Film coating processing problems

The hydrodynamic factors that influence the plasma polymerization process pose a complicated problem and are of importance in the application of plasma for thin film coatings. When two reaction chambers with different shapes or sizes are used and when plasma polymerization of the same monomer is operated under the same operational conditions of RF power, monomer flow rate, pressure in the reaction chamber etc., the two plasma polymers formed in the two reaction chambers are never identical because of the differences in the hydrodynamic factors. In this sense, plasma polymerization is a reactor-dependent process. Yasuda and Hirotsu [22] systematically investigated the effects of hydrodynamic factors on the plasma polymerization process. They studied the effect of the monomer flow pattern on the polymer deposition rate in a tubular reactor. The polymer deposition rate is a function of the location in the chamber. The distribution of the polymer deposition rate is mainly determined by the distance from the plasma zone and the... 

In GLC, separation occurs based on differences in partitioning of the sample components between the carrier gas and the liquid phase. A wide selection of liquid phases makes GLC a versatile separation technique. Further, the liquid phase can be a polymer or a chemically bonded phase. In all cases, the liquid phase is film coated or chemically bonded onto a solid support surface or a column wall. Liquid-bonded phases overcome the problem of leakage of the stationary phase material into the carrier. They are used commonly in LC also, and the process to fabricate... 

Particle deformation and polymer diffusion can only occur at temperatures above the glass transition temperature of the polymer. Final coatings, however, are required to be at temperatures considerably below the glass transition temperature. To get around this problem, it is common to add plasticizers to water borne latex dispersions to lower the glass transition temperature of the constituent polymer during the film formation process. Subsequent evaporation of the plasticizer results in a hard final coating. A common plasticizer is 2,2,4-trimethyl-l,3-pentanediol monoisobutyrate, usually referred to as Texanol Ester Alcohol. 

In coating processes the problem of controlling the flow of liquids down an inclined plate is a key question (Scriven 1960, Kretzschmar 1974). Therefore, the hydrodynamic flow of such films in combination with surface rheological and adsorption kinetics models were described. As the principle of a flowing film can be used also as a separate method to study adsorption processes in the range of milliseconds, the theory is presented here, while the experimental details are given in the next chapter. 

It is left as an exercise for the reader (Problem 9.10) to show that solving this equation for C oCy 0) and use of equations (9.3.23) and (9.3.38) lead to (9.3.39). For another rate-limiting process (e.g., diffusion of an electroreactant through a film coated on the electrode), the term k(E)Co(y — 0) would be replaced by the appropriate expression. This would yield an equation in the general form of the Koutecky-Levich equation, with the extrapolation to 0 allowing the determination of the kinetic parameter for that process [see, for example. Section 14.4.2]. 

The capillary flow example given is seen to be a one-parameter problem in which the parameter is the Bond number (Eq. 10.2.1). An important class of technical problems is coating flows, in which a uniformly thin liquid film is made to cover a substrate. For such flows a characteristic velocity is usually imposed on the substrate or the fluid. As a consequence, the behavior of the coating process generally depends on the capillary number and may depend on the Stokes number. Because of this distinction from the present example, and because of the technical importance of such flows, we shall treat them separately in the next section. 

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