Hydrophilicity, inorganic membranes

A number of differenf approaches have been used to try to overcome some of these disadvantages of existing membranes. One such approach is to try to prevent water loss from the proton transport pathways, thus maintaining proton conductivity above the boiling point of wafer. Typically, this is attempted by adding hydrophilic inorganic species into the membrane. Furthermore, these particles in themselves may also be capable of proton conduction. 

One final example of multiple layer MPL was presented by Karman, Cindrella, and Munukutla [172]. A four-layer MPL was fabricated by using nanofibrous carbon, nanochain Pureblack carbon, PIPE, and a hydrophilic inorganic oxide (fumed silica). The first three layers were made out of mixtures of the nanofibrous carbon, Pureblack, carbon, and PTFE. Each of these three layers had different quantities from the three particles used. The fourth layer consisted of Pureblack carbon, PTPE, and fumed silica to retain moisture content to keep the membrane humidified. Therefore, by using these four layers, a porosity gradient was created that significantly improved the gas diffusion through the MEA. In addition, a fuel cell with this novel MPL showed little performance differences when operated at various humidity conditions. 

Organic and inorganic membranes have in common that the membrane materials can be selected ranging fi om hydrophilic to hydrophobic. For dissolution and adsorption the sirrqrle rules "like dissolves like" and "like adsorbs like" apply. 

Polymeric microporous hydrophobic membranes, typically polytetra-fiuoroethylene (PTFE), polypropylene (PP) and polyvinylidenefluoride (PVDF), are major membrane materials. Modified hydrophilic membranes such as cellulose acetate and cellulose nitrate modified with plasma polymerisation, have also been successfully tested in MD operations (Lawson and Lloyd, 1997). Furthermore, modified inorganic membranes, such as ceramic membrane modified with CgFi7(CH2)2Si(OC2H5)3 perfluoroalkylsi-lane molecule (Cg) and carbon nanotube based membranes, have also been developed for MD (Susanto, 2011). 

The parameters and consequently the efficiency of PV strongly depends on the properties of the membrane material. Common membrane materials are various dense polymers and microporous inorganic membranes (zeolithes, silica,. ..) either with hydrophilic or organophilic character. Furthermore composite membranes offer the possibility to combine different materials for the dense active layer and the porous support layer. Besides membrane material fluid hydrodynamics influences the efficiency of separation. The pressure drop especially on the permeate side reduces the driving force of the most permeating components. 

As a final step, the surfaces of the membranes can be coated with hydrophilic inorganic porous layers, so as to enhance the release of the gas bubbles generated in the electrolysis cells. 

Zeolite membranes represent a new branch of inorganic membranes. Significant progress has been made so far in the synthesis of thin, high-flux, defect-free zeolite membranes with new techniques of preparation and modification. In fact, the hydrophilic LTA zeolite membranes have already been applied in industry for dehydration from organic solutions... 

In the ease of hydrophilic membranes (as most of the inorganic membranes are), when using liquids like those already mentioned, it is reasonable to suppose zero eontact angle (or nearly). The same calculation procedure described for gas-liquid interfaee ean be used to calculate the differential flux and pore number distributions. 

Since some structural and dynamic features of w/o microemulsions are similar to those of cellular membranes, such as dominance of interfacial effects and coexistence of spatially separated hydrophilic and hydrophobic nanoscopic domains, the formation of nanoparticles of some inorganic salts in microemulsions could be a very simple and realistic way to model or to mimic some aspects of biomineralization processes [216,217]. 

Membranes UF membranes consist primarily of polymeric structures (polyethersulfone, regenerated cellulose, polysulfone, polyamide, polyacrylonitrile, or various fluoropolymers) formed by immersion casting on a web or as a composite on a MF membrane. Hydrophobic polymers are surface-modified to render them hydrophilic and thereby reduce fouling, reduce product losses, and increase flux [Cabasso in Vltrafiltration Membranes and Applications, Cooper (ed.). Plenum Press, New York, 1980]. Some inorganic UF membranes (alumina, glass, zirconia) are available but only find use in corrosive applications due to their high cost. 

Yang et al. [294] determined nanomolar quantities of individual molecular weight amines (and organic acids) in sea water. Amines were diffused from the sample across a hydrophilic membrane to concentrate and separate them from inorganic salts and most other dissolved organic compounds. Methylamine, dimethylamine, and trimethylamine were all found in measurable amounts in sea water. 

Inorganic compounds - Shi et al. [24] reported that they know of no inorganic chemicals (chemicals lacking carbon) that bind ER and result in endocrine disruption. Although ER binding may be possible in some cell-free systems, these inorganic compounds may be too hydrophilic to cross a cell membrane and... 

The design of artificial self-organizing systems is based on the ability of some molecules which contain simultaneously hydrophobic and hydrophilic groups to form molecular assemblies of definite structure in solution. Examples of the assemblies that can be used to suppress undesirable recombination processes are polyelectrolytes, micelles, microemulsions, planar lipid membranes covering an orifice in a film separating two aqueous solutions, unilamellar vesicles, multilamel-lar vesicles and colloids of various inorganic substances (see reviews [8-18] and references therein). 

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