The removal of dense nonaqueous phase liquid mixtures (DNAPLs) from rocks and subsurface soils is an ongoing remedial challenge. Very often the wetting preferences of the system are not altered by exposure to the DNAPL. However, there are systems where the wetting properties of the solid phase have been altered from strongly water wetting by exposure to the DNAPL. In these cases some technique is necessary for reducing the work of adhesion between the DNAPL and the mineral surface. The focus of this report is the problems posed by coal tar in unconsolidated sands. It is shown that coal tar can alter the wetting properties of quartz, the principal component of sands, and is thus capable of adhering to the surface. In this investigation the ability of several members of the poloxamine family of polymeric surfactants to aid in the removal of coal tar from sand was evaluated. The poloxamines are tetrafunctional block copolymeric surfactants, which contain four poly(ethylene oxide)-block-poly(propylene oxide) chains joined to a central ethylenediamine moiety via the nitrogen atoms. Contact angle measurements of coal tar on a quartz surface immersed in aqueous surfactant solution and the interfacial tension between coal tar and aqueous surfactant solution have been measured. Coal tar/water interfacial tensions are reduced to values in the region of 2 mN m-1 at surfactant concentrations of approximately 0.1 w/v %. Poloxamine surfactant impact on the static contact angle is more complex. In some cases the polymeric surfactants alter the wetting behavior from strongly water wetting to weakly water wetting. However, other poloxamines appear to have little if any impact on the contact angle, which remains strongly water wetting. The foregoing measurements have then been used to calculate the work of adhesion of the coal tar to quartz and the results qualitatively compared with the concentration of surfactant solution required to visually demonstrate the complete de-adhesion of coal tar to the quartz. It is shown that at surfactant concentrations below the critical micelle concentration (cmc) of the surfactant, the work of adhesion can be reduced sufficiently to ensure complete removal of coal tar from both quartz and sand.

The solubilisation of exemplar polyaromatic hydrocarbons (PAHs) in aqueous solutions of the block co-polymeric surfactant T803 has been investigated. The PAHs used were naphthalene, phenanthrene and pyrene. T803 is a tetrafunctional block co-polymer derived by way of the coupling of ethylene oxide and propylene oxide to ethylene diamine. The presence of the ethylene diamine moiety provides the compound with pH functionality. In particular, micellisation in these systems is shown to be pH dependent. As a consequence, solubilisation in T803 solutions is also shown herein to be pH dependent, giving rise to considerable changes in the apparent aqueous solubilities of the PAHs. A switch in pH from 4 to 10.3 changes the apparent aqueous solubility of naphthalene, phenanthrene and pyrene by one, two and three orders of magnitude, respectively. Likewise, changes in temperature from 25 to 40 ◦C also produce changes of similar orders of magnitude in the apparent aqueous solubilities of phenanthrene and pyrene at a pH of 5.6 and T803 concentration of 5 mM.

Differential scanning calorimetry has been used to investigate the effect of pH upon the temperature interval over which aggregation occurs in aqueous solutions of the ethylene oxide (EO)/propylene oxide (PO) block co-polymeric compound tetronic T701 (molecular formula EO4PO13)2NCH2CH2N(PO13EO4)2). Self association, in this system, occurs at elevated temperatures because the PO blocks become increasingly non-polar and, as a consequence, self associate because of the hydrophobic effect. pH titration shows that the central ethylene diamine moiety is di-basic with pKa values of 3.8 and 8. Thus, in aqueous solution when the pH value is below 8 a necessary pre-condition for self association is deprotonation. A theoretical model is developed-based upon this hypothesis-which attempts to replicate, with some success, the effect of pH upon the calorimetrically observed T701 self association process.

Poloxamines are tetra functional block copolymers, which contain four polyethylene oxide (PEO)-polypropylene oxide (PPO) chains joined to a central ethylene diamine moiety by way of the nitrogen atoms. Surface and interfacial tensions at the air-water and hexane-water interfaces have been determined over a wide concentration range for several of these block copolymeric amphiphiles. Titration data indicates that these molecules are dibasic. Two pKa values-corresponding to proton loss from the central nitrogen atoms of the molecule-have been determined by fitting titrimetric data to a thermodynamic model of the titration process. The values obtained are fairly constant for different poloxamines, which suggests that varying the block size has little impact upon these pKa values. However, the values obtained are lower than those observed for ethylene diamine and indicate that the attachment of the PEO-PPO chains to the nitrogen atoms does reduce their basicity. The Gibbs adsorption isotherm at the air-water interface is similar to the adsorption pattern reported for the poloxamers-linear PEO-PPO-PEO block copolymers [Langmuir 10 (1994) 2604] and shows that the highly branched poloxamines have similar interfacial properties as the poloxamers. Data is also reported on adsorption of poloxamines at the hexane-water interface. In the main it is concluded that those block copolymers with high PPO to PEO ratios and which are, therefore, relatively hydrophobic are more effective in reducing surface and interfacial tensions. These effects are, however, attenuated by changes in aqueous phase pH, which alters the charged nature of the poloxamine molecule.