Permeability Solvent dependence

Table 9-10 Solvent dependence of the relative permeability and solubility exemplified with heptanol in LDPE at 23 °C.

In facilitated transport of metal ions through LM, the metal ions are transported through the membrane against their own concentration gradient, termed as the uphill transport. The driving force in such processes is provided by the chemical potential difference of the species other than the diffusing ones on either side of the membrane. The permeability of the transported species is decided by the parameters such as membrane thickness, pore structure, aqueous diffusion coefficient of the species, aqueous diffusion layer thickness, and distribution and diffusion coefficients of the transported species in the LM phase. The diffusion of the species in the carrier solvent depends on the membrane characteristics (viz., porosity and tortuosity) and viscosity of the solvent, while the aqueous diffusion of the metal ions depends upon the flow rate and diffusivity of metal species in the aqueous phase. On the other hand, the overall transport rates of the species can be controlled through various parameters such as feed composition, carrier concentration, and receiver phase composition. 

D is the collective diffusion coefficient of the fluorinated ion exchange polymer, which is given by the effective solvent permeability coefficient and the meehanieal constant of the polymer network. The effective solvent permeability coefficient depends on the ratio of the... 

Only freeze-drying, or changing the liquid phase for a solvent with low surface tension before drying, allows air-dried samples without pit aspiration to be obtained (Comstock and Cote, 1968 Meyer, 1971 Bolton and Petty, 1978 Fumoto et ak, 1984). The permeability values depend on the species and on the author, but all these data show that air-dried samples, with aspirated pits, have permeability values considerably smaller than unaspirated samples (typically ranging from 1 to 10%). Due to thicker cell walls, smaller pit radii, and more rigid structures, the percentage of aspirated pits is much less in the latewood part of samples (Siau, 1984). 

A plot of A versus r, the calibration curve of OTHdC, is shown in Fig. 22.2. The value of constant C depends on whether the solvent/polymer is free draining (totally permeable), a solid sphere (totally nonpermeable), or in between. In the free-draining model by DiMarzio and Guttman (DG model) (3,4), C has a value of approximately 2.7, whereas in the impermeable hard sphere model by Brenner and Gaydos (BG model) (8), its value is approximately 4.89. 

Recovery of DNAPL is a very slow process that is alfected by those factors encountered with LNAPL (i.e., relative permeability, viscosity, residual hydrocarbon pool distribution, site-specific factors, etc ). Dissolution of a DNAPL pool is dependent upon the vertical dispersivity, groundwater velocity, solubility, and pool dimension. Dispersivities for chamolid solvent are estimated for a medium to coarse sand under laboratory conditions on the order of 1(L3 to 1(H m. Thus, limited dispersion at typical groundwater velocities is anticipated to be slow and may take up to decades... 

In contrast to the 02 generator, the polymer used in the O2 sensor must be highly gas permeable but solvent impenetrable. Solvent penetration will alter the probe properties and make calibration dependent on environment. Furthermore, good solvents for the probe will leach the probe and destroy the sensor. Again, it is important that the support dissolve the probe well and not greatly quench the luminescence. 

Moreover, the unique adsorption properties of GEC allowed the very sensitive electrochemical detection of DNA based on its intrinsic oxidation signal that was shown to be strongly dependent of the multi-site attachment of DNA and the proximity of G residues to GEC [100]. The thick layer of DNA adsorbed on GEC was more accessible for hybridization than those in nylon membranes obtained with genosensors based on nylon/GEC with a changeable membrane [99,101,102]. Allhough GEC has a rough surface, it is impermeable, while nylon is more porous and permeable. DNA assays made on an impermeable support are less complex from a theoretical standpoint [7] the kinetics of the interactions are not compUcated by the diffusion of solvent and solutes into and out of pores or by multiple interactions that can occur once the DNA has entered a pore. This explained the lower hybridization time, the low nonspecific adsorplion and the low quantity of DNA adsorbed onto GEC compared to nylon membranes. 

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