Impingers three stage

The three-stage glass impinger developed by May is intended to correspond with the three deposition sites of the human respiratory system (Figure 13.5). The top stage corresponds to the upper respiratory tract, the middle stage to the bronchioles and the bottom stage to the alveoli. The... 

Figure 13.5 May three-stage liquid impinger (two cross-sectional views).

In all three described setups, deposition on the inserts was 50% or less of the amount usually anticipated on an equal sized area without cell culture inserts. This difference may be explained by the changed distance between orifice plate and impaction surface in the cell culture insert. The collection efficacy of an impactor/impinger decreases with an increase in the ratio of the orifice plate to impaction plate distance over jet width. Observations indicate that although the inserts are not at an optimal distance from the orifice plate and are not exactly at the same position compared to the original collection stage, the cell culture inserts do function as an impaction surface for particles in a relevant size range. 

The reactant species impinging from the vapor phase is attracted to the surface of the substrate mainly due to the instantaneous dipole moment of the substrate surface atoms. Adsorption of the condensed species is accompanied by lateral diffusion, i.e., the species moves along the surface of the substrate for a particular distance before it resides on the surface. An aggregate of condensed reactant species that reside on the surface of the substrate is termed a "nucleus". This could vary from a single atom or molecule to a cluster of species, and the process is referred to as nucleation. Nuclei are usually three dimensional island type structures formed on the surface of the substrate and nucleation is usually the initial stage of the film formation. It is worthwhile to note that, while simple condensation is usually exothermic, CVD adsorption and subsequent film formation is usually an endothermic reaction with few exceptions. 

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