Effect of Adding Lecithin and Nonionic Surfactant on α-Gels Based on a Cationic Surfactant-Fatty Alcohol Mixture.

α-Gels are often used as base materials for cosmetics and hair conditioners. α-Gel-based commercial products typically contain many types of additives, such as polymers, electrolytes, oily components, and other surfactants, in addition to the three basic components. However, few systematic studies have been conducted on the effect of such additives on α-gels. In this study, we chose surfactant as an example to initiate the effect of such additives on the structure and rheological properties of α-gel samples formulated using cetyl alcohol (C16OH) and cetyltrimethylammonium chloride (CTAC). Optical microscopy analysis demonstrated that the size of the vesicles in the α-gel samples in this study was decreased via the addition of hydrogenated soybean lecithin (HSL) and penta(oxyethylene) cetyl ether (C16EO5), a nonionic surfactant, to them. Rheological measurements revealed that at high C16OH/CTAC ratios, the viscosity and yield stress of the α-gel samples decreased owing to the addition of surfactants to them. Conversely, at low C16OH/CTAC ratios, the opposite tendency was observed. Small-angle X-ray scattering analysis indicated that for the α-gel samples with high C16OH/CTAC ratios, the addition of HSL or C16EO5 to them decreased the interlayer spacing of their lamellar bilayer stack, which led to the changes in the rheological properties of the α-gel samples.

Formulation of Bicelles Based on Lecithin-Nonionic Surfactant Mixtures.

Bicelles have been intensively studied for use as drug delivery carriers and in biological studies, but their preparation with low-cost materials and via a simple process would allow their use for other purposes as well. Herein, bicelles were prepared through a semi-spontaneous method using a mixture of hydrogenated soybean lecithin (SL) and a nonionic surfactant, polyoxyethylene cholesteryl ether (ChEO10), and then we investigated the effect of composition and temperature on the structure of bicelles, which is important to design tailored systems. As the fraction of ChEO10 (XC) was increased, a bimodal particle size distribution with a small particle size of several tens of nanometers and a large particle size of several hundred nanometers was obtained, and only small particles were observed when XC ≥ 0.6, suggesting the formation of significant structure transition (liposomes to bicelles). The small-angle neutron scattering (SANS) spectrum for these particles fitted a core-shell bicelle model, providing further evidence of bicelle formation. A transition from a monomodal to a bimodal size distribution occurred as the temperature was increased, with this transition taking place at lower temperatures when higher SL-ChEO10 concentrations were used. SANS showed that this temperature-dependent size change was reversible, suggesting the SL-ChEO10 bicelles were stable against temperature, hence making them suitable for several applications.

Cholesterol-Induced Formation of Liquid Ordered Phase-Like Structures in Non-Phospholipid Systems.

The formation of liquid ordered (Lo) phase-like structures in stearyltrimethylammonium chloride/cholesterol/1,3-butanediol/water and hepta(oxyethylen) octadecyl ether/cholesterol/1,3-butanediol/water systems was investigated. Differential scanning calorimetry and X-ray scattering measurements confirmed that Lo phase-like structures were formed in both surfactant/cholesterol systems, similar to the lysophospholipid/cholesterol system. It was revealed that the concentration of cholesterol at which only Lo phase-like structures are formed increases in the order stearyltrimethylammonium chloride < lysophospholipid < hepta(oxyethylen) octadecyl ether. In addition, for both surfactants, the interlayer spacing, d, was larger for Lo phase-like structures than for α-gel structures. These results suggest that the ionicity and structure of the hydrophilic group of each surfactant play important roles.

Study on the formation of liquid ordered phase in lysophospholipid/cholesterol/1,3-butanediol/ water and lysophospholipid/ceramide/1,3- butanediol/water systems.

Formation of a liquid ordered phase in lysophospholipid/cholesterol/1,3-butanediol/water and lysophospholipid/ceramide/1,3-butanediol/water systems was investigated. Differential scanning calorimetry confirmed that a liquid ordered phase was formed in the lysophospholipid/cholesterol/1,3-butanediol/water system similar to that in phospholipid systems. The structure of liquid ordered phase was analyzed by using X-ray scattering measurements. It was revealed that the liquid ordered phase has a lamellar structure in which the hydrophobic chains are less ordered than in α-type crystals. On the other hand, in the lysophospholipid/ceramide/1,3-butanediol/water system, a liquid ordered phase was not formed.

Phase behavior and hydrated solid structure in lysophospholipid/long-chain alcohol/water system and effect of cholesterol addition.

Phase behavior in lysophospholipid/long-chain alcohol/water system at 80°C was investigated using hexanol and oleyl alcohol as the long-chain alcohol. Similarly to hydrophilic surfactant, a micellar phase in a lysophospholipid/water system transitioned to a lamellar liquid-crystalline phase by the addition of long-chain alcohol. In the oleyl alcohol system the lamellar liquid-crystalline phase was observed in wider region compared to the hexanol system. The effect of cholesterol addition on the phase behavior was also studied. The region of liquid-crystalline phase and (reverse micellar + liquid-crystalline + water) phase shifted towards higher lysophospholipid concentrations. The structure of hydrated solid as well as the transition between lamellar liquid-crystalline phase and hydrated solid was analyzed by X-ray scattering measurement and differential scanning calorimetry measurement. It was revealed that the hydrated solid was α-type crystals with lamellar structure. The hydrated solid (gel)-liquid crystal transition temperature gradually decreased with increasing oleyl alcohol concentration and the decrement was enhanced by the addition of cholesterol.

Phase behavior and froth stability in a water/lysophospholipid system.

Phase behavior in a water/lysophospholipid system was investigated. A hydrated solid phase is observed at low temperature. Above the melting temperature of the hydrated solid a micellar phase at low surfactant concentration and a liquid crystalline phase at high surfactant concentration were observed. Similarly to poly(oxyethylene)-type nonionic surfactant systems, clouding behavior takes place at high temperature. The concentration of micelle-liquid crystal transition shifts to higher surfactant concentration in acidic or basic condition, but polyhydric alcohol addition does not affect very much on this transition point. The effect of added inorganic salts on the phase behavior was also studied, and the change in melting temperature of the hydrated solid and the cloud point shows a trend of the order of Hofmeister series. At room temperature a solid phase and an aqueous phase are equilibrated and one can obtain rather stable froth by shaking the sample that may be stabilized by the adsorption of solid dispersions on the air-water interface. The effect of inorganic salts on the froth stability in the water/lysophospholipid system was studied. The inorganic salts with salting-out effect improved froth stability.