Ultralow interfacial tensions in water–n-alkane–surfactant systems

Abstract

The interfacial tensions between water- and oil-rich phases in the presence of microemulsions have been measured for ternary systems of water, n-alkanes, and nonionic alkylpolyglycolether surfactants (CiEj). It is found that the minimum of the interfacial tension curve, which is observed for each system in conjunction with the well-known phenomenon of phase inversion, depends sensitively, but systematically, on the chemical nature of the oil and the surfactant. Specifically, the minimum value of the interfacial tension σ̄ab decreases by 1 order of magnitude on decreasing either the carbon number of the alkane k by 6, or the number of oxyethylene groups j by 3, or by increasing the number of carbon atoms in the surfactant tail i by 2. The numerical values of the interfacial tensions as a function of temperature are presented along with an empirical description previously suggested [R. Strey, Colloid and Polymer Sci. 272, 1005 (1994)]. From the analysis, in terms of bending energy one obtains estimates for the bending and saddle-splay constants. The similar shape of the interfacial tension curves permits a superposition of the data for all 19 systems in support of a scaling relation recently derived [S. Leitao, A. M. Somoza, M. M. Telo da Gama, T. Sottmann, and R. Strey, J. Chem. Phys. 105, 2875 (1996)]. Furthermore, we note a striking coincidence of the numerical values of critical amplitude ratio R=σ0ξ02=0.37 kT in near-critical systems and the product σ̄abξ̄2=0.44(±0.10) kT where ξ̄ is the maximum length scale in the bicontinuous microemulsions.

A theoretical investigation of the influence of the second critical micelle concentration on the solubilization capacity of surfactant micelles

“…k c is about kT and 2k c +k c equal to a few kT, as previously obtained for microemulsion droplets formed by non-ionic 30,33 as well as ionic surfactants. 34 This result is a strong evidence that the bending elasticity approach constitutes an accurate description of less curved large microemulsion droplets as well as of more highly curved micelles and small microemulsion droplets.…”

“…(8). 30 It is also possible to relate the planar interfacial tension and average radius with the effective bending constant k eff = κkT /4π (equivalent to κ) in accordance with…”

Entropic networks in colloidal, polymeric and amphiphilic systems

“…The observed, re-entrant phase separation, characterized by the closed loops, is explained as a direct result of the connected topology of the network that induces an effective attraction between junction points in the network. The topologically induced attraction, which is governed by the material-independent statistics of the junctions, explains the experimentally observed universality demonstrated by the data collapse of phase diagrams of non-ionic microemulsions [18,19].…”

Thermodynamics and Bending Energetics of Microemulsions

“…The three bending elasticity constants H 0 , k c and k c influence various properties of self-assembled surfactant monolayers and are expected to assume values that reflect the chemical properties of the constituent surfactant or surfactant mixture as well as environmental properties such as temperature and electrolyte concentration. They may be interpreted as thermodynamic parameters that may be determined from experiments [10][11][12][13] as well as calculated from a suitable molecular model [14][15][16] by means of minimizing the free energy per molecule of a surfactant interfacial layer at given values of H and K.…”