This report presents how combination of internal reflection (IR) and infrared imaging (IRI) can reach a surface spatial resolution at 1000 nm levels in the middle infrared range. As a result, vibrational spectra from these size areas can be recorded at high signal-to-noise levels. A spatial calibration of this method was performed by correlating IRIRI data with SEM micrographs and optical images of geometrically well-defined polymeric photoresists as well as Nylon fibers imbedded into a polyester matrix. The IRIRI approach has the potential of obtaining even better surface spatial resolution of vibrational spectra when internal reflection elements with greater refractive index ratios in the middle IR range become available.
Film formation of waterborne two-component polyurethanes is exceedingly complex due to the heterogeneous nature along with simultaneous progression of several parallel physicochemical processes which include water evaporation, cross-linking reactions, phase separation, and droplet coalescence, to name a few. While internal reflection infrared imaging (IRIRI) spectroscopy clearly facilitates analysis of chemical changes resulting from film formation, the complexity of processes leading to formation of specific surface/interfacial entities is a major experimental challenge. For this reason, we combined a spectrum of surface/interfacial analytical approaches including IRIRI, atomic force microscopy, and attenuated total reflectance Fourier transform infrared spectroscopy with Monte Carlo computer simulations to advance the limited knowledge of how temperature, stoichiometry, concentration levels, and reactivities of individual components affect the development of surface morphologies and compositional gradients across the film thickness. These studies show that in heterogeneous systems having both hydrophobic and hydrophilic components stratification of individual components to the film-air (F-A) interface is ultimately responsible for formation of rough surface topographies. These studies show that simultaneous stratification of hydrophobic components along with water evaporation to the F-A interface results in metastable interfacial layers, leading to surface dewetting. Subsequently, surface roughness is enhanced by higher concentrations of water in the cross-linking film.
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