Effect of Large Changes in Temperature and Pressure on the Thermodynamic Properties of Micellization and on the Distribution Constant of a Polar Solute in Micellar Solutions

Abstract

Density measurements of pentanol (PentOH)-dodecyltrimethylammonium bromide (DTAB)-water mixtures as functions of both alcohol and surfactant (m S ) concentrations were carried out at 0.1 MPa from 45 to 75°C and at 19 MPa from 25 to 130°C. The standard (infinite dilution) partial molar volumes and expansibilities of DTAB in water and the corresponding properties in the micellar phase were calculated from the experimental data. As far as PentOH in DTAB micellar solutions is concerned, with the exception of the standard partial molar volume (V°R) data at 130°C and 19 MPa, all the V°R Vs m S trends are monotonic curves with m S . The data of V°R as a function of m S were treated by means of an equation previously used for data obtained at ambient conditions. So it was possible to evaluate simultaneously the distribution constant (K) of PentOH between the aqueous and micellar phases and the standard partial molar volume of alcohol in the aqueous (V°R ,f ) and the micellar (V°R ,m ) phases. The standard free energy of transfer (∆G°t) of PentOH from the aqueous to the micellar phases was calculated from K values. By using experimental literature data for the present system at 25°C, ∆G°t values as functions of temperature and pressure were calculated. The very good agreement between the simulated and experimental values indicates that the model used also holds at higher temperatures. Equations correlating the standard free energy, enthalpy, and entropy of transfer to temperatures up to 130°C and pressures up to 19 MPa were proposed.

Calorimetric Study of the Micellization of Alkylpyridinium and Alkyltrimethylammonium Bromides in Water

“…In the premicellar region, H h 2 was expressed in terms of the temperature derivative of the surfactant's mean activity coefficient γ ( , described by the Guggenheim's approximation. 4,5,19,20 For all the measured surfactants the critical micelle concentrations determined by employing Philips criter-ion 21,22 on the experimental titration curves agree well with the corresponding values obtained by other methods. 11,12,23 Fitting of the simulated calorimetric titration curves to those determined experimentally showed that the applied fitting procedure can provide only ∆H M values while it is not able to give any information on the micelle ionization parameter p/n.…”

Thermodynamics of Micellization of Sodium Alkyl Sulfates in Water at High Temperature and Pressure

“…As far as NaDS is concerned, at 25 °C and 19 MPa as well as at 65 °C and both pressures, ( V Φ ,S − ) increases monotonically with m S in the whole range of m S studied, and therefore, the cmc is not evident (Figures and ). NaDS behaves similarly to dodecyltrimethylammonium bromide (DTAB); however, for the latter the cmc values were always detected.…”

“…In the following, we shall focus our attention on and on the pressure effect on it since studying the temperature coefficient of is equivalent to studying the pressure coefficient of As observed for DeTAB 11 and DTAB, of each surfactant is positive and slightly decreases with pressure. Due to the lack of values for NaDS, we can compare only NaDeS to DeTAB.…”

“…Apparent molar volume and adiabatic compressibility of fluorinated and hydrogenated surfactants in water were determined in the range of 0.1−80 MPa and 5−35 °C. , Vikingstad et al studied the effect of large change of pressure (1−160 MPa) on the partial molar volume and adiabatic compressibility of sodium decanoate in water. Volumetric studies of DeTAB and dodecyltrimethylammonium bromide in water from 25 to 130 °C and from 0.1 to 19 MPa were carried out. , As a general result, the intensive variables influence the thermodynamic properties of micellization but their role is not straightforward.…”

Mixed Monolayers Self-Assembled on Mica Surface

“…The concentration of DTAB, c DTAB , in solutions varied from 0.3 to 10 mM, whereas the time of adsorption changed from 30 to ca. 20 h. To avoid adsorption of micelles on mica, c DTAB was maintained below its critical concentration of micellization (cmc), that is, below 0.0154 M at 20 °C …”