New adsorption model -- theory, phenomena and new concept.

According to the conventional Gibbs adsorption model, which is a common assumption about the molecular concentration at surfaces, the adsorbed film of soluble amphiphiles is located at the air/solution interface just like Langmuir monolayer which is illustrated in many physical chemistry text books on "Colloid and Interface Science". According to many proofs of the experimental results here, the newer idea for the surface adsorption is confirmed and explained, which is quite different from the conventional Gibbs surface excess model at the air/solution interface.

Molecular dynamics investigation on adsorption layer of alcohols at the air/brine interface.

Alcohols are a significant group of surfactants which have been employed extensively in industry to improve the interfacial effects. Recently, the change in surface potential (ΔV) of two isomeric hexanols, methyl isobutyl carbinol (MIBC) and 1-hexanol, was investigated by using an ionizing (241)Am electrode. It clearly showed the opposite effects between MIBC and 1-hexanol in the interfacial zone: one enhanced the presence of cations, whereas the other enhanced the presence of anions.

Solubilization of n-alkylbenzenes into gemini surfactant micelles in aqueous medium.

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, and n-pentylbenzene into micelles of decanediyl-1-10-bis(dimethyltetradecylammonium bromide) (14-10-14,2Br(-)) has been investigated in the temperature range from 288.2 to 308.2 K.

Surface potential of 1-hexanol solution: comparison with methyl isobutyl carbinol.

Alcohols have an amphiphilic characteristic and are employed in industrial processes to enhance interfacial properties. In this study, the change in surface potential (ΔV) and surface tension of 1-hexanol were measured on the subsurface of electrolyte solutions (NaCl at 0.02, 0.

Surface potential of methyl isobutyl carbinol adsorption layer at the air/water interface.

The surface potential (ΔV) and surface tension (γ) of MIBC (methyl isobutyl carbinol) were measured on the subphase of pure water and electrolyte solutions (NaCl at 0.02 and 2 M). In contrast to ionic surfactants, it was found that surface potential gradually increased with MIBC concentration.

Examination of surface adsorption of cetyltrimethylammonium bromide and sodium dodecyl sulfate.

Several pieces of experimental evidence of condensation of soluble surfactant molecules, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), into the air/water surface region from the bulk solution are presented at different added salt concentrations in order to substantiate that the concentrated molecules do not locate just at the air/solution interface. The insoluble monolayer just at the air/subphase interface for the two surfactants could be studied by surface pressure (π) versus molecular surface area (A), surface potential (ΔV) versus the area (A), infrared absorption of the surface region, and BAM (Brewster angle microscope) image. From surface tension versus concentration curves for the two surfactant solutions, the apparent molecular surface area and the cmc values were determined at different added salt concentrations, and the degree of counterion binding to micelle was found to be 0.

Solubilization of n-alkylbenzenes into decanoyl-N-methylglucamide (Mega-10) solution; temperature dependence.

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, and n-hexylbenzene into micelles of decanoyl-N-methylglucamide (Mega-10) was studied at 303.2, 308.2, 313.

Difference in Surface Properties between Insoluble Monolayer and Adsorbed Film from Kinetics of Water Evaporation and BAM Image.

The evaporation rate of water molecules across three kinds of interfaces (air/water interface (1), air/surfactant solution interface (2), and air/water interface covered by insoluble monolayer (3)) was examined using a remodeled thermogravimetric balance. There was no difference in both the evaporation rate and the activation energy for the first two interfaces for three types of surfactant solutions below and above the critical micelle concentration (cmc). This means that the molecular surface area from the Gibbs surface excess has nothing to do with the evaporation rate.

Hydrolysis of ionized deoxycholic acid in the aqueous phase and rate analysis for transfer of neutralized deoxycholic acid into the benzene phase across the benzene/water interface.

Sodium deoxycholate in water dissociates into sodium cation and deoxycholate anion in the aqueous phase, and then, the latter anions partially hydrolyze to form deionized deoxycholic acids. The acids move into the benzene phase, when liquid benzene is placed upon the aqueous phase, and finally the partition equilibrium is reached. The above processes were traced by pH change in the aqueous phase by a pH meter or the change in [OH-] with time, from which the rate for transfer of neutralized acid to the organic phase was analyzed.

Solubilization of n-alkylbenzenes into decanoyl-N-methylglucamide (Mega-10) solution.

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, and n-hexylbenzene into micelles of decanoyl-N-methylglucamide (Mega-10) was studied, where equilibrium concentrations of the above solubilizates were determined spectrophotometrically at 303.2 K. The concentration of the above solubilizates remained constant below the critical micelle concentration (cmc) and increased linearly with an increase in Mega-10 concentration above the cmc.

Water evaporation rates across hydrophobic acid monolayers at equilibrium spreading pressure.

The effect of alkanoic acid [CH(3)(CH(2))(n-2)COOH; HCn] and perfluoroalkanoic acid [CF(3)(CF(2))(n-2)COOH; FCn] monolayers on the water evaporation rate was investigated by thermogravimetry tracing the decrease in amount of water with time. The evaporation rate from the surface covered by a monolayer was measured as a function of temperature and hydrophobic chain length of the acids, where the monolayer was under an equilibrium spreading pressure. From thermal behavior of the crystallized acids, their solid states are C-type in crystalline state over the temperature range from 298.

Langmuir monolayer properties of perfluorinated double long-chain salts with divalent counterions of separate electric charge at the air-water interface.

The novel perfluorinated double long-chain salts with divalent counterions of separate electric charge, 1,1-(1,omega-alkanediyl)-bispyridinium perfluorotetradecane- carboxylate [CnBP(FC14)2 : n = 2, 6, 10, 14], were newly synthesized and their interfacial behavior was investigated by Langmuir monolayer methods. Surface properties [surface pressure (pi)-, surface potential (DeltaV)-, dipole moment (micro perpendicular)-area (A) isotherms] and morphological images of CnBP(FC14)2 monolayers on a subphase of water and on various NaCl concentrations were measured by employing the Wilhelmy method, the ionizing electrode method, fluorescence microscopy (FM), and Brewster angle microscopy (BAM). CnBP(FC14)2 formed a stable monolayer on water at 298.

Solution properties of perfluorinated anionic surfactants with divalent counterion of separate electric charges.

Novel surfactants of perfluorinated double long-chain salts with divalent counterion of separate electric charge, 1,1-(1,omega-alkanediyl)bispyridinium diperfluorononanoate (CnBP(FC9)2, n = 2, 4, 6, 8) were newly synthesized. Their solution properties were investigated by surface tension measurement over the temperature range from 298.2 to 313.

Solubilization of n-alkylbenzenes into octaethylene glycol mono-n-tetradecyl ether (C14E8) micelles.

Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, and n-pentylbenzene into the micelles of octaethylene glycol monotetradecyl ether (C(14)E(8)) was studied, where equilibrium concentrations of all the solubilizates were determined spectrophotometrically at 298.2, 303.2, and 308.

Thermodynamic study on competitive solubilization of cholesterol and beta-sitosterol in bile salt micelles.

Differences in the preferential solubilization of cholesterol and competitive solubilizates (beta-sitosterol and aromatic compounds) in bile salt micelles was systematically studied by changing the molar ratio of cholesterol to competitive solubilizates. The cholesterol solubility in a mixed binary system (cholesterol and beta-sitosterol) was almost half that of the cholesterol alone system, regardless of the excess beta-sitosterol quantity added. On the other hand, the mutual solubilities of cholesterol and pyrene were not inhibited by their presence in binary mixed crystals.

Pyrene fluorescence at air/sodium dodecyl sulfate solution interface.

The dependence of pyrene fluorescence spectra on the concentration of sodium dodecyl sulfate (SDS) was observed, where the solution was prepared from water saturated with pyrene. The values of the I(1)/I(3) ratio from the bulk solution and from the upper meniscus region in an optical cell were similar but decreased rapidly around the critical micelle concentration (cmc) of SDS, indicating that pyrene molecules preferred to be solubilized in the micelles having a lower dielectric constant. The fluorescence intensity of the excimer indicated the concentration of pyrene molecules at the air/solution interface or the surface activity of pyrene molecules.

Micellization of conjugated chenodeoxy- and ursodeoxycholates and solubilization of cholesterol into their micelles: comparison with other four conjugated bile salts species.

Micelle formations of sodium glyco- and taurochenodeoxycholate (NaGCDC and NaTCDC) and sodium glyco- and tauroursodeoxycholates (NaGUDC and NaTUDC) was studied at 308.2 K for their critical micelle concentrations at various NaCl concentrations by pyrene fluorescence probe, and the degree of counterion binding to micelle was determined using the Corrin-Harkins plots. The degree of counterion binding was found to be 0.

Examination of surface adsorption of sodium chloride and sodium dodecyl sulfate by surface potential measurement at the air/solution interface.

The surface potential (DeltaV) of the air/sodium chloride solution interface was measured by using an ionizing (241)Am electrode method at 298.2 K. The surface potential steeply increased from 0 up to 15 mV with increasing concentration, then gradually increased up to 20 mV between 1 and 10 mmol dm(-3), and finally stayed almost constant at 20 mV up to the concentration of 20 mmol dm(-3).

Evaporation from water-ethylene glycol liquid mixture.

Evaporation rates were determined for water-ethylene glycol liquid mixtures with different mole fractions, where the evaporation rate expressed as mg min(-1)/area was used because of the presence of two kinds of molecular species. The rate increased with increasing temperature and decreased with increasing mole fraction of ethylene glycol, almost obeying ideal mixing of the two components, although a small positive deviation was observed over the mole fraction from 0 to 0.5 of ethylene glycol at higher temperatures.

Investigation of the interaction between sodium dodecyl sulfate and cationic polymers.

Aggregation properties of sodium dodecyl sulfate (SDS) on a cationic hydroxyethyl cellulose, Polyquaternium-10 (PQ-10), of low charge density were studied by potentiometric and pyrene fluorescence methods and compared with those of poly(diallyldimethylammomium chloride) (PDADMAC) of high charge density. The critical aggregation concentration (cac) was measured with the potentiometric method and further confirmed with the fluorescence method. The former was found to be more accurate.

Micelle formation of N-(1,1-dihydroperfluorooctyl)- and N-(1,1-dihydroperfluorononyl)-N,N,N-trimethylammonium chlorides.

Micelle formation of N-(1,1-dihydroperfluorooctyl)-N,N,N- and N-(1,1-dihydroperfluorononyl)-N,N,N-trimethylammonium chloride was investigated by analyzing the concentration dependence of the electric conductivity and of the activity of the counterion (Cl(-)) of the solution. The three micellization parameters for ionic surfactants, the micellization constant K(n), the micelle aggregation number n, and the number of counterions per micelle m, were determined by combination of electric conductivity and counterion concentration. The present analysis employed two slopes of the plots of specific conductivity against surfactant concentration below and above the critical micelle concentration and the mass action model of micelle formation.

Solubilization of n-alkylbenzenes in aggregates of sodium dodecyl sulfate and a cationic polymer of high charge density (II).

The solubilization property of the aggregate composed of sodium dodecyl sulfate (SDS) and a cationic polymer (polydiallyldimethylammonium chloride, PDADMAC) was investigated. From the binding isotherm, the increasing free SDS concentration (Cf) above the critical aggregation concentration (cac) was clearly confirmed and used to calculate the Gibbs free energy change of solubilization. The maximum additive concentration of the alkylbenzene solubilizates remained almost constant around their aqueous solubilities below the cac and then increased with increasing SDS concentration above the cac and with decreasing alkyl chain length of the solubilizates.

Solubilization study for aggregates of sodium dodecyl sulfate and cationic polymer of high charge density.

Interaction of sodium dodecyl sulfate (SDS) with a cationic polymer (polydiallyldimethylammonium chloride, PDADMAC) was investigated. The surface tension of SDS/PDADMAC solution ([PDADMAC]=100 ppm) decreased from 72 to ca. 40 mN m(-1) with increasing SDS concentration at 298.

Study on water evaporation through 1-alkanol monolayers by the thermogravimetry method.

The influence of 1-alkanol monolayers on the rate of water evaporation has been studied by measuring water loss per unit time using thermogravimetry. The evaporation rate of water from the surface covered by an insoluble monolayer for each of four saturated 1-alkanols (C(13)OH, C(15)OH, C(17)OH, and C(19)OH) was measured as a function of temperature and alkyl chain length, where the monolayer was under equilibrium spreading pressure. The evaporation rate decreased with increasing alkyl chain length or increasing molecular interaction among 1-alkanol molecules in the insoluble monolayer.

Micelle formation of sodium chenodeoxycholate and solubilization into the micelles: comparison with other unconjugated bile salts.

Micellization of sodium chenodeoxycholate (NaCDC) was studied for the critical micelle concentration (CMC), the micelle aggregation number, and the degree of counterion binding to micelle at 288.2, 298.2, 308.