Influence of Crown Ethers and Macrocyclic Kryptands upon the Percolation Phenomena in AOT/Isooctane/H₂O Microemulsions

Abstract

The influence of several additives upon the properties of the system AOT/isooctane/water has been investigated. The presence of crown ethers (18-crown-6) and kryptand complexes (kryptand 222, kryptand 221 and kryptand 211) have an important effect upon the electrical percolation phenomena. Low macrocyclic concentrations hinder the electrical percolation phenomenon. This effect seems to be due to the ability of macrocycles to complex ions and transfer them to the interface. Medium and high macrocyclic concentrations favor the electrical percolation, and this effect is related to their interfacial association to the AOT head groups. The observed behavior has been explained in terms of critical packing parameter, and it is compared with the influence of small additives as electrolytes or small organic molecules.

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].…”

“…Other ionic surfactants need nonionic surfactants and cosurfactants in combination to augment the process [18a,18b]. A literature survey reveals that temperature-induced percolation [4][5][6][7][8][9][10][11][12][13][14][15][16][17] has been studied more frequently than volumeinduced percolation [5,[17][18][19][20][21][22][23][24] using all kinds of aliphatic hydrocarbon oils. The studies with nonaliphatic hydrocarbon oils [25,26] are much lower in number.…”

“…The studies with nonaliphatic hydrocarbon oils [25,26] are much lower in number. The effect of additives on the said percolation process has also been elaborately studied in recent years [8][9][10][11][12][13][14].…”

Microemulsions: Thermodynamic and Dynamic Properties

“…Similar behavior is observed with variation in water content, temperature or volume fraction for the fixed composition of the microemulsion. This phenomenon is known as electric percolation, (Hamilton et al, 1990, Garcia-Rio et al, 1997, Hait et al, 2001, Borkovec et al, 1988, Papadimitriou et al, 1993, Mehta et al, 1995, 1998, 1999, 2002) the moment at which an abrupt transition occurs from poor electric conductor, system (`10 -7 Ω -1 cm -1 ) to the system with fluid electric circulation (10 -3 Ω -1 cm -1 ). As a consequence of ion transfer it yields a sigmoidal σ −θ and σ −φ profile.…”

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.…”