Surface tension and cloud point changes of polyoxyethylenic non-ionic surfactants during autoxidation

Abstract

Changes in the surface tension-concentration curves of the non-ionic surfactant cetomacrogol, a polyoxyethylenic (POE) hexadecyl ether containing about 24 ethylene oxide (EO) groups, have been examined during autoxidation of aqueous solutions. The curves exhibit decreases in cmc values and changes in the slopes below and above the cmc which lead to the loss of the sharp break characteristic of micelle-formation. There is also a progressive decrease in the cloud point during autoxidation. Surface tensions and cloud points of a series of known POE hexadecyl ethers containing from 10 to 60 EO units have been measured and related to the number of EO units present. From these data, it is apparent that autoxidation of cetomacrogol is accompanied by degradation of the POE chain rather than the hydrocarbon chain, the number of EO units lost up to the time at which the solution becomes turbid being about 14. The significance of such measurements is discussed in relation to the detection of decomposition and pending rapid decomposition in synthesized and commercial surfactants.