Fluorescent melamine-formaldehyde/polyamine coatings for microcapsules enabling their tracking in composites.

This study aimed the development of fluorescent melamine-formaldehyde (MF)/polyamine coatings for labelling of prefabricated microcapsules and their tracking in composites. The composition of the fluorescent MF coatings was studied by FTIR spectroscopy, thermogravimetric analysis, and elemental analysis. The characteristics of the coatings and its deposition on different surfaces were investigated using optical and fluorescence microscopy and fluorescence spectroscopy. MF prepolymers were polymerised with tri- and polyamines yielding in fluorescent coatings without addition of fluorescent dyes. Both, MF/poly(ethylene imine) and MF/poly(vinyl amine) (PVAm) coated glass beads showed maximum fluorescence at an excitation wavelength of λmax = 360 nm with the emission maxima at λmax = 490 nm and λmax = 410 nm, correspondingly. The MF/PVAm polymer was coated on diuron-poly(methyl methacrylate) microcapsules and tracked in highly filled composites (water-based plaster/paint) to show its applicability. MF/polyamine coatings were identified as promising materials for the fluorescent labelling of prefabricated microcapsules.

Detection of ammonia by photoacoustic spectroscopy with semiconductor lasers.

Sensitive photoacoustic detection of ammonia with near-infrared diode lasers (1.53 microns) and a novel differential acoustic resonator is described; a sensitivity of 0.2 parts per million volume (signal-to-noise ratio = 1) is attained. To eliminate adsorption-desorption processes of the polar NH3 molecules, a relatively high gas flow of 300 SCCM was used for the ammonia-nitrogen mixture. The results are compared with recent ammonia measurements with a NIR diode and absorption spectroscopy used for detection and photoacoustic experiments performed with an infrared quantum-cascade laser. The performance of the much simpler and more compact setup introduced here was comparable with these previous state-of-the-art measurements.

Photoacoustic measurement of methane concentrations with a compact pulsed optical parametric oscillator.

A pulsed periodically poled lithium niobate optical parametric oscillator operating in a cavity with a grazing-incidence grating configuration was used for sensitive and precise measurement of trace quantities of methane in nitrogen by photoacoustic spectroscopy with a novel differential photoacoustic detector. A sensitivity of 1.2 parts in 10(9) by volume of methane was obtained in direct calibration measurements (not extrapolated). With this apparatus, in situ measurement of the methane concentration in ambient air under atmospheric conditions was demonstrated.