Expanded film membranes

The original expanded film membranes were sold ia roUs as flat sheets. These membranes had relatively poor tear strength along the original direction of orientation and were not widely used as microfiltration membranes. They did, however, find use as porous inert separating barriers ia batteries and some medical devices. More recentiy, the technology has been developed to produce these membranes as hoUow fibers, which are used as membrane contactors (12,13). 

Expanded-film membranes, 15 802-803 Expanded graphite, 12 794-795 Expanders, in nitric acid production, 17 178... 

Figure 2.29 Scanning electron micrographs at approximately the same magnification of four microporous membranes having approximately the same particle retention, (a) Nuclepore (polycarbonate) nucleation track membrane (b) Celgard (polyethylene) expanded film membrane (c) Millipore cellulose acetate/cellulose nitrate phase separation membrane made by water vapor imbibition (Courtesy of Millipore Corporation, Billerica, MA) (d) anisotropic polysulfone membrane made by the Loeb-Sourirajan phase separation process...

Expanded-film membranes are made from crystalline polymers by an orientation and annealing process. A number of manufacturers produce porous membranes... 

Fig. 5. (a) Preparation method and (b) scanning electron micrograph of a typical expanded polypropylene film membrane, ia this case Celgard. 

Arteriovenous shunt PTEE Expanded film ePTEE membrane... 

Cince the introduction by Mueller et al. (11) of a method for producing black lipid films, the study of black lipid films has expanded rapidly. Numerous publications have appeared in which these films are used to study physicochemical properties, others in which they are used as a model for biological membranes. Survey articles have been published by Mueller et al. (12), by Thompson (18), and more recently by Tien and Dawidowicz (19). As a model for a cellular membrane the black lipid film is bound to be a poor model since it lacks an essential part of even the simplest membrane conception, the polyelectrolyte coating. One of the few properties of black lipid membranes within biological ranges is its water permeability (4, 5, 6, 20). 

In the submicron range of particle sizes, there are at least two media types to consider depth and microporous membrane. Typically, depth media is melt-blown fibrous nonwoven type (Fig. 18.13). Membranes are basically cast or expanded microporous films. Depth filters with a wrapped or pleated construction are used for slurry filtration (see Fig. 18.14a and b). Membrane... 

A mixed monolayer consisting of stearic acid (9.9%), palmitic acid (36.8%), myristic acid (3.8%), oleic acid (33.1%), linoleic acid (12.5%), and palmitoleic acid (3.6%) produces an expanded area/pressure isotherm on which Azone has no apparent effect in terms of either expansion or compressibility (Schuckler and Lee, 1991). Squeeze-out of Azone from such films was not reported, but the surface pressures measured were not high enough for this to occur. The addition of cholesterol (to produce a 50 50 mixture) to this type of fatty acid monolayer results in a reduction of compressibility. However, the addition of ceramide has a much smaller condensing effect on the combined fatty acids (ratio 55 45), and the combination of all three components (free fatty acids/cholesterol/ceramide, 31 31 38) produces a liquid condensed film of moderate compressibility. The condensed nature of this film therefore results primarily from the presence of the membrane-stiffening cholesterol. In the presence of only small quantities of Azone (X = 0.025), the mixed film becomes liquid expanded in nature, and there is also evidence of Azone squeeze-out at approximately 32 mN m. ... 

When a membrane expands and the concentration of a surfactant at the interface decreases, there exist two mechanisms to restore the surfactant surface concentration. The first mechanism, termed the "Marangoni effect" (16), refers to the fact that the surface flow can drag with it some of the underlying layers, i.e. the surface layer can flow from areas of low surface tension, thus restoring the film thickness. It is also a source of film elasticity or resilience. 

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