Aggregation Characteristics of Biobased Anionic Surfactant, Hydroxy Alkane Sulfonate in Aqueous CaCl Solutions: Vesicle and Supported Bilayer Formation.

Vesicles are known to spontaneously adsorb onto solid-liquid interfaces and to form supported bilayers in aqueous solution. Cationic surfactants have typically been used to generate supported bilayers because solid surfaces in water are often negatively charged. The present study investigated the aggregation behavior of an anionic surfactant, hydroxy alkane sulfonate having a C18 alkyl chain (C18HAS) in aqueous CaCl solutions.

Thermodynamically stable structure of hydroxy alkane sulfonate surfactant monomers in water achieving high water solubility and a low CMC.

Although sodium internal olefin sulfonates (IOSs) derived from petrochemicals are known to act as anionic surfactants, these compounds have few practical applications and their interfacial properties have not been examined in detail because they have complex compositions and are challenging to prepare. However, IOSs obtained from vegetable oils have recently been applied to detergents. The present work represents the first study of the IOS sodium 5-hydroxyhexadecane-4-sulfonate (C16-4S-5OH) as a pure substance.

Adsorption and Lubrication of α-Gel (α-Form Hydrated Crystal) Dispersion at Solid/Liquid Interfaces.

We characterized the adsorption and desorption of α-gel (α-form hydrated crystal) dispersions in aqueous media using a quartz crystal microbalance with dissipation monitoring (QCM-D) technique. The α-gel was formed from a mixture of N-[3-(dimethylamino)propyl]docosanamide (APA-22) L-lactic acid salt, 1-octadecanol (COH), and water. The solid substrate employed in this study as a model for hair was silica.

Effects of Domain Size on Viscosity of α-Gel (α-Form Hydrated Crystal) Prepared from Eco-friendly Cationic Surfactant.

We determine the effects of the α-gel (α-form hydrated crystal) domain size on the viscosity of water-diluted α-gels consisting of the N-[3-(dimethylamino)propyl]docosanamide (APA-22) L-lactic acid salt, 1-octadecanol (COH), and water. A decrease in the COH mole content results in increased domain size and viscosity of the water-diluted α-gel system. Additionally, when a sample is prepared by slow cooling and/or at low stirring speed, the domain size and viscosity of the water-diluted α-gel system increase.

α-Gel (α-Form Hydrated Crystal) Prepared by Eco-Friendly Cationic Surfactant.

We studied the structures and properties of gel samples prepared by mixtures of N-[3-(dimethylamino)propyl]docosanamide (APA-22) acid salt (APA-22 L-lactic acid), 1-octadecanol (COH), and water. The gel samples prepared at the mole ratios [APA-22 L-lactic acid]:COH = 1:3, 1:4, and 1:5 yielded two phases; one being the α-gel (α-form hydrated crystal) phase, incorporating a significant quantity of water between lamellar bilayers, and the other being the excess water phase. The lamellar d-spacing remained practically unaltered at these mole ratios, thus maintaining the quantity of water incorporated between the lamellar bilayers relatively constant.

Dynamic Light Scattering Measurements for Soft Materials on Solid Substrates: Employing Evanescent-wave Illumination and Dark-field Collection with a High Numerical Aperture Microscope Objective.

We developed an instrument that allows us to measure dynamic light scattering from soft materials on solid substrates by avoiding strong background due to the reflection light from substrates. In the instrument, samples on substrates are illuminated by evanescent-light field and the resultant scattered light from the samples is collected with a dark-field optical configuration by employing a high numerical aperture microscope objective. We applied the instrument to measure the dynamic properties of supported lipid bilayers (SLBs), which have been widely utilized in industries as functional materials such as biosensors.

Dynamics of Liquid Oil that Flows Inside Aqueous Wet Foam.

Wet soap foam spontaneously imbibes liquid oil without defoaming when it is brought into contact. The kinetics behind this recently observed phenomenon was studied experimentally, with focus on the origin of the suction force and on the oil front dynamics. Using an aqueous foam with an air volume fraction slightly greater than the critical value ϕ, we show that the pumping pressure of oil and/or miscible liquid into the wet foam is attributed to the interfacial distortion of the bubble surfaces.

Liquid oil that flows in spaces of aqueous foam without defoaming.

A very interesting phenomenon has been observed in which foam formed from an aqueous fatty acid potassium salt solution spontaneously absorbs liquid oil immediately upon contact without defoaming. Although this phenomenon initially appeared to be based on capillary action, it was clarified that the liquid oil that flows in foam film did not wet the air/water interface. In this study, it is discussed why aqueous foam can spontaneously soak up liquid oil without defoaming using equilibrium surface tension, dynamic oil/water interfacial tension, and image analysis techniques.

Effect of functional group on the monolayer structures of biodegradable quaternary ammonium surfactants.

The monolayer structures and conformational ordering of cationic surfactants including the biodegradable quaternary ammonium molecules have been systematically characterized by π-A isotherm, surface potential, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and sum frequency generation (SFG) vibrational spectroscopy. It was found that the monolayer of the typical dialkyl dimethylammonium on the water surface was less densely packed along with many conformational gauche defects. The packing density and ordering of these monolayers were improved as halide ions were added to the subphase.

Precipitate deposition around CMC and vesicle-to-micelle transition of monopotassium monododecyl phosphate in water.

Monoalkyl phosphate (MAP) salts are a kind of bivalent anionic surfactants. The difference of properties between half-neutralized monosalt and completely neutralized disalt is very interesting. In this study, the aggregation behavior of monopotassium monododecyl phosphate (MAP-12K) in aqueous solution with an increase in concentration was investigated by surface tension (γ), elemental analysis, gas chromatography, differential scanning calorimetry, steady-state fluorescence, and negative strained transmission electron microscopy techniques.

Effect of head groups on the phase transitions in Gibbs adsorption layers at the air-water interface.

The adsorption kinetics and the surface phase behavior of four different amphiphiles, which are 2-hydroxyethyl laurate (2-HEL), dodecanoyl N-ethanolamide (NHEA-12), dodecanoyl N-methylethanolamide (NMEA-12) and tetradecanoyl N-methylethanolamide (NMEA-14), have been investigated at the air-water interface by film balance, surface tensiometer and Brewster angle microscopy (BAM). The former two amphiphiles show a first-order phase transition from a lower density liquid like phase to a higher density condensed phase in Gibbs adsorption layers. On the other hand, the latter two amphiphiles are unable to show such characteristics under any experimental conditions.

Aquatic toxicity and biodegradability of advanced cationic surfactant APA-22 compatible with the aquatic environment.

Cationic surfactant is a chemical substance used in hair conditioner, fabric softener and other household products. By investigating the relationship between the aquatic toxicity and the chemical structures of two types of mono alkyl cationic surfactants, alkyl trimethylammonium salts and alkyl dimethylamine salts, we have found that the C22 alkyl chain length is effective to reduce the toxicity. Besides, we have recognized that the amidopropyl functional group contributes to the enhanced biodegradability by investigating the biodegradation trend of (alkylamidopropyl)dimethylamine salt (alkyl chain length: C18).

The excellent water-solubility of N-[3-(dimethyl-amino)propyl] docosanamide chloride : the most eco-friendly cationic hair conditioning agent.

A new hair-conditioning agent, N-[3-(dimethylamino)propyl]docosanamide (APA-22) hydrochloric acid salt (APA-22 HCl), has excellent solubility in water with a solubility limit over 10-times larger than that of other APA hydrochloric salts with shorter alkyl chain lengths. The physicochemical characteristics of APA-22 HCl were studied at 25 degrees C by using equilibrium surface tension (gamma), solubilization of an oil-soluble dye, steady-state fluorescence, and chloride ion selective electrode techniques. The APA-22 HCl salt is considered to form an aggregate at a concentration, C(1), which is about twice the concentration of the solubility limit of APAs with shorter alkyl chains.

Premicellar aggregation of fatty acid N-methylethanolamides in aqueous solutions.

The aggregation behaviors of an excellent nonionic foam booster, namely, fatty acid N-methylethanolamide (NMEA-X; X indicates the carbon number of the acyl group), in aqueous solutions have been studied by equilibrium surface tension (gamma), solubilization of oil-soluble dye, and steady-state fluorescence techniques. NMEA, having a longer alkyl chain than NMEA-08, clearly had two break points on the gamma versus log C (where C is concentration) curves. The solubilization of the oil-soluble dye for NMEA aqueous solutions began at the break point of higher concentration in the gamma versus log C curves, so this concentration was confirmed to be the critical micellization concentration (cmc).

Phase behavior of poly(oxyethylene) cholesteryl ether/novel alkanolamide/water systems.

The phase behavior and microstructure of mixed nonionic surfactant systems containing poly(oxyethylene) cholesteryl ether (ChEOn, n=15 and 10), a new alkanolamide-type foam booster, dodecanoyl N -methylethanolamide (NMEA-12), and water, were investigated at 25 degrees C by means of visual observation and small-angle X-ray scattering. In the ChEO(15)/water binary system, aqueous micellar (W(m)), discontinuous cubic liquid crystal (I(1)), hexagonal (H(1)), rectangular ribbon (R(1)), lamellar (L(alpha)), and solid (S) phases are successively formed with increasing surfactant concentration. Although the R(1) phase is an intermediate phase formed in a very narrow composition range in conventional surfactant systems, its domain is unusually wider than that of H(1), which may be attributed to the packing constraint caused by the bulky cholesteric group in the lipophilic core of the aggregate.

Phase diagrams and microstructure of aggregates in mixed ionic surfactant/foam booster systems.

The phase behavior and microstructure of surfactant systems containing a new alkanolamide-type foam booster, dodecanoyl N-methyl ethanolamide (NMEA-12), were investigated by means of phase study and small angle X-ray scattering. Different from other similar alkanolamides, NMEA-12 possesses a low melting point and forms a lyotropic liquid-crystalline phase (L(alpha) phase) at room temperature. This is attributed to the attached methyl group, which increases the fluidity of the molecule.