Film-air interface

In writing the energy balance (Equation 5.17) we slipped another fast one by the reader by assuming h to be the same as ho, the heat transfer coefficient from the liquid film-air film interface to the air. If a significant resistance is associated with the liquid film, h is better expressed by the overall heat transfer coefficient (U), which consists of both he andhL. Note that hL is the convection coefficient from the liquid film to the interface [7], When appreciable liquid film resistance exists, our energy balance should be written as... 

According to the geometrical optics treatment (Bom and Wolf, 1980), the angular dependence of reflectance p,2 at the air/film interface for 5- andp-... 

If the refractive index of the substrate is greater than that of the film then a phase change will be introduced both at the air-film interface and at the film-substrate interface. In this case, the reflected colour seen at normal incidence when viewed in white light will be the complementary colour to that just described. These are listed in Section S4.ll in the column labelled colour transmitted . 

This effect is particularly important for photopolymerized thin films. In an open air environment, oxygen continually diffuses into the film from the air-film interface ... 

In addition to the optical path difference due to the difference in path lengths between the two rays there will be an additional path difference of A due to the additional phase difference of it that occurs at the air-film interface... 

There is no additional contribution of due to reflection at an air-film interface. The only reflections occur in the soap film medium at film-air interfaces. These reflections produce zero phase difference. The intensity of the transmitted beam. It, can be obtained from the result for reflected rays, (2.26), as the sum of Ir and /< must equal the total incident intensity, /<, if no absorption of light by the soap film takes place. Thus... 

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