A quantitative determination of the polymerization of benzoxazine thin coatings by time-of-flight secondary ion mass spectrometry

Phenol-paraphenylenediamine (P-pPDA) benzoxazines exhibit excellent barrier properties, adequate to protect aluminum alloys from corrosion, and constitute interesting candidates to replace chromate-containing coatings in the aeronautical industry. For the successful application of P-pPDA coatings, it is necessary to decrease the curing temperature to avoid the delamination of the coating while preserving the mechanical properties of the alloy, as well as the barrier properties of the coating. However, decreasing the curing temperature leads to less polymerized films, the extent of which requires a quantitative assessment. While the conversion rate of the polymerization reaction is commonly evaluated for bulk samples using differential scanning calorimetry (DSC), a tool for its evaluation in thin films is missing. Therefore, a new approach was developed for that matter using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The relation between the SIMS data integrated from inside thin films and the DSC results obtained on bulk samples with the same curing cycle allowed to calibrate the SIMS data. With this preliminary calibration of the technique, the polymerization of P-pPDA coatings can be locally determined, at the surface and along the depth of the coating, using dual-beam depth profiling with large argon cluster beam sputtering.     

Fiber-optic pH detection in small volumes of biosamples

Determining the pH values of microscopic plant samples may help to explain complex processes in plants, so it is an area of interest to botanists. Fiber-optic probes with small dimensions can be used for this purpose. This paper deals with the fiber-optic detection of the pH values of droplets of plant xylem exudate based on ratiometric fluorescence intensity measurements with an internal reference. For this purpose, novel V-taper sensing probes with a minimum diameter of around 8 μm were prepared that enable the delivery of fluorescence signal from the detection site on the taper tip to the detector. The taper tips were coated with pH-sensitive transducer (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt; HPTS) and a reference [dichlorotris-(1,10-phenanthroline) ruthenium (II) hydrate (Ru-phen dichloride)] immobilized in a xerogel layer of propyltriethoxysilane and (3-glycidoxy)propyl trimethoxysilane. The prepared probes were sensitive to pH values mainly in the range from 6.0 to 9.0. In the pH range 6–9, the results were limited by measurement errors of about 0.2 pH units, and in the pH range 5–6 by measurement errors of about 0.5 pH units. Using the developed V-taper sensing probes, the pH values of in vivo and in vitro samples of small volumes (∼6 μl) of exudate were measured. The results were validated by comparison with conventional electrochemical pH measurements.     

Effect of Doping Silica Gel Layers with TiOTi-Chains and Cu2+-Ephedrine on the Sensitivity of the Layers to Gases

In this paper the interaction of polysiloxane and TiOTi-doped polysiloxane gel layers containing Cu²⁺-ephedrine (CuEP) with carbon dioxide, nitrogen and water is investigated. This interaction is studied through changes of the output optical power from an optical fiber coated with the investigated gel layer. The layers are prepared with sols based on tetraethoxysilane and titanium isopropoxide, isopropanol, acetylacetone and Cu²⁺-ephedrine by the repeated dip-coating method. The applied gel layers are dried at 70°C.Spectral and temporal changes of the output optical power due to effect of the tested gases are measured. The measurements show big changes of the output optical power of fibers coated with CuEP-doped silica gel layers in a wavelength range from 400 to 700 nm, which is in relation with spectral effects of CuEP in alcoholic solutions. Relatively lower changes of the attenuation spectra without any attenuation band are found in the spectra of TiOTi-doped siloxane gel layers containing CuEP. The angular distributions of the output optical power of the coated fibers indicate high optical losses of the layers.