Solution behavior of a surfactant aldehyde–the oxidation product of an alcohol ethoxylate

It has previously been shown that alcohol ethoxylates readily undergo autoxidation and that one of the major oxidation products is the surfactant aldehyde, i.e. an ethoxylate carrying a –CH₂CHO group at the terminal end of the polyoxyethylene chain. In this work the cloud point, phase behavior and aggregation characteristics of the surfactant aldehyde produced by oxidation of C₁₂H₂₅(OCH₂CH₂)₅OH (C₁₂E₅) are determined and compared with the values obtained with the parent surfactant. It was found that the physico–chemical behavior of the two species was very similar, which indicates that a considerable portion of the aldehyde group is in hydrated state, i.e. the surfactant aldehyde consists of a mixture of aldehyde in carbonyl form and the corresponding geminal diol. The cloud point of the surfactant aldehyde decreased rapidly with time, even when it was stored at low temperature. Also the parent surfactant and its homologue C₁₂E₆ exhibited a decrease in cloud point during storage. For instance, a 1% aqueous solution of C₁₂E₆ showed a cloud point decrease from 62 to 32°C after 4 months storage at 40°C. Such a change in solution behavior can have important practical implications.