Films microporous

Fig. 15. Schematic of the interfacial polymerization process. The microporous film is first impregnated with an aqueous amine solution. The film is then treated with a multivalent cross-linking agent dissolved in a water-immiscible organic fluid, such as hexane or Freon-113. An extremely thin polymer film...

Nonwoven materials have not been able to compete with microporous films, most probably because of the difficulty in mak ing thin (25pm) nonwovens with acceptable physical properties (for example,... 

The schematic diagram of a gas-sensing electrode is illustrated in Figure 16.8, that comprises of essentially a reference electrode (E), a specific-ion electrode (B), and an internal electrolyte solution (F) contained in a cylindrical plastic tube (G). One end of the plastic tubing is provided with a thin, replaceable, gas-permeable membrane that separates the internal electrolyte solution from the external solution containing gaseous analyte. However, the exact composition and specifications of this gas-permeable membrane is usually described by its respective manufacturers. It is normally made up of a thin microporous film fabricated from a hydrophobic plastic material. 

QC in silicon structures requires dimensions of a few nanometers and is therefore proposed to be responsible for the formation of microporous films on Si electrodes, as discussed in Chapter 7. QC is independent of doping and is often found as a superposition to pore formation by SCR effects. Only for p-type silicon electrodes of doping densities of 1016-1017 cm-3 is no formation of SCR-related pores observed upon anodization in aqueous HF. This substrate doping regime is therefore best suited for formation of purely microporous layers. 

Improvements based on Bellcore technology were reported recently by Wunder and co-workers. Using PEG oligomers instead of DBP, they obtained the PVdF—HFP microporous films with the pore size increased from nanoscale to microscale, as shown in... 

In most batteries, the separators are either made of nonwoven fabrics or microporous polymeric films. Batteries that operate near ambient temperatures usually use separators fabricated from organic materials such as cellulosic papers, polymers, and other fabrics, as well as inorganic materials such as asbestos, glass wool, and Si02. In alkaline batteries, the separators used are either regenerated cellulose or microporous polymer films. The lithium batteries with organic electrolytes mostly use microporous films. 

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. 

The materials used in nonwoven fabrics include a single polyolefin, or a combination of polyolefins, such as polyethylene (PE), polypropylene (PP), polyamide (PA), poly(tetrafluoroethylene) (PTFE), polyvinylidine fluoride (PVdF), and poly(vinyl chloride) (PVC). Nonwoven fabrics have not, however, been able to compete with microporous films in lithium-ion cells. This is most probably because of the inadequate pore structure and difficulty in making thin (<25 /rm) nonwoven fabrics with acceptable physical properties. 

Table 3. Manufacturing Process of Typical Microporous Film ...

Polypropylene and polyethylene microporous films obtained by this method are available from Cel-gard48.5o,54,55 Ube. The dry process is technologically convenient because no solvents are required. However, only a uniaxial stretching method has been successful to date, and as a result, the pores are slitlike in shape and the mechanical properties of films are anisotropic. The tensile strength in the lateral direction is relatively low. 

Producing polyethylene microporous film with a porosity of 20 to 80% for battery separators. ... 

As current is drawn from the cell, the positive electrode voltage is depressed due to concentration polarization as sulphuric acid within the pores is consumed. This effect is more marked for partially discharged cells. Formation of lead sulphate decreases the pore volume and produces a microporous film on the Pb02 matrix. 

Figure 3.20 Schematic of the interfacial polymerization process. The microporous film is first impregnated with an aqueous amine solution. The film is then treated with a multivalent crosslinking agent dissolved in a water-immiscible organic fluid, such as hexane or Freon-113. An extremely thin polymer film forms at the interface of the two solutions [47]. Reprinted from L.T. Rozelle, J.E. Cadotte, K.E. Cobian, and C.V. Knopp, Jr, Nonpolysaccharide Membranes for Reverse Osmosis NS-100 Membranes, in Reverse Osmosis and Synthetic Membranes, S. Sourirajan (ed.), National Research Council Canada, Ottawa, Canada (1977) by permission from NRC Research Press...

Carrier facilitated transport membranes incorporate a reactive carrier in the membrane. The carrier reacts with and helps to transport one of the components of the feed across the membrane. Much of the work on carrier facilitated transport has employed liquid membranes containing a dissolved carrier agent held by capillary action in the pores of a microporous film. 

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 ... 

Finally, we will consider briefly the formation of multilayer thin films by layer-by-layer deposition of hydrogen-bonded polymer pairs [51,52]. In this way a multilayer structure is obtained from potentially miscible polymer pairs. The stability of these films very much depends on the presence of hydrogen bonds, and pH may be used as an external trigger to erase the layered structure [53,54] and selectively dissolve one of the components [25-27]. This procedure allows for the preparation of microporous films not unlike the nanoporous films obtained by dissolution of the hydrogen-bonded side groups from self-assembled block copolymer-based comb-shaped supramo-lecules [15,17,18]. 

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... 

Figure 1. Schematic representation of operation of heterogeneous liquid crystal light shutters A) glass beads in a liquid crystal film, B) liquid crystal imbibed in a microporous film, C) encapsulated liquid crystal, D) polymer dispersed liquid crystals.

Si02 microporous film on alumina 2.0-5.0x10 35-200 de Lange [59-63] thickness 100 nm AP = 1 bar... 

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