Although the primary objective of these studies was to investigate stratification processes in multicomponent coatings, such as butyl acrylate/polyurethane (BA/PUR) (© 1999 by Air Products and Chemicals, Inc.) latex, other objectives include investigation of step-scan photoacoustic (SS-PA) Fourier transform infrared (FT-IR) spectroscopy depth profiling capability for analysis of multicomponent systems. These studies show that a combination of step-scan photoacoustic and attenuated total reflectance (ATR) FT-IR spectroscopy can be successfully utilized to elucidate stratification processes in BA/PUR latex as well as in other multicomponent systems. ATR FT-IR experiments revealed the absence of PUR moieties within the first 0.28 mu m from the film/air (F-A) interface, a decrease of the BA component, and the appearance of PUR from 0.39 to 2.52 mu m. Coalescence of BA/PUR latex at 149 °C affects the distribution of these components by driving PUR deeper into the bulk and BA closer to the surface. SS-PA FT-IR experiments allowed us to monitor stratification processes at greater depths, and in conjunction with phase rotation analysis, show that the BA component stratifies closer to the F-A interface, whereas PUR migrates towards the film/ substrate (F-S) interface.
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