Polymer coating membrane, permeability

Fig. 13 The controlled release of drug molecules from a (membrane-matrix) hybrid-type drug delivery system in which solid drug is homogeneously dispersed in a polymer matrix, which is then encapsulated inside a polymeric membrane, where D, P, and h are the diffusivity, permeability, and thickness, respectively, and the subscripts p, m, and d denote the drug depletion zone in the polymer matrix, polymer coating membrane, and diffusion layer, respectively.

Finally the synthesis of inorganic-polymer composite membranes should be mentioned. Several attempts have been made to combine the high permeability of inorganic membranes with the good selectivity of polymer membranes. Furneaux and Davidson (1987) coated a anodized alumina with polymer films. The permeability increased by a factor of 100, as compared to that in the polymer fiber, but the selectivities were low (H2/O2 = 4). Ansorge (1985) made a supported polymer film and coated this film with a thin silica layer. Surprisingly, the silica layer was found to be selective for the separation mixture He-CH4 with a separation factor of 5 towards CH4. The function of the polymer film is only to increase the permeability. No further data are given. 

H. Braun, F. Decker, K. Doblhofer and H. Sotobayashi, The redox-reaction [Fe(CN)6]3 /4 on electrodes coated with fixed charge polymer films - Observation of membrane permeability modulation by the electrode potential, Ber. Bunsenges. Phys. Chem., 1984, 88, 345-350 S-M. Oh and L.R. Faulkner, Luminescent and redox probes of structure and dynamics in quaternized poly(4-viniylpyridine) films on electrodes, J. Am. Chem. Soc., 1989, 111, 5613. 

Thin films with a broad spectrum of properties can be deposited in plasma chemical processes [30, 31]. Hard coatings such as diamond films and TiN films, soft plasma polymer films, insulating SiO films, highly conducting Si films, anti-reflection coatings, semi-permeable membranes and very effective diffusion barriers can be deposited. Important parameters for the film deposition are (i) the nature of the precursor, (ii) the gas mixture and... 

The aqueous permeability of coatings produced from smaller particle size polymers (D-30) was lower than the permeability of coatings produced from larger particles because of the lower porosities and higher densities achieved in D-30 coatings. Good permeability and selectivity of a membrane are commonly required in practical applications. 

In smaller scale research applications, a polymer-coated foil bag (polybag) can be vacuumed and the edges heat-sealed by hand [47]. An ideal sealant bag is thermally conductive, electronically insulating, moisture resistant, and has a one-way gas permeability membrane to vent gases generated from the system. 

The membrane can be semipermeable asymmetric membrane made from cellulose acetate or composite membranes made with dense thin polymer coating on a polystyrene support (see Figure 4.18). Asymmetric cellulose acetate membrane consists of a thin rejecting skin about 0.1 -0.5 pm thick integral with a much thicker porous substrate of 50-100 pm thick. The rejecting screen is permeable to water and relatively impermeable to various dissolved impurities, that is, salt ions and other small molecules that cannot be filtered. The permeability of the membrane depends on the construction of the membrane and the solute size. The skin offers hydraulic resistance to the flow. The porous substrate gives the membrane strength but offers... 

Doblhofer K, Lange R (1987) HexachlOToiridate(II]/IV) on polymer-coated electrodes. Investigation of the membrane permeability and the charge-transport mechanism. J Electroanal Chem Intefacial Electrochem 229 239-247... 

The predominant RO membranes used in water applications include cellulose polymers, thin film oomposites (TFCs) consisting of aromatic polyamides, and crosslinked polyetherurea. Cellulosic membranes are formed by immersion casting of 30 to 40 percent polymer lacquers on a web immersed in water. These lacquers include cellulose acetate, triacetate, and acetate-butyrate. TFCs are formed by interfacial polymerization that involves coating a microporous membrane substrate with an aqueous prepolymer solution and immersing in a water-immiscible solvent containing a reactant [Petersen, J. Memhr. Sol., 83, 81 (1993)]. The Dow FilmTec FT-30 membrane developed by Cadotte uses 1-3 diaminobenzene prepolymer crosslinked with 1-3 and 1-4 benzenedicarboxylic acid chlorides. These membranes have NaCl retention and water permeability claims. 

Fig. 1. Capsule permeability as measured by the inverse GPC method. Capsules were made from 1.25% A-carrageenan (Fluka) and 0.02% carboxymethylcellulose (Aqualon) in 0.9% sodium chloride (core polymers) and 2% polydimethylamine-co-epichlorohydrin modified, quater-nized (Scientific Polymer Products) and a quaternary amine (Agefloc B50, CPS) in PBS (receiving bath) using a 3 min reaction time. The capsules were subsequently washed with PBS, coated for 15 min with 0.1% LV alginate (Kelco) and again washed in PBS. Two molecular size dex-trans were used to probe the capsule permeability. 170 kD dextran is almost totally excluded while the lower molar mass polymers permeated the membrane to varying extents...

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