Membranes hydrophilic coating

Two important features emerge from our examination of these three examples of membrane protein structure. First, the parts of the protein that interact with the hydrophobic parts of the membrane are coated with nonpolar amino acid side chains, whereas those parts that interact with the aqueous environment are much more hydrophilic. Second, the structures positioned within the membrane are quite regular and, in particular, all backbone hydrogen-bond donors and acceptors participate in hydrogen bonds. Breaking a hydrogen bond within a membrane is quite unfavorable, because little or no water is present to compete for the polar groups. 

Klein E, Eichhloz E, and Yeager DH. Affinity membranes prepared from hydrophilic coatings on microporous polysuffone hoUow fibers. J. Membr. Sci. 1994 90 68-80. 

The membrane is exposed to chlorine and brine on one side and strong caustic solution on the other side at temperatures of around 90 °C. Only ion-exchange membranes made of perfluoropolymer can withstand such severe conditions. The ion-exchange groups are sulfonate (SOf) or carboxylate (CHCOO-). Modern membranes of this kind consist of three layers, a carboxylic layer on the cathode side, a sulfonate layer on the anode side and a reinforcement layer of fabric in between. In addition, both sides are provided with a hydrophilic coating [3, p. 81 15]. The thickness of the membrane is only one- to two-tenth of a millimeter. It must be mentioned that the hydrate water of the cations is taken along through the membrane. 

Zeolite membranes have been demonstrated for many applications. Applications such as separation membranes, membrane reactors, adsorption, and catalysis have been covered in several reviews. In this entry, we focus on new applications including sensors, low-dielectric constant (low-k) films, corrosion resistant coatings, hydrophilic coatings, heat pumps, and thermoelectrics. 

Osczevski and Dolhan [16] and Farnworth et al [17] reported a strong dependency of water vapour resistance of hydrophilic membranes or coatings the higher the relative humidity at the membrane, the lower the water vapour resistance (i.e., the higher the water vapour permeability or breathability). 

The main property of the outer shell is to provide a protection against the outside weather conditions, mainly rain, snow and wind. In order to avoid excessive sweat accumulation, the outer layer should allow moisture transfer from the body to the environment. Such waterproof, windproof and breathable fabrics (WBF—mainly membranes and coatings) have been on the market for more than 30 years. The waterproof properties and, at the same time, the water vapour transfer are either achieved with a micro-porous or a hydrophilic structure, or a combination of both technologies (bi-component WBF). Waterproofness and breathability are contradictory requirements and, therefore, a compromise has to be found between protection and comfort properties. This compromise is usually achieved by adapting the porosity and thickness of such WBF layers. 

The interaction of the solutes with the membrane surface is normally characterized by the membrane hydrophilicity/hydrophobicity and a fixed charge using a contact angle measurement and a streaming potential, respectively. In this study, AFM was used to determine the force of adhesion between a HA-coated silica probe (illustrated in Figure 5.27) and the membrane surface. A typical force measurement... 

Wang et al. (2002) demonstrated a composite membrane (subjected to PV) of an asymmetric poly(4-methyl-l-pentene) (TPX) membrane dip-coated with poly(acrylic acid) (PAA). To improve the interface peeling of the PA A/TPX composite membranes, the surfaces of TPX membranes were modified by residual air plasma in a tubular-type reactor. The plasma treatments were effective in rendering the asymmetric TPX membrane hydrophilic. Optimal results were obtained with PAA/TPX composite membrane prepared from the PAA/ethylene glycol (EG)/aluminum nitrate = 1/2/0.05 coating solution at 5 W/30 s plasma treatment condition. Concentration of the water in the permeate was nearly 100%, and a permeate flux of 960 g/m h was obtained with a 3 wt% feed acetic acid concentration. 

He, T., Mulder, M.H.V, Strathmann, H. Wessling, M. (2002) Preparation of composite hollow fiber membranes co-extrusion of hydrophilic coatings onto porous hydrophobic support structures. Journal of... 

Polyurethane hydrogels are widely used in soft contact lenses, controlled release devices, semipermeable membranes and hydrophilic coatings (66). The properties of polyurethane hydrogels can be varied by variation of their components, such as the polyols, diisocyanate, chain extender, or cross-linker (67-69). Because of the excellent mechanical and physical properties, polyurethanes are widely used in medical applications such as coating for medical devices for preventing protein adsorption (70, 71). 

Unlike hydrophobic CLs, hydrophilic CLs use a hydrophilic perfluorosulfonate ionomer (PFSI) such as Nafion as a binder instead of PIPE. Hence, this kind of CL can be called an ionomer-bonded hydrophilic CL. During preparation, the catalyst powder (e.g. Pt/C), PFSI (e.g. Nafion ), and solvent (e.g. ethanol or isopropanol) are mixed thoroughly to form a uniform hydrophilic catalyst ink/paste that is then transferred to a GDL or a membrane. Hydrophilic CLs can be classified into two groups, according to the transfer method GDL-based hydrophilic CL and catalyst coated membrane (CCM). 

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