The role of the cosurfactant in the CTAB/water/n-pentanol/n-hexane system: Pentanol effect on the phase equilibria and mesophase structure

Abstract

We report on the effect of 1-pentanol loading on the phase behaviour of mixtures of CTAB/water/n-hexane at fixed mole ratios 1:80:47. The cosurfactant induces changes in the interfacial film curvature. By increasing the pentanol/CTAB mole ratio, the system evolves from oil-in-water to water-in-oil structures. For very large 1-pentanol loading some water is expelled from the reverse micelles resulting in a L(2) plus water equilibrium (emulsification failure). In the range of compositions investigated most of the phase equilibria reveals the coexistence of liquid crystals and hexane/pentanol solutions. In these cases, we estimate the interface composition by assuming a constant 1-pentanol concentration in all the oil domains, and by tacking into account the alcohol solubility in water. In the case of single-phase sample the interfacial composition was determined by means of turbidimetric titration. The adsorption of cosurfactant at the interface of direct micelles, planar lamellae, bicontinuous microemulsions, and spherical reverse micelles follows the same adsorption isotherm (independently from the curvature of the interface). Moreover, the results obtained unambiguously show that the interface composition dictates the spontaneous curvature of interfacial film. Actually positive, null, and negative curvatures correspond to different compositions of the interfacial film. Once the influence of cosurfactant on the spontaneous curvature of the interface is understood, the appearance of the emulsification failure upon pentanol loading can be rationalised within the framework of the flexible surface model

Phase behavior, interfacial composition and thermodynamic properties of mixed surfactant (CTAB and Brij-58) derived w/o microemulsions with 1-butanol and 1-pentanol as cosurfactants and n-heptane and n-decane as oils

“…Bayrak [32] has used the method on nonionic surfactant stabilized systems. Recently, Palazzo et al [33,34] have determined the interfacial compositions of CTAB/n-hexane/1-pentanol/water w/o microemulsion system using the dilution method and found satisfactory agreement with those obtained by using the pulsed gradient spin-echo NMR (PGSE-NMR) technique.…”

“…3 represents the phase diagram of CTAB/Pn/Hp/water under identical compositions at 303 K wherein lesser amount of alkanol was required to form single-phase microemulsion than Bu. At higher weight fraction of Pn, a second biphasic region appeared [denoted by EF (emulsification failure [34]) in the phase diagram]. Such EF did not occur with Bu in the system.…”

“…This indicated that the lower phase was a w/o microemulsion in equilibrium with an upper oleic phase, which might contain Bu solubilized in it. Earlier Palazzo et al [34] identified a biphasic region at a low cosurfactant content in CTAB/n-hexane/1-pentanol/water microemulsion system. Diffusion coefficient study with the aid of 1 H NMR studies revealed that the upper phase was the oil phase with trace amount of Pn dissolved in it and the lower phase was a oil swollen normal micellar solution.…”

The effect of structure of oil phase, surfactant and co-surfactant on the physicochemical and electrochemical properties of bicontinuous microemulsion

“…Among the 40 combinations that were selected, 12 systems did not lead to a stable microemulsion at room temperature (Tables 1-3). There appears to be a compatibility requirement between the chain length of the oil phase (alkane) and the chain length of the cosurfactant [28]. Among the linear alkanes stable bicontinuous microemulsions were formed up to tetradecane with n-butanol as a co-surfactant.…”

High-resolution NMR spectroscopy of encapsulated proteins dissolved in low-viscosity fluids

“…A variety of mechanisms are available in aqueous solution to induce the partial alignment necessary to reintroduce dipolar couplings. As mentioned above, the phase diagram of reverse micelle surfactants is complex and contains regions where small reverse micelles suitable for NMR and liquid crystalline components co-exist [12, 57]. In addition, there are regions of the phase diagram for protein-containing reverse micelles where the particles are non-spherical and can have an inherent anisotropic magnetic susceptibility [26].…”