Changes in interfacial tension of chlorinated solvents following flow through U.K. soils and shallow aquifer material

The interfacial tension (IFT) that arises at the interface between water and an immiscible organic liquid is a key parameter affecting the transport and subsequent fate of the organic liquid in water-saturated porous media. In this paper, data are presented that show how contact between a range of soil types and chlorinated hydrocarbon solvent (CHS) dense nonaqueous phase liquids (DNAPLs) can affect DNAPL/water IFT values. The soils examined are indicative of U.K. soil types and shallow aquifer materials. The solvents investigated were tetrachloroethylene (PCE) and trichloroethylene (TCE). Lab grade, recovered field DNAPL and industrial waste chlorinated solvent mixtures were used. The data from batch and column experiments invariably revealed that water/DNAPL IFT values change following contact with unsaturated soils. In the majority of cases, the IFT values increase following soil exposure. However, after contact with an organic-rich soil, the IFT of the lab grade solvents decreased. The experimental evidence suggests that these reductions are linked to the removal of organic material from the soil and its subsequent incorporation into the solvent IFT increases in the case of lab solvents are shown to be linked to the removal of stabilizers (added by the manufacturers to obviate degradation) that are removed by adsorption to soil mineral surfaces. Similarly, it is conjectured that adsorption of surface-active compounds from the industrial waste samples to soil surfaces is responsible for increases in the IFT in these samples. Finally, it was observed that invading CHSs are capable of dissolving and subsequently mobilizing in-situ soil contaminants. GC/MS analysis revealed these mobilized soil contaminants to be polyaromatic hydrocarbons and phthalate esters.     

High vibrational temperatures in optically-pumped CO2

A pulsed 4.3-μm CO₂ laser was used to optically pump mixtures of CO₂ and He, and create transient gain at 9 and 10 μm. A conventional continuous-wave CO₂ laser operating on both regular and sequence bands measures this transient gain, and determined the ν₃ (asymmetric stretching)-mode vibrational temperature T₃. The measured values of T ₃ are generally much higher than those attained in discharge-excited CO₂. It is shown that a Treanor distribution must be used to describe the populations in the ν₃ -mode when dilute mixtures of CO₂ in He are optically pumped to ν₃-mode temperatures of 3000 to 4000 K. Under these conditions the sequence-band gain coefficients are almost equal to those on the regular bands. The collisional relaxation of energy from the ν₃ mode shows evidence of fast V-T relaxation at high values of T₃, followed by a slower relaxation rate characteristic of the 00⁰1 population lifetime