Dielectric liquid membranes

A chemical destruction method that has been used for the treatment of PCBs in contaminated dielectric liquids or soil is based on the reaction of a polyethylene glycol/potassium hydroxide mixture with PCBs (De Filippis et al. 1997). This method can be used successfully for the destruction of higher chlorinated PCBs with an efficiency of >99%, but was found to be unsuitable for the treatment of di- and trichlorobiphenyls due to low destruction efficiencies (Sabata et al. 1993). Irradiation of PCBs in isooctane and transformer oil by y-radiation resulted in degradation of PCBs to less chlorinated PCBs and PCB-solvent adducts (Arbon et al. 1996). Supercritical fluid technology has shown promise as a method for extraction of PCBs from soils, coupled with supercritical water oxidation of the extracted PCBs (Tavlarides 1993,1998a). Hofelt and Shea (1997) demonstrated the use of semipermeable membrane devices to accumulate PCBs from New Bedford Harbor, Massachusetts water. Another method showing... 

More particularly, Fig. 21 shows the selectivity lines of membranes consisting of an anion exchanger and different diluents. As the dielectric constant of the diluent rises, the selectivity coefficient drops. The same trend is seen in Fig. 22. This phenomenon may well be an expression of the model of Eisenmann [20], in which he showed that the potential of a liquid membrane is composed of two factors ... 

Semiconductor processing technologies have often been used to produce ISEs, particularly as field-effect transistors (FETs) with ion-selective layers like silicon oxide over the gate region. Such ion-selective FETs (ISFETs) are, in principle, solid ISEs, although sometimes the dielectric over the gate is covered with a second, liquid membrane-type layer to achieve different selectivities. 

A large number of neutral ionopohores for cations and anions have been synthesized and many are commercially available (Morf and Simon, 1978). The organic solvent forming the gel membrane is hydrophobic and has a high dielectric constant. Examples of membrane constituents of liquid ISEs are given in Table 6.4. 

The variation of the defined dissociation constant, obtained on the basis of this dielectric model, is plotted in Fig. 1.6. The reaction Eq. (1.3) in liquid water becomes unfavorable from the perspective of the free energy upon exceeding 500 K on the saturation curve, where the liquid density falls below about 85% of the triple-point density. Nevertheless, this sulfonic acid head group would still be considered a strong acid in bulk aqueous solution at these elevated temperature and reduced-density conditions. These results give perspective for the view that insufficient hydration can result in incomplete dissociation of sulfonic acid species in membranes. 

A Novocontrol Alpha-Analyzer (v=10 -10 Hz) was used for dielectric measurements, both at atmospheric and at high pressure. For atmospheric pressure measurements, a parallel plate capacitor separated by a quartz spacer (empty capacitance 90 pF) and filled by the sample was placed in the nitrogen flow Quattro cryostat (T= 100-3 60 K). For high pressure measurements, a sample-holder multi-layer capacitor (empty capacitance 30pF) was separated from the pressurizing fluid (silicon oil) by a Teflon membrane. The high pressure chamber (Cu-Be alloy), provided by UNIPRESS, was connected to a hydraulic pump able to reach 700 MPa, and controlled in the interval 195-360 K within 0.1 K by means of a thermally conditioned liquid flow. 

Potential applications of liquid crystalline templated polymer gels range from separation media (membranes, chromatography columns, or electrophoresis gels) to low dielectric constant insulators for microelectronic devices, to nano-structured optoelectronic devices, to catalysts supports, drug carriers, or materials for controlled release. 

Figure 1 depicts the electric displacement eE [where E is the field and e the dielectric constant] across the vesicle membrane of thickness 6 on the assumption that the media of both sides have equal ionic strengths. The resting potential difference across the membrane, is of the liquid-junction type but is usually close to a Nernst potential. The Debye lengths in both the ionic media are X. Inside the membrane E = / the constant Planck field. Outside the membrane, the field is assumed to decline in accord with a linear Goiiy-Chapman model, E = Epe, so that Fy = + 2A). If we define... 

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