Thesis Details

Thesis Title: Surface tension variations of solutions of surface-active agents with time
Thesis Author: Laurence T. Cleary
Abstract: Surface tension variations of solutions of Nacconol NRSF, Aerosol OT, Triton N-100, and sodium oleate were observed at 30 C using a modified capillarimeter. In the very dilute and very concentrated regions, rapid orientation and rearrangement occurred at the surface, and equilibrium was quickly attained. As a result, the solutions were stable, and the readings were reproducible. In the unstable region (0.01 percent), variations occurrred as the surface aged; the solutions behaved in a manner peculiar to the particular agent, and the results were not predictable. The agreement shown in the surface tension measurements using the oscillating drop and detaching ring as well as the capillary rise method was good for most of the dilute solutions (0.001 to 0.0001 percent), poor for the 0.01 percent solutions, and excellent for the concentrated solutons (0.2 percent). In nearly all the measurements, the oscillating drop values were higher than the corresponding capillary rise results, and considerably higher than the detaching ring values. The differences exhibited by the three methods were attributed to the time the surface had aged before the surface tension was determined. The surface tension of solutions of surface-active agents was a function of the material, the concentration, and the age of the surface. Since changes of the surface tension occurred only in solutions of ionic surface-active agents, it was concluded that surface tension variations on aging were connected with electrolytic dissociations. The nature of the change is determined by the relative rate of adsorption of solute ions into the surface, and the desorption of ions into the bulk of the solution through the formation of micelles.