Selective dissolution permeable membranes

Permeable Membranes as Applied to Selective Dissolution.—In most of the leaching and dissolution processes the material is shredded or ground so as to... 

Ion-selective membranes attain their permselectivity from ion-exchange, dissolution, or complexation phenomena. Different types of membranes are available for the construction of ion-selective electrodes glass and other solid state rods (crystals), liquid or polymer ion ecchangers, or dissolved ionophores. Many electrodes are commercially available with selec-tivities for different ions, mainly H, alkali metal cations, heavy metal ions, and halides or pseudohalides. Also gas-sensing electrodes may be constructed from an ion-selective electrode and a gas-permeable membrane [182]. Ion selective electrodes and gas-selective electrodes... 

CRITICAL ASSESSMENT OF THE METHOD VolSurf descriptors are able to predict absorption for a diverse set of drugs. The presented model is derived using a consistent frame of relevant chemically interpretable descriptors, which find applications in different local and general models. However, absorption is not only controlled by passive membrane permeability. There are other factors influencing in vivo human absorption namely the in vivo dissolution rate in small intestinal fluid and the dose used for the human study. Furthermore, active transport or efflux mechanisms are difficult to rule out but can only be partially monitored by in vitro experiments. These important pieces of information should be known before any QSAR analysis is attempted on human absorption. This lack of consistent information throughout the literature is difficult to overcome, in particular for human studies. Hence, this study for the dataset from Zhao et al. (2001) provides a reasonable attempt to address these problems to carefully selecting members of the final dataset. 

Multilayers may also be used for their permeation properties. Accordingly, membranes covered by multilayers have been employed for gas permeability measurements and for pervaporation studies [88,181,185,333-335]. These measurements showed, for example, 02/H20,C02/02, or toluene/ heptane selectivity. The permeation properties of polyelectrolyte multilayers are also important when they are used for the encapsulation of enzymes [210] or living cells [336,337]. The deposition of polyelectrolyte multilayers or of hybrid polyelectrolyte/inorganic multilayers on latex particles, and the subsequent dissolution or calcination of the latex beads leads to the fabrication of hollow spheres [94-96,338-340]. Potential applications of such hollow spheres are numerous, for example, for the controlled release and targeting of drugs. 

Unmodified ( native ), polymeric membranes often show strong plasticization effects when exposed to high partial pressures of C02, hydrocarbons, or ethylene oxide. Plasticization increases the inter-molecular distance and molecular motion of the polymer chains due to a decrease in inter- and/or intramolecular attractive forces. Consequently, the permeability for all feed components increases, whereas the selectivity decreases. Strong plasticization can even lead to a partial dissolution of the membrane. Hydrocarbons present in natural gas can reduce the selectivity by 30-50% due to plasticization. Plasticization can be limited by cross-linking the polymer chains through either covalent or ionic bonds (Figure 2) but will not be detailed here further (see Ref. 36 instead). - ... 

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