Applications microporous films

Malfatti, L. Falcaro, P Amenitsch, H. Caramori, S. Argazzi, R. Bignozzi, C. A. Enzo, S. Maggini, M. Innocenzi, P. 2006. Mesostructured self-assembled titania films for photovoltaic applications. Microporous Mesoporous Mater. 88 304-311. 

For the sake of discussion, we have divided the separators into six types—microporous films, non-wovens, ion exchange membranes, supported liquid membranes, solid polymer electrolytes, and solid ion conductors. A brief description of each type of separator and their application in batteries are discussed below. 

Until quite recently, most of me facilitated transport results reported in me literature were obtained with supported liquid membranes held by capillarity in microporous films. The instability of these membranes has inhibited commercial application of me process. Three factors contribute to mis instability and me consequent loss of membrane performance over time ... 

Mintova S and Bein T. Nanosized zeolite films for vapor-sensing applications. Micropor Mesopor Mater 2001 50(2-3) 159-166. Osada M, Sasaki I, Nishioka M, Sadakata M, and Okubo T. Synthesis of a faujasite thin layer and its application for SO2 sensing at elevated temperatures. Micropor Mesopor Mater 1998 23(5-6) 287-294. 

Monomers, such as n-vinyl pyrrolidinone and hydroxy ethyl methacrylate, have been used to enhance the biocompatibility of films and to control the air permeation and hydrophilicity of microporous films and of non-woven polyolefin materials [10], Significant opportunities exist to pursue other uses in the bio-materials area [11, 12], Attempts to produce grafted films to control gas permeation for use in food packaging applications have not met with success [13], Co-extruded films have proven to be more acceptable in this food packaging area. The modification of films and non-woven materials rely upon low-voltage, self-shielded electron beams. The development of lower cost, low-voltage EB equipment reduces the economic barriers to further development in this area (Fig. 4) [14, 15],... 

The neutral, microporous films represent a very simple form of a membrane which closely resembles the conventional fiber filter as far as the mode of separation and the mass transport are concerned. These membranes consist of a solid matrix with defined holes or pores which have diameters ranging from less than 2 nm to more than 20 //m. Separation of the various chemical components is achieved strictly by a sieving mechanism with the pore diameters and the particle sizes being the determining parameters. Microporous membranes can be made from various materials, such as ceramics, graphite, metal or metal oxides, and various polymers. Their structure may be symmetric, i.e., the pore diameters do not vary over the membrane cross section, or they can be asymmetrically structured, i.e., the pore diameters increase from one side of the membrane to the other by a factor of 10 to 1,000. The properties and areas of application of various microporous filters are summarized in Table 1.1. 

Pina MP, Mallada R, Arruebo M, Urbiztondo M, Navascuds N, de la Iglesia O, and Santamaria J. Zeolite films and membranes. Emerging applications. Micropor. Mesopor. Mat. 2011 144 19-27. 

Mintova S, Bein T. Nanosized zeolite films for vaporsensing applications. Micropor Mesopor Mater 2001 50(2-3) 159-166. 

Typical applications automotive/transportation, apphance, films, closures, tapes/stripes, opaque and matte finish oriented film, breafhable, microporous film, opaque thermoformed parts, and opaque or translucent injection molded parts, foam, food packaging film, overwrap film, bottles and rigid articles, food trays, tubing... 

Microporous Polyethylene Films. Disposable IR cards are available to which samples can be directly applied for infrared analysis (Fig. 8.8). These convenient IR cards have two 19-mm circular apertures containing a thin microporous film of chemically resistant polyethylene. Cards having microporous polytetrafluoroethylene are also available for special applications. The cards with polyethylene films may be used for infrared analysis from 4000-400 cm except for the region of aliphatic C-H stretching that occurs between 3000-2800 cm In this region of an FT-IR spectrum, there are several sharp... 

D. Ansari, A. Calhoun and P. Merriman, The Role of Calcium Carbonate in Microporous Film Applications, Imerys Technical Data Sheet PMA 124PL - 2nd Edition, Imerys Performance Minerals, Cornwall, UK, 2001. 

Separator structures fall into four main categories microporous films, nonwovens, gel polymers, and solid polymers. Microporous films contain small pores (5 to 10 nm in diameter) and are often used for low temperature applications. They are made from nonwoven fibers such as cotton, polyester, glass, polyolefins (PP and PE), PTFE, and PVC. Microporous separators are commonly used with organic electrolytes and in acidic systems. Nonwovens are manufactured as mats of fibers and bind through frictional forces. They exhibit consistent weight, thickness, and degradation resistance but they show inadequate pore order and are difficult to make thinner than 25 pm. Nonwovens are generally made from cellulose, PTFE, PVC, PVdF, or a combination of polyolefins and receive preference in alkaline systems [114]. 

Pina, M.P., Mallada, R., Arruebo, M. et al. (2011) Zeolite films and membranes Emerging applications. Microporous and Mesoporous Materials, 144, 19-27. 

The discussion so far implies that membrane materials are organic polymers, and in fact most membranes used commercially are polymer-based. However, in recent years, interest in membranes made of less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafiltration and microfiltration applications for which solvent resistance and thermal stability are required. Dense, metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported liquid films are being developed for carrier-facilitated transport processes. 

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. 

Microporous silicon is suitable for sacrificial layer applications because of its high etch rate ratio to bulk silicon, because it can be formed selectively, and because of the low temperatures required for oxidation. PS can be formed selectively if the substrate shows differently doped areas, as discussed in Section 4.5, or if a masking layer is used. Noble metal films can be used for masking as well as Si02, Si3N4 and SiC. Oxidation conditions are given in Section 7.6, while the etch rates of an etchant selective to PS are given in Fig. 2.5 b. 

Kikuchi, E., S. Uemiya, N. Sato, H. Inoue, H. Ando and T. Matsuda. 1989. Membrane reactor using microporous glass-supported thin film of palladium Application to the water gas shift reaction. Chem. Lett. 3 489-492. 

Geong and coworkers reported a new concept for the formation of zeolite/ polymer mixed-matrix reverse osmosis (RO) membranes by interfacial polymerization of mixed-matrix thin films in situ on porous polysulfone (PSF) supports [83]. The mixed-matrix films comprise NaA zeoHte nanoparticles dispersed within 50-200 nm polyamide films. It was found that the surface of the mixed-matrix films was smoother, more hydrophilic and more negatively charged than the surface of the neat polyamide RO membranes. These NaA/polyamide mixed-matrix membranes were tested for a water desalination application. It was demonstrated that the pure water permeability of the mixed-matrix membranes at the highest nanoparticle loadings was nearly doubled over that of the polyamide membranes with equivalent solute rejections. The authors also proved that the micropores of the NaA zeolites played an active role in water permeation and solute rejection. 

The most common material used is cellophane, which is a cellulose film, which acts as a membrane and is capable of resisting zinc penetration. The cycle life of cells utilizing this material is severely limited due to the hydrolysis of the cellophane in alkaline solution. Various methods have been tried to stabilize cellulose materials, such as chemical treatment and radiation grafting to other polymers, but none have, as of now proved economically feasible. The most successful zinc migration barrier material yet developed for the nickel—zinc battery is Celgard microporous polypropylene film. It is inherently hydrophobic so it is typically treated with a wetting agent for aqueous applications. 

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