Influence of Crown Ethers on the Electric Percolation of AOT/Isooctane/Water (w/o) Microemulsions

Abstract

A study was carried out on the influence of different crown ethers on the electric percolation of AOT/isooctane/water microemulsions. The crown ethers used were chosen on the basis of two fundamental criteria: (a) the different sizes of the molecules, where variation is found in the external size as well as the size of the cavity, and (b) the different solubilities of the ethers in water. In all cases we observed a dual behavior of the crown ethers with regard to the percolative phenomenon. At low additive concentrations we observed how the presence of the crown ethers caused an increase in the percolation temperature of the microemulsions, whereas at high additive concentrations there was a reduction in the percolation temperature causing the percolation threshold of the system to move forward. This dual behavior allowed us to define the compensation concentration, which corresponds with the crown ether concentration at which there is no effect on the percolative phenomenon. We observed a correlation between the effect exerted by the crown ethers and the size of the cavity. This shows the importance of the capacity to complexate Na+ and solubilize it in the interface and the continuous medium on the electric percolation. We also observed a correlation between the effect of the crown ethers on the percolation temperature and their external size. This shows the importance of their inclusion in the interface on the percolative phenomenon. Such an inclusion modifies the properties of the AOT film, facilitating the exchange of matter between droplets. We also obtained a satisfactory multiparametric correlation between the logarithm of the compensation concentration, the logarithm of the distribution parameter of the crown ether between water and 1-octanol, and the number of oxygen atoms in the crown ether. This correlation shows that the effect of the crown ethers on the electric percolation is due to its size and capacity to sequester ions, as well as to its solubility in the interface of the microemulsion.

Influence of glymes upon percolative phenomena in AOT-based microemulsions

“…1). This behavior is significantly different from that observed with crown ethers, where we had observed [5] an increase in the percolation temperature of the system as the crown ether concentration increased, until a maximum value was reached, from which the percolation temperature decreased. The effect exerted by glymes is similar to that of other small organic molecules [8], which is considered as a consequence of two different effects: (a) the inclusion into the surfactant film and (b) the replacement of water molecules from the interface.…”

“…The composition of the microemulsions remained constant and The conductivity was measured using a Crison GPL 32 conductivimeter. Details about the experimental procedure are described elsewhere [5].…”

“…The influence of crown ethers on the percolation temperature has been studied [2][3][4][5]. The observed behavior at low additive concentrations is an increase in the percolation temperature of the microemulsions, whereas at high concentrations there is a reduction in the percolation threshold.…”

Physicochemical studies on microemulsions

“…This can be achieved in two ways: either by adding water to a constant mole ratio of amphiphile (ionic surfactant + cosurfactant) and oil (normally linear aliphatic hydrocarbon oil) or by increasing temperature at "volume percolation" and the second is called "temperature percolation." The said phenomenon of conductance percolation has been amply studied [4][5][6][7][8][9][10][11][12][13][14][15][16][17] with Aerosol-OT (AOT) as the surfactant with hydrocarbon oils for the amphiphile does not require a cosurfactant (normally lower alkanols and amines) for microemulsification, and relatively simple to interpret. Other ionic surfactants need nonionic surfactants and cosurfactants in combination to augment the process [18a,18b].…”

Influence of Amphiphiles on Percolation of AOT-Based Microemulsions Prediction Using Artificial Neural Networks

“…In the last decade, our research group has studied the effects of different additives on the electrical conductivity, and other properties, for water/AOT/isooctane microemulsions (aerosol OT or dioctyl sodium sulfosuccinate, isooctane and water) [5,[15][16][17][18][19][20][21][22]. The influence of different additives was explained on the basis of changes in the surfactant film structure and different solubility of the complex system.…”