Louis-Charles de Ménorval

Interactions of phenol with cationic micelles of hexadecyltrimethylammonium bromide studied by titration calorimetry, conductimetry, and 1H NMR in the range of low additive and surfactant concentrations

Interactions of phenol (PhOH) with micellar aggregates of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions at surfactant concentrations close to the CMC and phenol contents of 1, 5, or 10 mmol kg(-1) have been investigated at 303 K by means of titration calorimetry, solution conductimetry, and (1)H NMR spectroscopy. Estimates of the main thermodynamic parameters related to HTAB micellization were made for PhOH/HTAB/H(2)O systems based on the specific conductivity measurements and calorimetric determination of the cumulative enthalpy of dilution as functions of the surfactant concentration at a fixed additive content. The combined analysis of the results obtained in H(2)O solutions pointed to the preferential location of PhOH in the outer micelle parts by an enthalpy-driven mechanism. Additional PhOH molecules were located increasingly deeper within the micelle core. The (1)H NMR study of PhOH solubilization by 1.5 mmol kg(-1) HTAB solutions in D(2)O indicated that the two categories of the solubilization site became saturated with the solubilizate already at the lowest additive content. Dissimilar amounts of the solubilized material in H(2)O and D(2)O solutions were ascribed to the difference in the initial micelle structures formed in the two solvents, as inferred from calorimetry and (1)H NMR studies of the HTAB micellization in D(2)O and H(2)O.

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.

Aluminium-derivatized silica monodisperse nanospheres by a one-step synthesis-functionalization method and application as acid catalysts in liquid phase

Aluminium-derivatized submicron-in-size silica spheres (Al-MSS), with controllable morphology, particle size, mesoporosity, and incorporation of an active phase at the internal surface, have been prepared by a one-step synthesis-functionalization method in view of potential applications in the liquid phase. Four Al-MSS samples were prepared with a molar Si/Al ratio in the initial gel of 44, 22, 11, and 7, and their properties were compared with those of a purely siliceous sample (MSS). Nitrogen adsorption, XRD, SEM and TEM studies revealed homodispersed particles with average diameters ranging between 350 and 520 nm and possessing radial porosity. BET specific surface areas were included between 900 and 1300 m2 g−1 and the average pore diameter varied from 3 to 3.4 nm. Surface reactivity and Al accessibility at the material surface were determined with measurements of two-cycle ammonia adsorption and EDX-based calculations. The best compromise between textural parameters, surface properties, and stoichiometric Al incorporation was achieved with Al-MSS-22. This sample was further characterized by 129Xe-NMR, 27Al-MAS-NMR, XPS, NH3-TPD and IR methods to confirm the high accessibility of its internal porous structure and the presence of weak Bronsted and strong Lewis acid sites on its surface. The catalytic behavior of Al-MSS-22 in the liquid phase was tested in esterification reactions of ethanoic acid with alcohols or polyols such as butanol, isoamyl alcohol, ethylene glycol, and glycerol. In the case of alcohols, the remarkable performance of this aluminosilicate was supported by conversion rates close to 100%, allowing the amount of the catalytic material to be significantly decreased compared with other systems already tested in the literature.

Competitive interactions between components in surfactant-cosurfactant-additive systems.

Complex interactions of phenol (PhOH), heptanol (HeOH) and heptanoic acid (HeOIC) with micellar aggregates of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions at surfactant concentrations close to the CMC, HeOH or HeOIC content of 0.5 mmol kg(-1), and phenol molality 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 analysis of the composition-dependence of the (1)H chemical shifts assigned to selected protons in the surfactant and additive units revealed the location of PhOH both within the hydrophobic micelle core and in the vicinity of the quaternary ammonium groups, the phenol penetration being somewhat deeper in the presence of HeOIC. The phenomenon was globally more exothermic with increasing extent of PhOH solubilization and it was accompanied by a gradual decrease in the positive entropy of micellization. The solubilization was competitive for high phenol contents in the aqueous phase, with some HeOH and HeOIC units being displaced progressively towards the aqueous phase.