Solubility-selective membrane

Reijerkerk, S. R., Nijmeijer, K., Ribeiro, C. P., Jr., Freeman, B. D., Wessling, M. (2011). On the effects of plasticization in C02/Ught gas separation using polymeric solubility selective membranes. Journal of Membrane Science, 367, 33—44. 

Solubility-Selective Membrane The solubility coefficient reflects how many gas molecules can be sorbed in polymer membranes. It depends on the condensability as well as the physical interactions of the penetrants with the polymer membrane. Solubility is determined by the concentration of the sorbed gas per unit polymer volume. Generally, the concentration as a function of pressure at constant temperature shows a sorption isotherm with a characteristic shape that is concave to the pressure axis. The solubihty-selectivity term in Eq. (24.3) is thermodynamic in nature and is governed by the relative polymer-penetrant interactions and the relative condensabihty of the penetrants. Solubility-selectivity terms contribute significantly to separations of condensable vapors and polar molecules. 

Ion-selective membranes derive their permselective properties from either ion exchange, solubility or complexation phenomena. Current ion-selective electrodes contain membranes which consist of glass, solid or liquid phases. 

Approaches to make a polymeric membrane selective to C02 attempt to enhance the solubility selectivity of the polymer material for C02 and reduce the diffusivity selectivity of the polymer that favors smaller hydrogen molecule. The permeability of a polymer membrane for species A, PA, is often expressed as (Ghosal and Freeman, 1994)... 

It follows from Equation 8.13 that aA/B can be expressed as the product of the diffusivity selectivity, DA/DB, and the solubility selectivity, SA/SB. Diffusion (or mobility) selectivity is governed primarily by the size difference between gas molecules and always favors smaller gas molecules. Solubility selectivity is controlled by the relative condensability of the gases in the polymer and their relative affinity for the polymer. Solubility selectivity typically favors larger, more condensable molecules. From Equation 8.13, it is seen that the product of gas mobility and solubility selectivity determines the overall membrane selectivity. It is clear that for a membrane to be C02 selective, it must have high diffusivity selectivity based on the affinity for C02 but it should be flexible enough to permeate larger molecules such... 

The next three chapters (Chapters 9-11) focus on the deposition of nano-structured or microstructured films and entities. Porous oxide thin films are, for example, of great interest due to potential application of these films as low-K dielectrics and in sensors, selective membranes, and photovoltaic applications. One of the key challenges in this area is the problem of controlling, ordering, and combining pore structure over different length scales. Chapter 9 provides an introduction and discussion of evaporation-induced self-assembly (EISA), a method that combines sol-gel synthesis with self-assembly and phase separation to produce films with a tailored pore structure. Chapter 10 describes how nanomaterials can be used as soluble precursors for the preparation of extended... 

In a simplified view, the total flow is as follows (Fig. 8). Both soluble and membrane proteins that are translated at the membrane-bound ribosome are first localized at the ER. Some of them are transported to the Golgi apparatus, whereas others remain at the ER. At the Golgi apparatus, including the trans Golgi network (TGN), the next selection occurs some are transported to the plasma membrane, others to the endosome and to the lysosome/vacuole finally, and still others remain there. The lysosome is also an important organelle for the other transport system, the endocytic pathway. In this pathway, proteins at the plasma membrane are internalized by endocytosis. The sorting to lysosomes is treated in the next section. 

The composite materials have been used to form selective membranes for the separation of liquid mixtures [181]. The membranes should consist of a polymer which is soluble in the liquid components) to be separated, as the dispersed phase-derived polymer, and a continuous phase-derived polymer which is insoluble in all components of the liquid mixture. Thus, membranes consisting of polystyrene in polyacrylamide will separate toluene from cyclohexane, and those comprising polyacrylamide in crosslinked polystyrene can be used for water removal from ethanol. Due to the very thin films of polymer which separate the polyhedral dispersed phase cells, the permeation rates, which are measured by pervaporation, are relatively high. 

It is not surprising then that, despite its effectiveness, methotrexate therapy is underscored by serious side-effects and problems which have prompted ongoing research programmes to attempt the preparation of new analogues possessing better tumour-cell selectivity, lower toxicity, better transport properties, and improved lipid solubility and membrane permeability. These efforts have resulted in the preparation of thousands of analogues in which virtually every major area of the molecule has been varied and evaluated. 

The solubility selectivity of a membrane for a specific gas pair could be increased (in principle) by inducing specific interactions between the polymer and the more soluble component of the gas pair. For example, the substitution of certain polar groups in some rubbery polymers has been found to increase their solubility selectivity for CO2 relative to CH4 (Story and Koros, 1991 Koros, 1985). Unfortunately, the increase in the polarity of a polymer also tends to increase its chain packing density, and as a result, decreases the gas diffusivity in membranes made from that polymer. 

The essential part of an ISE is the ion-selective membrane that contains fixed or mobile sites that interact with ions in the solution. The membrane is commonly based on a plasticized polymer, glass, single crystal, or a sparingly soluble salt. The back-side of the membrane is in contact with a liquid- or solid-state ion-to-electron transducer that completes the ISE. New materials, such... 

Figure 5 Proteomics reveals functional secretory vesicle protein systems for neuropeptide biosynthesis, storage, and secretion. Chromaffin secretory vesicles (also known as chromaffin granules) were isolated and subjected to proteomic analyses of proteins in the soluble and membrane components of the vesicles. Protein systems in secretory vesicle function consisted of those for 1) production of hormones, neurotransmitters, and neuromodulatory factors, 2) generating selected internal vesicular conditions for reducing condition, acidic pH conditions maintained by ATPases, and chaperones for protein folding, and 3) vesicular trafficking mechanisms to allow the mobilization of secretory vesicles for exocytosis, which uses proteins for nucleotide-binding, calcium regulation, and vesicle exocytosis. These protein systems are coordinated to allow the secretory vesicle to synthesize and release neuropeptides for cell-cell communication in the control of neuroendocrine functions.

In measurements with ion-selective electrodes, interference by other ions is expressed by selectivity coefficients as in Eq. (17). If the nature of the ion-selective membrane is known, these interferences may easily be estimated. For example, in the determination of chloride with a Cl -selective electrode containing AgCl as the electroactive component in its membrane, concentrations of bromides or iodides (generally X ) must be controlled because they form less soluble silver salts than AgCl the solubility products of corresponding silver halides are used in Eq. (20) to estimate the selectivity coefficient ... 

In order to be used as an immunoassay label, an elec-trochemically active compound has to possess suitable electrochemical properties. It has to be soluble in aqueous media and should be stable in solution over a wide pH range. To be detectable, it must allow highly selective electrochemical detection or possess chemical properties to allow selective membranes to be used in the measurement electrode. 

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