Diffusion coatings continued processes

Emulsion polymerization is similar to suspension polymerization in the sense that the reaction also takes place in the presence of a water phase and the applied monomer forms a second liquid phase. However, in this case the added radical initiator is not soluble in the monomer droplets but in the water phase. To allow the monomer to come into contact with the initiator an emulsifier is added to the reaction mixture that creates micelles in the systems. By diffusion processes both monomer molecules and initiator molecules reach the micelle. Polymerization takes places and a polymer particle suspended in the water phase forms that is much smaller than the original monomer droplet (see Figure 5.3.12 for a graphical illustration of these steps). At the end of the overall emulsion polymerization process, all monomer droplets have been consumed by the polymerization reaction in the micelles. Typical emulsifiers for emulsion polymerization are natural or synthetic detergents, such as, for example, sodium palmitate or sodium alkyl sulfonates. Emulsion polymerization is very versatile and is applied for many polymers [e.g., PVC, styrene copolymers, poly(methacryl esters)] in batch, semi-continuous, and continuous processes. In some cases, the obtained polymer particles in water are directly applied as technical products for coatings, lacquer applications, or as adhesives. In other cases the formed product is further treated to obtain the dry polymer. Note that the aqueous phase in emulsion polymerization always contains some isolated emulsifier and also some monomer. Moreover, the formed polymer contains the emulsifier as impurity. 

In the latter part of stage 1, the cement particles in the paste become fiilly coated with a layer of hydrate products. This protective layer hinders the diffusion of the reacting species in and out of the reaction interphase, thus sharply reducing the rate of the various reactions. The system enters into a period of latency referred to as the induction or dormant period processes initiated during stage I, however, will continue throughout the induction period. 

A membrane of thickness, L, is covered by an infinitely thin, impermeable surface film with cracks (5,6). A symmetry unit of a single repeat in the lattice is shown in Figure 6A. The length of the symmetry unit is b and the length of a continuous portion of the impermeable surface coating is 2q (Figure 6B). Within the membrane, Laplace s equation describes the steady state diffusion process,... 

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