Membrane formation, liquid

In the classical set-up of bulk liquid membranes, the membrane phase is a well-mixed bulk phase instead of an immobilized phase within a pore or film. The principle comprises enantioselective extraction from the feed phase to the carrier phase, and subsequently the carrier releases the enantiomer into the receiving phase. As formation and dissociation of the chiral complex occur at different locations, suitable conditions for absorption and desorption can be established. In order to allow for effective mass transport between the different liquid phases involved, hollow fiber... 

The oscillation at a liquid liquid interface or a liquid membrane is the most popular oscillation system. Nakache and Dupeyrat [12 15] found the spontaneous oscillation of the potential difference between an aqueous solution, W, containing cetyltrimethylammo-nium chloride, CTA+CK, and nitrobenzene, NB, containing picric acid, H" Pic . They explained that the oscillation was caused by the difference between the rate of transfer of CTA controlled by the interfacial adsorption and that of Pic controlled by the diffusion, taking into consideration the dissociation of H Pic in NB. Yoshikawa and Matsubara [16] realized sustained oscillation of the potential difference and pH in a system similar to that of Nakache and Dupeyrat. They emphasized the change of the surface potential due to the formation and destruction of the monolayer of CTA" Pic at the interface. It is... 

Several manufacturers introduced products amenable for this solid-supported LLE and for supported liquid extraction (SLE). The most common support material is high-purity diatomaceous earth. Table 1.8 lists some commercial products and their suppliers. The most widely investigated membrane-based format is the supported liquid membrane (SLM) on a polymeric (usually polypropylene) porous hollow fiber. The tubular polypropylene fiber (short length, 5 to 10 cm) is dipped into an organic solvent such as nitrophenyl octylether or 1-octanol so that the liquid diffuses into the pores on the fiber wall. This liquid serves as the extraction solvent when the coated fiber is dipped... 

This chapter is concerned with processes that lead to formation of ISE membrane potentials. The membrane potentials of electrodes with liquid membranes containing a dissolved ion-exchanger ion or a dissolved ionophore (ion carrier), and of electrodes with solid or glassy membranes will be considered. More complicated systems, for example ISEs with a gas gap and enzyme electrodes, will be discussed in chapters 4 and 9. 

To obtain theoretical expressions for E corresponding to (1), additional restrictions must be incorporated, besides those given in the preceding list. Assuming cations Iz+ and Jz + to be of the same charge z+ and the formation of any or all l n (n = 1, 2,..., N, respectively, M) cation-carrier complexes possible, the expressions given in Table 11 are obtained.33 These are based on the assumption that the concentration [cs(x)] of the uncomplexed carrier S in the liquid membrane remains constant and that... 

The performance of calixarenes as cation carriers through H20-organic solvent H20 liquid membranes has also been studied.137 In basic metal hydroxide solutions, the monodeprotonated phenolate anions complex and transport the cations, while [18]crown-6 does not, under the same conditions. Low water solubility, neutral complex formation and potential coupling of cation transport to reverse proton flux have been cited as desirable transport features inherent in these molecules.137... 

Partitioning of components between two immiscible or partially miscible phases is the basis of classical solvent extraction widely used in numerous separations of industrial interest. Extraction is mostly realized in systems with dispergation of one phase into the second phase. Dispergation could be one origin of problems in many systems of interest, like entrainment of organic solvent into aqueous raffinate, formation of stable, difficult-to-separate emulsions, and so on. To solve these problems new ways of contacting of liquids have been developed. An idea to perform separations in three-phase systems with a liquid membrane is relatively new. The first papers on supported liquid membranes (SLM) appeared in 1967 [1, 2] and the first patent on emulsion liquid membrane was issued in 1968 [3], If two miscible fluids are separated by a liquid, which is immiscible with them, but enables a mass transport between the fluids, a liquid membrane (LM) is formed. A liquid membrane enables transport of components between two fluids at different rates and in this way to perform separation. When all three phases are liquid this process is called pertraction (PT). In most processes with liquids membrane contact of phases is realized without dispergation of phases. 

Wang, Y.C. and Doyle, F.M. (1999) Formation of epoxy skin layers on the surface of supported liquid membranes containing polyamines. Journal of Membrane Science, 159, 167. 

Neplenbroek, A.M., Bargeman, D. and Smolders, C.A. (1992) Mechanism of supported liquid membrane degradation - emulsion formation. Journal of Membrane Science, 67, 133. 

Ultrasound-assisted emulsification in aqueous samples is the basis for the so-called liquid membrane process (LMP). This has been used mostly for the concentration and separation of metallic elements or other species such as weak acids and bases, hydrocarbons, gas mixtures and biologically important compounds such as amino acids [61-64]. LMP has aroused much interest as an alternative to conventional LLE. An LMP involves the previous preparation of the emulsion and its addition to the aqueous liquid sample. In this way, the continuous phase acts as a membrane between both the aqueous phases viz. those constituting the droplets and the sample). The separation principle is the diffusion of the target analytes from the sample to the droplets of the dispersed phase through the continuous phase. In comparison to conventional LLE, the emulsion-based method always affords easier, faster extraction and separation of the extract — which is sometimes mandatory in order to remove interferences from the organic solvents prior to detection. The formation and destruction of o/w or w/o emulsions by sonication have proved an effective method for extracting target species. 

A few proteins exist that sequester PIP2 in a cholesterol-dependent manner. One of these proteins is the N-terminal myristoylated peptide of NAP-22 (33, 34). Combined confocal microscopy and AFM show that this peptide forms new cholesterol-rich domains within the liquid-disordered domain to which it attracts PIP2 (31). In addition, a peptide segment of caveolin promotes the formation of membrane domains containing both cholesterol and PIP2 (35). 

An emulsion liquid membrane (ELM) system has been studied for the selective separation of metals. This system is a multiple phase emulsion, water-in-oil-in-water (W/O/W) emulsion. In this system, the metal ions in the external water are moved into the internal water phase, as shown in Fig. 3.4. The property of the ELM system is useful to prepare size-controlled aiKl morphology controlled fine particles such as metals, carbonates/ and oxalates.Rare earth oxalate particles have been prepared using this system, consisting of Span83 (sorbitan sesquioleate) as a surfactant and EHPNA (2-ethyl-hexylphospholic acid mono-2-ethylhexyl ester) as an extractant. In the case of cerium, well-defined and spherical oxalate particles, 20 - 60 nm in size, are obtained. The control of the particle size is feasible by the control of the feed rare earth metal concentration and the size of the internal droplets. Formation of ceria particles are attained by calcination of the oxalate particles at 1073 K, though it brings about some construction of the particles probably caused by carbon dioxide elimination. 

Internal Phase Composition As with the continuous phase, the internal phase properties also influence the properties of the ELM. Ionic strength, pH, and the presence of organic species will impact on the stability of the ELM. Emulsion liquid membranes work on the basis that the polar substances (usually high concentrations of acid or base) contained in the internal phase are impermeable to the membrane phase. However, the presence of the surfactant can cause the uptake of these compounds by the formation of reverse micelles [97]. 

Supported liquid membranes, consisting of an organic solution of -octyl(phenyl)-A,iV-diisobutylcarbamoylmethylpho-sphine oxide (CMPO) and tributyl-phosphate (TBP) in decalin, were capable of selective separation and concentration of actinide and lanthanide ions from aqueous nitrate feed solutions and from synthetic nuclear wastes where the strip solution is a mixture of formic acid (FA) and hydroxylammonium formate (HAF) [106,107]. TBP is added to CMPO to improve its solubility in aliphatic diluents. Although low concentration of nitric acid was initially used as the strippant solution, a gradual... 

Liquid Membranes Emulsion liquid-membrane (ELM) extraction involves intentional formation of an emulsion between two immiscible liquid phases followed by suspension of the emulsion in a third liquid that forms an outer continuous phase. The encapsulated liquid and the continuous phase are miscible. The liquid-membrane phase is immiscible with the other phases and normally must be stabi-... 

The calcium ion liquid-membrane electrode is a valuable tool for physiological investigations because this ion plays important roles in such processes as nerve conduction, bone formation, muscle contraction, cardiac expansion and contraction, renal tubular function, and perhaps hypertension. Most of these processes are influenced more by the activity than the concentration of the calcium ion activity, of course, is the parameter measured by the membrane electrode. Thus, the calcium ion electrode (and the potassium ion electrode and others) is an important tool in studying physiological processes. 

Y. Wang, Y. S. Thio, and F. M. Doyle, Formation of Semi-permeable Polyamide Skin Layers on the Surface of Supported Liquid Membranes, J. Membr. Sci., 147, 109-116 (1998). 

Liquid membranes with an ionophore L function via complex formation between the ionophore and an ion in the aqueous phase. When this ion is a monovalent cation M" " the membrane phase contains the cation in the form ML" ", that is, completely complexed with the ionophore. The other components of the membrane are a hydrophobic solvent S which constitutes the majority of the liquid phase and a hydrophobic anion A. The concentration of free cation M within the membrane is very small but must be considered in assessing the Donnan equilibria on each side. The description of the membrane system is... 

---