Shape Similarities of Ultra‐Low Interfacial Tension Curves in Ternary Microemulsion Systems of the Water‐Alkane‐CiEj Type

Abstract

AbstractThe interfacial tensions between water‐ and oil‐rich phases in microemulsion systems have been measured for a series of ternary water‐alkane‐CiEj systems. It is found that interfacial tensions vary over orders of magnitude with temperature displaying a pronounced minimum for each surfactant. The center of the three‐phase temperature interval, Tu‐T1, i.e. the phase inversion temperature (PIT), corresponds to the temperature Tm of the minimum in interfacial tension. Increasing the surfactant chain length the minimum value decreases by 3 orders of magnitude for a change of i from 6 to 12. Interestingly, all interfacial tension curves have a similar shape. Centering the curves around Tm and reducing the temperature scale by Tu‐T1 permits determining the factors, by which the individual interfacial tension curves differ. The factors are found to be proportional, respectively, to square of the maximum length scale ζ or the inverse surfactant volume fraction Φc,i in the interface. Accordingly, plotting σab/Φc, j2 vs. 2(T‐Tm)/(Tu‐T1) an almost perfect superposition of all interfacial tension curves is observed.