Altering the spreading coefficient of coal tar systems using ethylene oxide-propylene oxide block copolymers

The impact of poloxamine copolymeric surfactants upon the spreading coefficient of coal tar in a three phase system comprising water, coal tar and air has been investigated. The poloxamines are branched ethylene oxide (EO) propylene oxide (PO) block copolymers which are frequently used in pharmaceutical formulations. They have low mammalian toxicities and may therefore prove useful in surfactant enhanced aquifer remediation schemes where there is regulatory concern over the use of surfactants in groundwater. The purpose of this study was to investigate the conditions under which spreading coal tar films are converted into entrapped lenses. To that end, measurements were made of the surface tension of a range of aqueous poloxamine solutions using the du Nöuy ring technique and coal tar aqueous phase interfacial tensions using drop shape analysis. The poloxamines demonstrated surface activity by reducing the surface tension of water and the coal tar/water interfacial tension. However, there were differences in the extent to which the various poloxamines reduced the interfacial and surface tensions, which was clearly related to their molecular composition. In particular, the most effective compounds were those with high PO:EO ratios. All the poloxamines investigated altered spreading conditions. It was demonstrated, however, that those poloxamines having a relatively high PO mass and a high PO:EO compositional ratio were the most effective in altering the spreading conditions from spreading to non-spreading.