Thermodynamic Properties of Cetyltrimethylammonium Bromide in Ethanol-Water Media With/without the Presence of the Divalent Salt

The physicochemical properties of cetyltrimethylammonium bromide (CTAB) in pure water and ethanol-water mixtures in the presence and absence of MnSO₄.6H₂O were studied by measuring the conductivity at room temperature. The concentration range of CTAB was ~1.00 × 10^-5 M to ~1.00 × 10^-2M and the concentration of MnSO₄.6H₂O was 0.001 M, 0.005 M, 0.01 M. With increasing ethanol content in the solvent composition, the critical micelle concentration (CMC) and the degree of micellar dissociation (α) of CTAB increased. With the help of CMC and α, the standard free energy of micellization (ΔG _m ^ο ) was evaluated. With an increase in ethanol content, the negative values of ΔG _m ^ο decreased. CTAB micellization was tested in the context of specific solvent parameters. The solvent conductivity ratio at CMC to limiting conductivity was employed as a solvophobic influence. The addition of salt (MnSO₄.6H₂O) decreases the CMC of CTAB due to the screening of the electrostatic repulsion of the head groups. Here, we report that micellization is strongly influenced by salt concentration.

The Quantitative Characterization of Chemical Modification of Sodium Dodecyl Sulphate Micellar Solutions and Retention Model in Micellar Liquid Chromatography

The micelle solutions of sodium dodecyl sulphate (NaDS) modified by simultaneously presence of different aliphatic alcohols and an inorganic salt have been quantitatively characterized by the values of critical micelle concentrations, the degrees of counter-ion binding and electrostatic potentials of surface. The obtained characteristics of hybrid micelles and the coefficients of modifier distribution between aqueous solution and micellar pseudophase were used to develop a conceptual retention model in micellar liquid chromatography (MLC). The new retention model takes into account the microenvironment changes of an analyte when it goes from the hybrid micellar eluent to a modified surface of alkyl-bounded sorbent.

Volumetric and Surface Properties of Short Chain Alcohols in Aqueous Solution-Air Systems at 293 K

From measurements of the surface tension, density, viscosity and light scattering of aqueous solutions of methanol, ethanol and propanol at 293 K, their activity in the surface monolayer, surface excess concentration, and apparent and partial molar volume were determined. The surface excess concentration of alcohols at the water–air interface was determined from the Gibbs equation by using both the alcohol's activity and their molar fraction in the bulk phase and recalculated by using the Guggenheim–Adam equation. The values of the surface excess concentration determined from the Gibbs equation were also applied to determine the standard Gibbs energy of alcohol adsorption at the water–air interface from Langmuir’s equation and compared to those determined from that of Aronson and Rosen.

Microstructural study of cetyltrimethylammonium bromide / 1-butanol / salt / water system — SANS and 2D-NOESY analysis

Interaction of 1-butanol (BuOH) with a cationic surfactant, cetyltrimethylammonium bromide (CTAB) aggregate, in water and salt solution has been studied by viscometry, small-angle neutron scattering (SANS), and 2D-NMR techniques. The experimental results are interpreted in terms of a possible micellar growth occurring in the presence of added alcohol and salt. It was observed that the addition of BuOH strongly influences the viscosity of the CTAB/salt micellar system, reaching a peak viscosity at about 0.5% w/v of BuOH over a range of salt concentrations. Scattering measurements support the idea of a structural transformation by the observation of a spectral shift (broadening) as the total concentration of surfactant varies, indicating a decrease in the intermicellar distance and narrow size distribution. The chemical shift from 1H NMR measurements gave complementary data on the solubilization of BuOH in CTAB micelles, whereas the expected locus (site) of the additive added to the surfactant including the dynamics of the molecules in micellar aggregates were successfully correlated by significant and positive cross peaks obtained from two-dimensional nuclear Overhauser effect spectroscopy (2D-NOESY).

Dynamic light scattering studies of additive effects on the microstructure of aqueous gemini micelles

Dynamic light scattering (DLS) measurements have been performed at 30 degrees C to see the effects of additives on the microstructure of gemini alkanediyl-alpha,omega-bis(dimethylcetylammonium bromide) surfactants, (Br-, n-C16H33N+Me2-(CH2)s-Me2- N+n-C16H33, Br-, 16-s-16, where s = 4, 5, 6). In pure aqueous solutions, the hydrodynamic diameter, Dh, was found to increase rapidly with geminis in comparison to their monomeric counterpart cetyltrimethylammonium bromide (n-C16H33N+Me3, Br-, CTAB) on increasing surfactant concentration. The additives considered in the present study are n-alcohols (C4-C6OH) and n-hexylamine (C6NH2) on the micellar growth of 0.03 M 16-4-16 in the presence and absence of 0.001 M KBr. The presence of 0.001 M KBr or organic additives at lower concentrations singly or jointly has little effect on the micellar size. As the chain length of the additive increases, the size increases with the increase of additive concentration, the magnitude being substantial in the presence of 0.001 M KBr. However, for equal chain length additives (C6OH, C6NH2), the effect was greater for C6OH. In case of C6NH2, the value of Dh reaches to almost constancy when the concentration of the additive was increased. Increased effectiveness of additives in the presence of added salt (KBr) is discussed in light of electrostatic and hydrophobic forces operating in the solution, which are always responsible for growth processes.

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.