Stratification of butyl acrylate/polyurethane (BA/PUR) latexes: ATR and step-scan photoacoustic studies

Although the primary objective of these studies was to investigate stratifi cation processes in multicomponent coatings, such as butyl acrylate/polyure thane (BA/PUR) ((C) 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 ana lysis of multicomponent systems. These studies show that a combination of s tep-scan photoacoustic and attenuated total reflectance (ATR) FT-IR spectro scopy can be successfully utilized to elucidate stratification processes in BA/PUR latex as well as in other multicomponent systems. ATR FT-IR experim ents revealed the absence of PUR moieties within the first 0.28 mu m from t he film/air (F-A) interface, a decrease of the BA component, and the appear ance of PUR from 0.39 to 2.52 mu m. Coalescence of BA/PUR latex at 149 degr ees C affects the distribution of these components by driving PUR deeper in to the bulk and BA closer to the surface. SS-PA FT-IR experiments allowed u s 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.