Porous substrate coating

Structure EANPS = electrostatic agglomerated nonporous substrate, EAWPS = electrostatic agglomerated wide-pore substrate, PGPS = polymer grafted porous substrate, SMPSS = silane modified porous silica substrate, CMS = chemically modified substrate, APCS = adsorbed polymer coated substrate. 

These types of separators consist of a solid matrix and a liquid phase, which is retained in the microporous structure by capillary forces. To be effective for batteries, the liquid in the microporous separator, which generally contains an organic phase, must be insoluble in the electrolyte, chemically stable, and still provide adequate ionic conductivity. Several types of polymers, such as polypropylene, polysulfone, poly(tetrafluoroethylene), and cellulose acetate, have been used for porous substrates for supported-liquid membranes. The PVdF coated polyolefin-based microporous membranes used in gel—polymer lithium-ion battery fall into this category. Gel polymer... 

An early generation of composite membranes, developed by Riley, et al. (21), was based on cellulose triacetate (CTA) cast in an ultrathln coat from chloroform on the finely porous surface of a cellulose nitrate/cellulose acetate substrate. These membranes did not reflect a need for a hydrophllic-gel Intermediate layer. Yet, this membrane substrate is much more hydrophilic than the rejecting CTA layer, and high flux as well as high separation were concurrently obtained. This is not the case if the porous substrate is highly hydrophobic. A rejecting layer deposited on such a surface would yield an extremely poor productivity due to the loss of... 

In the field of metallic powder applications, a method of plasma spray coating suitable for biomedical materials has been developed using titanium and calcium phosphate composite powder. By means of the mechanical shock process, the appropriate composite powder was prepared, and plasma sprayed on Ti substrate under a low-pressure argon atmosphere. A porous Ti coating layer was obtained in which the surface and the inside of the pores were covered thinly with hydroxyapatite. This surface coating is expected to show excellent bone ingrowth and fixation with bone (21). 

Sometimes primers can take the place of surface treatments. Two examples are with porous substrates and with certain plastic substrates. With weak porous substrates, such as wood, cement, or porous stone, the primer can be formulated to penetrate and bind weakly adhering material to provide a new, tightly anchored surface for the adhesive. Chlorinated polyolefin primers will increase the adhesion of coatings and adhesives to polypropylene and to thermoplastic olefins. The chlorine atoms in the outer surface of the primer increase surface energy and enhance adhesion of adhesives, sealants, and paints. 

Using inkjet special substrate coatings is, most probably, the most widely used method to enhance inkjet printing quality for the SOHO (Small Office Home) markets. However, when dealing with commercial printing, e.g., wide format printers or non-porous substrates, top coats will neither guarantee the performance required by commercial customers, nor meet the cost goal required for most applications. 

Permeable layer reactors consist of thin, porous metal or ceramic substrates onto which titanium dioxide is coated in a manner that allows for flowing fhrough the porous substrates. The flow can be either perpendicular to the surface of the porous media or alternatively may combine perpendicular and parallel vectors. An example of such a reactor was presented by Tsuru et al. (2006). Here, a titania membrane (pore sizes 2.5-22 nm) was prepared... 

FIGURE 25.8 SEM images of the ferromagnetic composite membranes prepared by impregnation of porous substrates (a) silica-coated y-FejOj (b) Fe2Co04. 

In addition to the dip-coating method, ceramic layers on a porous substrate can also be formed by filtration of a sol or by filtration of a suspension using the substrate as a filter and applying an external pressure. These methods are not discussed in this chapter. The reader is referred to Ref. [1] for more information. 

Dip dispersion coating is a colloid processing technique used as a method for the preparation of coatings. There are two possible compaction modes when a porous substrate is withdrawn from a dispersion ... 

Film-coating is the formation of an adhering dispersion layer as a result of the drag force exerted by the substrate during withdrawal from a dispersion. To achieve pure fihn-coating, the capillary suction of the porous substrate must be suppressed. The thickness of the entrained dispersion layer increases with increasing withdrawal speed and increasing dispersion viscosity. The contact... 

In this chapter we have seen that application of porous ceramic coatings on porous substrates for preparing membrane supports is a complex process. Every step has to be carried out successfully to obtain substrates or membranes themselves which fulfil the requirements. We have seen that models of the coating processes are useful but still far from capable of describing the processes completely. We have seen that specific aspects such as prevention of defect formation still defy quantitative and sometimes also qualitative understanding. We have seen that sccding-up is not a trivial matter and that much work has to be performed to enable successful preparation of large surface areas. 

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