Changes in the chemical composition of the Langmuir film, including:
Changes in the molecular orientation in the Langmuir film, including:
KSV NIMA PM-IRRAS is a state-of-the-art compact Fourier Transform IR-spectrometer. By positioning the spectrometer and detector on a goniometer above the surface the experimental setup is greatly simplified and provides results within minutes instead of days as in traditional IRRAS systems. The open design allows combined use of other complementary equipment such as external UV light sources and heating. The instrument can be positioned above a fully equipped analytical KSV NIMA Langmuir Trough, facilitating accurate monolayer studies without restrictions.
PM-IRRAS technology allows the measurement of surface specific FT-IR spectra in materials by recording the differences in the reflection of p- and s-polarized light from interfaces enabling detection of chemical compositions and molecular orientation from interfacial films down to films one molecule thick.
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In reflectance measurement mode the instrument delivers infrared spectra from an air-water interface or IR-reflective surface. The air-liquid measurement allows observation of any changes in thin film functional groups at the interface. This can be due to structural changes caused by chemical reaction, phase transition or other phenomena. With IR-reflective samples the s-polarization disappears and allows direct access to molecular orientation of the coating. Due to the open design, polymerization reactions on solid surfaces initiated with temperature or UV- light can be easily performed.
Traditional transmittance measurements, such as the study of KBr pellets, are possible due to the flexibility of the goniometer. Measuring non-modulated polarized or non-polarized IRRAS is also possible by turning off polarization.
PM-IRRAS is an excellent method for FT-IR experiments of nanometer scale thin films. It was possible to acquire FT-IR spectrums of films of around 2 nm thick, and also deduce molecular orientation from the experiments. Linear correlation between LB layer number and peak intensities was discovered. This demonstrates that the KSV NIMA PM-IRRAS is a powerful tool for thin film characterization and analysis. The measurements are fast and simple to perform thanks to KSV NIMA PM-IRRAS unique design.
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PM-IRRAS spectra of SA Langmuir-Blodgett films of increasing thickness on gold at (A) pH 2 and (B) pH 6 in the C-H stretch region.
Polymerization kinetics were calculated for ultrathin layers of monomers by using data from PM-IRRAS measurements. In this study it was shown that the obtained kinetic data could be placed in the regular exponential growth equation of polymerization and that it was possible to obtain the activation energy for the epoxy polymerization that corresponded well with known values. The bleaching of porphyrin can also be monitored with the method and it was shown that a polymerized layer bleached slower than a polymerized one.
|Increase of the 1700-1800 cm-1 bands during UV bleaching of TAEP film.||PM-IRRAS spectra of unpolymerized TAEP film as a function of time.|