the tails has two cis unsaturations [24], which stabilizes better the emulsion oil in water [25]. In fact, soy lecithin has a low tendency to desorb, which fortifies the interfacial film, and the large headgroup of Tween provides steric repulsions between the oil droplets and prevents their coalescence [26].…”

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

“…These bonds are also responsible for the one dimensional growth of reverse micelles of lecithin. 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).…”