Miscibility of Butanol and Cationic Surfactant in the Adsorbed Film and Micelle

Rhamnolipids Production by a Pseudomonas eruginosa LBI Mutant: Solutions and Homologs Characterization

This paper evaluates the effect of additives (NaCl and ethanol) on the solution properties of rhamnolipids. The properties are the surface activity, aggregate formations and emulsifying activity as well as the synergistic effects of additives and pH variations on the physical properties of rhamnolipids. Additionally, analysis of fatty acids and rhamnolipid homologues produced using different carbon sources was performed by mass spectrometry. The results indicate that this biosurfactant maintain its properties in the presence of additives. NaCl decreases the size and number of aggregates formed in solutions without pH control, while ethanol to rhamnolipid solutions reduces critical micelle concentration and favors aggregation of monomers. The profiles of fatty acids produced by P. aeruginosa LBI 2A1 varied according to the carbon source used, however for rhamnolipids there was no difference.

Characterization and encapsulation efficiency of rhamnolipid vesicles with cholesterol addition

The effect of cholesterol on the vesicle formation of a rhamnolipid biosurfactant extracted from the liquid culture of Pseudomonas aeruginosa SP4 was investigated. The rhamnolipid vesicles were prepared in a phosphate-buffer saline (PBS) solution (pH 7.4) at a biosurfactant concentration of 2.6mM, or 6.5 times the critical micelle concentration (CMC), with various amounts of cholesterol. The biosurfactant solution was characterized using turbidity, zeta potential, and dynamic light scattering (DLS) measurements. The morphology of the rhamnolipid vesicles formed at different cholesterol concentrations was examined with the use of transmission electron microscopy (TEM). The results showed that the rhamnolipid biosurfactant formed spherical vesicles both in the absence and presence of cholesterol, but the incorporation of the cholesterol into the bilayer membrane reduced the vesicle size. Sudan III, a water-insoluble dye, was used as a model hydrophobic compound in the encapsulation experiment. The encapsulation efficiency (E%) of the rhamnolipid vesicles was affected by the cholesterol concentration and the initial Sudan III concentration. The maximum E% of nearly 90% was achieved at the cholesterol concentration of 100μM and the initial Sudan III concentration of 8.8μM.

Surface behavior of Triton X-165 and short chain alcohol mixtures

In this Article, the surface behavior of mixtures of nonionic Triton X-165 (TX-165) with methanol, ethanol, and propanol at constant Triton X-165 concentration in the range from 1 x 10(-7) to 10(-3) M in aqueous solutions was investigated by surface tension measurements of their solutions in a wide range of alcohol concentrations. The obtained values of the surface tension of solutions were compared with those calculated from Szyszkowski, Connors, and Fainerman and Miller equations. On the basis of the surface tension data, the Triton X-165 and alcohol concentrations at water-air interface and their standard free energy of adsorption as well as the composition of the monolayer at this interface were determined. Taking into account this composition and activity coefficient of Triton X-165 and alcohol, the free enthalpy of their mixing was also calculated. From the measurements and calculations, it results, among other things, that unexpectedly the Fainerman and Miller equation derived for ideal mixtures of homologous surfactant can be useful for the description of changes of the solution surface tension of the investigated mixtures and that the amount of short chain alcohols at the water-air interface at their low concentration in the bulk phase is proportional to the activity coefficient.

Competitive solubilization of phenol by cationic surfactant micelles in the range of low additive and surfactant concentrations

Competitive interactions of phenol (PhOH) with micellar aggregates of hexadecyltrimethylammonium bromide (HTAB) against 1-butanol (BuOH) in aqueous solutions at surfactant concentrations close to the critical micelle concentration (CMC), BuOH concentration of 0.5 mmol kg(-1), and phenol contents of 1, 5, or 10 mmol kg(-1) have been investigated at 303 K by means of (1)H NMR spectroscopy, titration calorimetry, and solution conductimetry. The solubilization loci for phenol were deduced from the composition-dependence of the (1)H chemical shifts assigned to various protons in the surfactant and additive units. Since in pure HTAB solutions phenol is already in competition with Br(-), addition of 1 mmol kg(-1) NaBr to the system weakens the phenol competitiveness. The presence of butanol in the HTAB micelles causes phenol to penetrate deeper toward the hydrophobic micelle core. For higher phenol contents, the butanol molecules are constrained to remain in the bulk solution and are progressively replaced within the HTAB micelles by the aromatic units. The competitive character of phenol solubilization against butanol is well supported by changes in the thermodynamic parameters of HTAB micellization in the presence of both of the additives.

Negative azeotropy in mixed adsorption of hexanol and dodecylammonium chloride at water/air interface

Miscibility of hexanol and dodecylammonium chloride (DAC) in adsorbed films and micelles was investigated by evaluating the compositions of the adsorbed films and micelles from surface tension measurements. Judging from the phase diagram of adsorption, negative azeotropy of adsorption was observed for the mixed adsorption of hexanol and DAC at water/air interfaces. The nonideal mixing in the adsorbed film was clarified using excess functions of adsorption. Interaction between hexanol and DAC in the adsorbed film was compared with that between other alkanols and surfactants. It was found that the range of azeotropes is narrower for the hexanol-DAC mixture than for the heptanol-octylsulfinylethanol mixture, because interaction between different species in an adsorbed film is weaker in the former than in the latter.

Effect of alcohol addition to the aqueous phase on the thermal effects of micellization of cationic benzyldimethyldodecylammonium bromide and its adsorption onto porous and nonporous silicas

Titration calorimetry has been used to study the effect of the addition of two primary alcohols, 1-butanol and 1-heptanol, to the aqueous phase on the thermal effects of micellization of benzyldimethyldodecylammonium bromide (BDDAB) as well as its adsorption onto nonporous Spherosil XO15M and onto porous aluminosilicate SiAl32d22 possessing uniformly sized mesopores. A linear decrease of the critical micelle concentration (CMC) of the cationic surfactant with the additive content was inferred from the specific conductivity measurements. All adsorption and calorimetry experiments were carried out at 298 K and at a fixed alcohol content (0.01 mol kg(-1)) either in deionized water or in a 0.01 mol kg(-1) NaBr solution. Dilution calorimetry measurements allowed determination of the cumulative molar enthalpy changes and a new analysis of these data was proposed to calculate easily the enthalpy of micellization per mole of BDDAB, Delta(mic)h, and the CMC value. The alcohol addition was shown to render the micellization phenomenon more exothermic, the effect being larger as the chain length of alcohol increased. These effects were attributed to the location of alcohol molecules between the surfactant units, their hydroxyl groups close to the surfactant head-groups, in competition with the surfactant counterions. The individual isotherms of alcohol and surfactant adsorption onto XO15M and SiAl32d22 were determined. The plots of the pseudo-differential molar enthalpy of displacement, Delta(dpl)h, against the surface coverage by the surfactant cation, Theta(BDDA+), were derived from the titration calorimetry data. The formation of surface-bound aggregates was thought to be a prerequisite for alcohol coadsorption at the solid-solution interface. At least two different types of adsolubilization sites were postulated, one of the sites being the same as in micelles and the other related to the contact area between the hydrophobic surfactant tails and the equilibrium bulk solution. Coadsorption (adsolubilization) of alcohol molecules at such sites was found to increase the exothermic contribution to the enthalpy of displacement per mole of the BDDA+ adsorbed.