ABSTRACT: Water retention and transport in soils is dependent upon the surface tension of the aqueous phase. Surfactants present in
aqueous solution reduce the surface tension of aqueous phase. In soil–water systems, this can result in water drainage and
reductions in field capacity and hydraulic conductivity. In this investigation, the surface tension of surfactant solutions
mixed with soil—in a constant fixed ratio—was measured as a function of surfactant concentration. Two anionic surfactants
were used: sodium dodecyl sulphate and sodium bis (2-ethylhexyl) sulfosuccinate. Two soils were also used—a clay soil and
a sandy soil. The key observation made by this investigation was that the addition of soil to the surfactant solution provided
a further component of surface tension reduction. Neither soil sample reduced the surface tension of water when surfactant
was absent from the aqueous phase, though both soils released soil organic matter at low surfactant concentrations as shown
by measurement of the chemical oxygen demand of the supernatant solutions. Furthermore, both surfactants were shown to be
weakly adsorbed by soil as shown by the use of a methylene blue assay. It is therefore proposed that the additional reduction
in surface tension arises from synergistic interactions between the surfactants and dissolved soil organic matter.
KeywordsSurfactant-Soil water-Surface tension
Water Air and Soil Pollution 04/2012; 209(1):3-13. · 1.63 Impact Factor
ABSTRACT: 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.
Colloids and Surfaces A Physicochemical and Engineering Aspects 212(1):9-17. · 2.24 Impact Factor
ABSTRACT: 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.
Thermochimica Acta 417(2):201-206. · 1.80 Impact Factor