Effect of polyoxyethylene chain length upon mixed surfactant solutions and temperature dependence on the surface tension

• Published in: Journal of colloid and interface science Vol. 78; no. 1; pp. 207 - 211
• Main Authors: Takasawa, Yosuke, Ueno, Minoru, Meguro, Kenjiro
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.11.1980
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(80)90509-3

The surface tensions of a series of polyethylene glycol- n-dodecyl ethers ( nED) were measured by the Wilhelmy plate method in the presence of constant 6.3 m M sodium dodecyl sulfate (SDS) at temperature of 15, 25, and 40°C, respectively. The surface tension curves for the mixed system of SDS and nonionic surfactants showed a flat portion in the range of which the mixed micelles in the solution and the two-dimensional ones on the water surface occur, respectively. The width of this flat portion decreased with shortening of the polyoxyethylene chain length, and when the unit of ethylene oxide in the chain reached 3ED, the flat portion disappeared. This limiting length in the ethylene oxide chain required for the disappearance of the flat portion, that is, the so-called critical length of the ethylene oxide chain, can be considered to be one of the critical values for the existence of mixed micelles and below the critical value only excess micelles of the nonionic surfactant exist in all ranges of the mixed concentration of the SDS and nonionic surfactants. Furthermore, the effects of temperature on the flat portion were investigated on the assumption that the rise in temperature rendered a similar effect with respect to the length of the flat portion to that of reducing the length of the polyoxyethylene chain.