Für die Evaluierung von Mischungsvorgängen in Mikroreaktoren ist es notwendig, diese genauer untersuchen zu können. Dazu wird ein neuartiges, optisches Messsystem vorgestellt, das die Visualisierung von mischungs‐ und diffusionslimitierten Vorgängen sowie Konzentrationsunterschieden in Fluidfilmen ermöglicht. Es besteht aus einer fokussierenden Optik mit einem Mikroskop‐Objektiv. In der Kombination mit einem Raman‐Spektrometer können so verschiedene Prozesse wie z. B. Diffusion im Mikroreaktor nicht‐invasiv gemessen und untersucht werden.
Double emulsions show great potential for encapsulating active substances and protecting them against external influences. However, they tend to become unstable during storage. Research on double emulsions, therefore, focuses on maintaining their microstructure during their shelf life. Optical measurement methods, such as Raman spectroscopy, have hardly been used to date to analyze the microstructure of double emulsions, mainly due to multiple scattering effects. This study investigates the influence of refractive index matching of double emulsion phases by measuring the Raman signal strength of the inner water phase for different refractive index combinations. Ammonium nitrate and glycerol are added to the inner and outer water phase, respectively, to change the refractive indices of both phases. Additionally, polyvinyl alcohol serves as an emulsifier in the outer water phase. The oil phase consists of silicone oil and Dowsil Resin XR 0497 as the emulsifier. The refractive index of the oil phase is kept constant. For individual phase boundaries of single droplets, the refractive index matching plays a minor role. However, if there are many droplets with correspondingly numerous phase boundaries, which leads to multiple scattering during the measurement, the matching has a significant influence on the signal strength of the inner phase. When measuring double emulsions, the phases should always be matched, as this results in higher signals and improves the sensitivity of the measurement.
Double emulsions arouse great interest in various industries due to their ability to encapsulate value-adding ingredients. However, they tend to be unstable due to their complex structure. Several measurement techniques have already been developed to study and monitor the stability of double emulsions. Especially for the measurement of the filling degree of double emulsions, so far there is no reliable method available. In this paper, a measurement system is presented that can measure the filling degree of water-in-oil-in-water (W/O/W) double emulsions by both spectrometrical and photometrical means. The method is based on the Raman effect and does not require any sample preparation, and the measurement has no negative influence on the double emulsion. It is shown that both spectrometric and photometric Raman techniques can reliably distinguish between double emulsions with filling degrees that have a 0.5% difference. Additionally, oil droplet sizes can be photometrically measured. Furthermore, the measurement system can be integrated into both inline and online emulsification processes.
In dieser Arbeit wird die Möglichkeit aufgezeigt, mithilfe einer sehr empfindlichen Einzel-Photonenmesstechnik Streulicht von Partikeln zu messen, das durch den Einsatz von Lasern mit extrem geringen Laserintensitäten erzeugt wurde. Die entstehenden Vorteile für nach diesem Prinzip zu bauende Geräte liegen im Bereich Explosionsschutz, Vermeidung von Produktschädigungen und Arbeitssicherheit. Es werden Messaufbauten zum Vermessen von Suspensionen und Aerosolen beschrieben. Laserleistungen kleiner 5 mW werden eingesetzt. Die Messungen beginnen ab einer Partikelgröße von 200 nm und werden in einer 90°-Anordnung als worst case durchgeführt, da bei diesem Winkel ein Minimum an Streuung vorliegt.This work shows the possibility to measure scattered light from particles, which are exposed to miniscule laser intensities, with the help of a very sensitive single-photon measurement technique. The advantages for subsequently designed sensors can be found in explosive prevention, avoiding product damage and improved user safety. Measurement systems to examine suspensions and aerosols are described. Laser output is less than 5 mW. The measurements start at 200 nm particle diameter and are carried out in a 90°arrangement as a worst-case scenario for scattering intensities.
Abstract. In this paper we discuss the results of an intercomparison for free space antenna factor measurements performed within the German Calibration Service (DKD). Three different types of antennas covering the frequency range from 30 MHz to 26.5 GHz have been calibrated in five different laboratories using different methods and calibration sites to obtain the free space antenna factor. The results agree well within the uncertainties specified by the laboratories suggesting that different approaches and different measurement sites to obtain the free space antenna factor are well compatible.
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