Hydrophobic fluoropolymers

The comingled hydrophobic fluoropolymers PTFE, FEP, and sometimes ethylene tetrafluoroethylene and perfluoroalkoxy resin yield different hydrophobic character and surface chemistry within the carbon-fiber matrix. This treatment creates a balance... 

The focus of this section is on the corrosion phenomena of the GDL substrate graphite fibers driven by solid-liquid surface chemical interactions and surface energetics. Particular importance is assigned to uncoated areas of fibo s by hydrophobic fluoropolymer and interfacial zones between fiber and fluoropolymer. Since Teflon products such as PTFE and FEP are known to have excellent thermal resistance, electrochemical corrosion stability, chemical durability, and mechanical properties, the GDL and MPL fluoropolymer phase is not considered to be vulnerable in a PEFC operating enviromnent. 

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. 

Example 7.10. Prins et al. [306] used electrowetting to control fluid motion in microchannels. To do so, they coated aluminum electrodes first with a 12 pm thick layer of parylene and then with a 10 nm thick fluoropolymer film. The channels were 0.35 mm wide. Due to the hydrophobic polymer water does not flow into the capillaries. Only after applying voltages of typically 200 V did the capillaries fill with water. When switching the voltage off, the water flowed out of the capillaries again. 

Virtually the entire membrane manufacture today is based on laminate structures comprising a thin barrier layer deployed upon a much thicker, highly permeable support. Most are formed of compositionaUy homogeneous polysulfone, cellulose acetate, polyamides, and various fluoropolymers by phase inversion techniques in which ultrathin films of suitably permselective material are deposited on prefabricated porous support structures. Hydrophobic polymers as polyethylene, polypropylene, or polysulfone are often used as supports. A fairly comprehensive hst of microporous and ultrafiltration commercial membranes and produced companies are presented in Refs [107-109]. A review on inorganic membranes has been given in Ref. [110]. 

Hydrophobic polysulfones, polyolehns, carbon. Life polymers 1 to 2 years fluoropolymers <4 years. 

Poly(vinylidene fluoride) (PVDF) has been recently tested as the base polymer in ionic liquid (IL)-based PIMs [13-15]. PVDF is a thermoplastic fluoropolymer with high hydrophobicity, good chemical resistance, and excellent thamal and mechanical stability making it attractive as a base polymer for PIMs. 

In addition to Nafion, the family of sulfonated fluoropolymers includes Dow chemical membranes and Membrane C. Weber and Newman predict that the clusters formed within Dow membranes are smaller than in Nafion due to the higher elastic deformation energy [27]. For sulfonated polyetherketone membranes, which are under investigation due to their potential in lowering costs, separation into hydrophobic and hydrophilic domains is not as well defined as in Nafion [28]. As a result, their structure consists of narrower channels and clusters that are not as well connected as in Nafion [27, 28]. 

Compared to fluoropolymers, aliphatic and aromatic polymers are less hydrophobic, and the sulfonic acid functional group is less acidic and less polar. Nafion is a superacid, with a piCa -6 as estimated using pJCa database 4.0 [130]. Ma et al. [131] determined the pKa of Nafion 117 and the sulfonated aromatic polymer, BPSH (Scheme 3b), to be -3.09 and -2.04, respectively, while the simplest aromatic sulfonic acid, benzene sulfonic acid, has a pJCa of 0.70 [132]. Aromatic polymers are more rigid than Nafion and possess shorter ionic side chains, and therefore are expected to exhibit a lesser degree of separation between hydrophilic and hydrophobic domains. SAXS measurements on rigid aromatic polymers, such as SPIs based on naphthalenic dianhydride (Scheme 3k, x = 5, xly = 30/70) indicate the ab-... 

Here we describe two simple fabrication processes to modify the surface of the device to achieve a very high water contact angle. In the first approach, the device was first coated with a thin film of hydrophobic materials, fluoropolymer in this case, and then oxygen plasma was used to create superhydrophobic surfaces. However, only in some cases, the chemical properties of the hydrophobic materials could be altered by the oxygen plasma treatment [19]. Therefore, a second technique has been developed where the nanostructures can be created on the device surfaces by a nanoimprint process [20]. Both of these approaches are compatible with the micro-fabrication process. 

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