Synthetic membranes, solute transport

G. S. Park, Transport principles - solution, diffusion and permeation in polymer membranes in Synthetic Membranes Science, Engineering and Applications (Eds. P. M. Bungay, H. K. Lonsdale, M. N. Pinho), NATO ASI Series, D. Reidel Publishing, Dordrecht, Holland, 1986, pp. 

Other recent applications of AFM-SECM included the study of the iontophoretic transport of [Fe(CN)6]4 across a synthetic track-etched polyethylene terephthalate membrane by Gardner et al. [193]. They made the structure and flux measurements at the single pore level and found that only a fraction of candidate pore sites are active in transport. Demaille et al. used AFM-SECM technique in aqueous solutions to determine both the static and dynamical properties of nanometer-thick monolayers of poly(ethylene glycol) (PEG) chains end-grafted to a gold substrate surface [180]. 

Dendritic macromolecules exhibit compact globular structures which lead to their low viscosity in the melt or in solution. Furthermore, dendritic macromolecules are characterized by a very large number of available functional groups, which lead to unprecedented freedom for changing/tuning/tailoring the properties of these multivalent scaffolds via complete or partial derivatization with other chemical moieties. All these features have contributed to multidisciplinary applications of these unique macromolecular structures in recent years 6, 7). The development of efficient synthetic routes in recent years has given rise to a virtually unlimited supply of commercially available dendritic polymers, at very affordable price. The transport properties of hyperbranched and dendritic polymers have recently attracted attention as potentially new barrier and membrane materials 8-9). 

Reverse osmosis membranes are characterized by an MWCO of -100 Da, and the process involves transmembrane pressures (TMP) of 10-50 bar (1000-5000 kPa), which are 5-10 times higher than those used in UF [11,36]. Unlike UF, the separation by RO is achieved not by the size of the solute but due to a pressure-driven solution-diffusion process [36]. Like UF membranes, RO membranes are uniquely stmctured films from synthetic organic polymers and consist of an ultrathin skin layer superimposed on a coarsely porous matrix [3]. The skin layer of the RO membrane is nonporous, which may be treated as a water-swollen gel, and water is transported across membrane by dissolving in this gel and diffusing to the low-pressure side... 

Several investigators have demonstrated the feasibility of immobilized liquid membrane gas separations in applications where large pressure differences are encountered such as acid gas removal from synthetic natural gas. The immobilized liquid membranes prepared by Kimura et al. (16) using 100 pm cellulose acetate supports withstood CO2 partial pressure differences of up to 6.89 10 N/m. Matson et al. (15) used mlcroporous cellulose acetate and polyethersulfone films of 25-75 pm thickness to successfully immobilize potassium carbonate solutions for H2S transport at pressure differences of up to 2.07 10 N/m. The ILMs were supported by macroporous non-wetting polymer films such as polypropylene and polytetrafluoro-ethylene to increase the resistance to high transmembrane pressures. 

One of the main functions of the plasma membranes of living cells is to control the transport processes into and out of the cells of many substances and thus to regulate the composition of the intracellular fluid. The fluid usually contains solutes at concentrations which are quite different from their corresponding values in the bathing medium. This is achieved by the ability of the membrane to discriminate among various solutes so that some are allowed through, others are kept inside or outside the cell, and still others are carried actively. In addition, important processes such as oxidative metabolism, protein synthesis and several other synthetic processes are intimately connected with and dependent on membrane processes. In fact, continued existence of the cell is critically dependent on its having a functional plasma membrane. 

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