Browsing by Author "Wackerbarth, Hainer"

The local fuel concentration at the ignition position is a crucial parameter, especially for spark ignited engines. Hydrocarbon concentration can be determined by infrared transmission measurements because of the attenuation of infrared radiation in the 2940 cm(-1) frequency range due to the excitation of fundamental CH-stretch vibrations of the molecules. In-cylinder measurements can be done by modified spark plugs with integrated absorption paths. A tungsten halide lamp was used in the experiments as an infrared light source. There is a non-linear relation between measured transmissions and hydrocarbon densities. So far, infrared transmission measurements have to be calibrated on absolute density values by using various hydrocarbon test gases with different concentrations. Furthermore in-cylinder transmission measurements can be calibrated at homogeneous engine operation conditions. In this case, a well mixed air/fuel composition is expected at the end of the compression stroke. Both time-consuming calibration processes lead to a new calibration procedure for band integrated transmission measurements which is presented in this study. The non-linear correlations between band integrated transmissions and absorber densities were calculated by using the absorption cross section as a spectral characteristic of absorbing molecules and the filter transmission as the spectral influence of the experimental setup. The differences between measurement and calculation can be corrected by a single measurement using a test gas with known hydrocarbon concentration. The calibration procedure was verified on temperature and pressure influences by measurements using a heatable optical cell at pressures up to 1800 kPa and within a temperature range from 298 to 473 K. Finally, the calibration procedure was adapted from cell measurements to an infrared fiber optical sensor which was used for in-cylinder measurements. An adapter for the spark plug bore enables a parallel use of a flame-ionization-detector and the optical sensor. Simultaneous propane concentration measurements were made in a motored engine with both measurement systems. (C) 2010 Elsevier Ltd. All rights reserved.

Functional foods represent an emerging market of growing economic importance. The formulation of carotene fortified food emulsions involves the difficulty to transfer the carotenoids into the lipid phase. Usually, undesirable organic solvents are used to dissolve the carotenoid in the lipid phase, in particular astaxanthin and beta-carotene. Here, we present a novel approach in which the carotenoid is first bound to bovine serum albumin (BSA) and then the carotenoid-protein complex is used to prepare an emulsion. Absorbance spectroscopy indicates the formation of the complex in the aqueous phase and provides first results of the carotenoid load, which is supported by the colour of the cream phase. The droplets in the emulsion are visualized by confocal laser scanning spectroscopy, indicating the protein layer. The laser diffraction spectroscopy and confocal laser scanning spectroscopy provide the particle size distribution and insight of the stability of emulsion interface. (C) 2009 Elsevier Ltd. All rights reserved

A challenge in the detection of explosives is the differentiation between explosives and contaminants. Synthetic musk-containing perfumes can cause false alarms, as these perfumes are nitroaromatic compounds, which can be mistaken for trinitro toluene (TNT) by some detectors. We present a detection principle based on surface-enhanced Raman scattering (SERS). A stream of the airborne compounds is focused and resublimated on a cooled nanostructured gold surface. We recorded high-resolution SERS spectra of TNT, musk xylene, and musk ketone. The nitroaromatic compounds can be identified unambiguously by their SERS spectra. Even the dominant bands containing nitro-group scissoring and symmetric stretching modes are significantly shifted by the difference in molecular structure. (C) 2010 Optical Society of America

A lot of production processes involve mixing steps. The understanding of fluid flows in mixing processes of liquid components is needed in order to develop appropriate mixers for the chemical and pharmaceutical industry. Especially mixing in microfluidic systems is a challenge due to the diffusion-based processes. A multi-lamination micromixer with chessboard outlet geometry is used to induce the mixing process. To get comprehensive information about the mixing process, the velocity profile of the fluid flow and the species concentration distribution during the mixing process should be measured. Thus, we have combined particle image velocimetry (PIV) and Raman scattering. To enable rapid detection, the Raman imaging mode is used to visualise the concentration distribution. By this setup light sheets along and orthogonal to the outlet of the micromixer are recorded and synchronized with PIV measurement. As a model system we have used water and ethanol/methanol, enabling a selective monitoring of the substances by choosing appropriate spectral areas. The PIV is recorded based on Mie scattering and fluorescence using microsphere tracers. In this study, we present a setup for determination of the velocity profile field and the spatial concentration distribution of water and ethanol/methanol in a micromixer.

In this study we present a device based on surface-enhanced Raman scattering (SERS) for the detection of airborne explosives. The explosives are resublimated on a cooled nanostructured gold substrate. The explosives trinitrotoluene (TNT) and triacetone triperoxide (TATP) are used. The SERS spectrum of the explosives is analyzed. Thus, TNT is deposited from an acetonitrile solution on the gold substrate. In the case of TATP, first the bulk TATP Raman spectrum was recorded and compared with the SERS spectrum, generated by deposition out of the gas phase. The frequencies of the SERS spectrum are hardly shifted compared to the spectrum of bulk TATP. The influence of the nanostructured gold substrate temperature on the signals of TATP was studied. A decrease in temperature up to 200 K increased the intensities of the TATP bands in the SERS spectrum; below 200 K, the TATP fingerprint disappeared. (C) 2010 Optical Society of America

Incorrect medication administration causes millions of undesirable complications worldwide every year. The problem is severe and there are many control systems in the market, yet the exact molecular composition of the solution is not monitored. Here, we propose an alarm sensor based on UV-Vis spectroscopy and refractometry. Both methods are non-invasive and non-destructive as they utilize visible light for the analysis. Moreover, they can be used for on-site or point-of-care diagnosis. UV-Vis-spectrometer detect the absorption of light caused by an electronic transition in an atom or molecule. In contrast a refractometer measures the extent of light refraction as part of a refractive index of transparent substances. Both methods can be used for quantification of dissolved analytes in transparent substances. We show that a sensor combining both methods is capable to discern most standard medications that are used in intensive care medicine. Furthermore, an integration of the alarm sensor in already existing monitoring systems is possible.

The fabrication of SERS-active substrates, which offer high enhancement factors as well as spatially homogeneous distribution of the enhancement, plays an important role in the expansion of surface-enhanced Raman scattering (SERS) spectroscopy to a powerful, quantitative, and noninvasive measurement technique for analytical applications. In this paper, a novel method for the fabrication of SERS-active substrates by laser treatment of 20, 40, and 60 nm thick gold and of 40 nm thick silver films supported on quartz glass is presented. Single 308 nm UV-laser pulses were applied to melt the thin gold and silver films. During the cooling process of the noble metal, particles were formed. The particle size and density were imaged by atomic force microscopy. By varying the (Thence, the size of the particles can be controlled. The enhancement factors of the nanostructures were determined by recording self-assembled monolayers of benzenethiol. The intensity of the SERS signal from benzenethiol is correlated to the mean particle size and thus to the fluence. Enhancement factors up to 10(6) with a high reproducibility were reached. Finally we have analyzed the temperature dependence of the SERS effect by recording the intensity of benzenethiol vibrations from 300 to 120 K. The temperature dependence of the SERS effect is discussed with regard to the metal properties.

Free-flow electrophoresis techniques have been applied for separations in various areas of chemistry and biochemistry. Here we focus on the generation of a free-flow electrophoresis chip and direct monitoring of the separation of different molecules in the separation bed of the miniaturized chip. We demonstrate a fast and efficient way to generate a low-cost micro-free-flow electrophoresis (mu FFE) chip with a filling capacity of 9.5 mu L based on a multi-lamination technique. Separating webs realized by two transfer-adhesive tapes avoid the problem of gas bubbles entering the separation area. The chip is characterized by isoelectric focusing markers (IEF markers). The functionality of the chip is demonstrated by free-flow isoelectric focusing (FFIEF) of the proteins BSA (bovine serum albumin) and avidin and a single-stranded DNA (ssDNA) fragment in the pH range 3 to 10. The separation voltage ranges between 167 V cm(-1) and 422 V cm(-1), depending on the application.

Au nanostructures of different types are widely employed as substrates for surface-enhanced Raman spectroscopy (SERS) due to their strong plasmon-related near-field enhancement in the visible and NIR frequency range as well as their potential for biologically active interfaces. We report on a fabrication route for highly periodic Au nano-discs by combination of laser interference lithography (LIL) with nanoimprint lithography (NIL) using a double-layer lift-off process to produce extremely homogenous periodic arrays over areas of 6 '' wafer scale with sufficiently sharp plasmonic resonance. FDTD simulations were done to yield specifically designed plasmonic activity at a wavelength of 785 nm commonly used in Raman spectrometers. Optical characterisation of the resulting samples was compared to simulation predictions and linked to SERS signal intensity and reproducibility. (C) 2017 Elsevier B.V. All rights reserved.

Micro structured components for process engineering have gained increasing importance in chemical, pharmaceutical and life sciences applications. Understanding of mixing processes in those devices is of fundamental interest for their performance. Raman imaging with light sheets is a powerful tool to visualize concentration profiles. For the first time planar Raman imaging is combined with computational fluid dynamic (CFD) calculations to analyze the concentration of two components at the outlet of a micro mixer. The mixing process was monitored within an attached quartz cuvette. The laser light sheet had a thickness of 0.5 mm and a width of 10 mm matching the inner width of the cuvette. In this investigation ethanol and water were mixed. We present measured concentration maps within 10 mm x 10 mm using single shot laser pulses (6 ns). The lateral resolution is only determined by the pixel size of the CCD camera. Standard deviations and averaged data of the concentration profiles are compared with CFD calculations. The computations were done for a laminar flow at constant temperature under non-steady-state conditions. (C) 2011 Elsevier B.V. All rights reserved.

This study presents a method for concentration measurements of carbon dioxide and gaseous water. CO2 and H2O are infrared active substances with strong overlapping absorption bands in the spectral range at about 3700 cm(-1) due to the excitation of molecule vibrations. The analysis is based on the HITEMP database which was used to quantify spectral integrated transmission measurements. A fiber optical spark plug sensor with an absorption path close to the electrodes was used for in-cylinder measurements of carbon dioxide and gaseous water. The sensor system consists of a tungsten halide lamp as a broadband source and two infrared detectors with different optical bandpass filters. The developed calibration procedure was evaluated by using a heatable optical cell. Various gas compositions were analyzed at pressures up to 1800 kPa within a temperature range from 298 to 573 K under well defined conditions. Finally, the calibration procedure was adapted for in situ measurements of CO2 and H2O concentrations in the cylinder of a spark ignited (SI) engine. Concentrations were measured time resolved for motored as well as fired engine conditions. (C) 2013 Elsevier Ltd. All rights reserved.

A series of self-assembled coordination cages [pd(4)L(8)(n)] based on a phenothiazine backbone has been investigated by means of Raman spectroscopy in solution and by Surface Enhanced Raman Scattering (SERS) on a nanostructured Au surface. The experiments demonstrate that the cages can be clearly distinguished from their constituting ligands by their Raman spectroscopic signatures. Furthermore, the structural integrity of the interpenetrated coordination cages upon deposition on the Au surface was demonstrated for the first time. The signal assignment of the experimental vibrational spectra was supported by Density Functional Theory (DFT) calculations on suitable molecular models.

Transmittance spectra of four gaseous hydrocarbons were measured by using a Fourier transform infrared spectrometer. The analyzed substances are propane, n-butane, ethanol, and iso-octane (2,2,4-trimethyl-pentane). Mixtures of hydrocarbons and nitrogen were prepared and analyzed in an optical cell between 298 and 473 K at pressures up to 1800 kPa. Molecule specific absorption cross sections were calculated for different temperatures and pressures that are relevant for technical absorption measurements. Dependences of the spectral absorption cross sections, as well as the integrated absorption cross sections on temperature and pressure, were investigated. (C) 2010 Optical Society of America

Nanotechnology enables the generation and characterization of novel surface-enhanced Raman scattering (SERS) substrates. In this study, we focus on the impact of the carrier material of the SERS active layer and hence the dielectric environment to the enhancement. Therefore, a self-assembled monolayer of 4-nitrothiophenol is immobilized on silver and gold particles substrates on a quartz carrier. The detection of the monolayer occurs through the quartz carrier and through air. For the former, an increase of the intensity of the SERS bands in the spectrum is observed compared to the latter. The magnitude of the increase is larger for gold than for silver. Calculations according to the theoretical model of the electromagnetic enhancement agree with our experimental data. The presented detection mode will stimulate the fabrication of novel SERS sensors. Copyright (c) 2013 John Wiley & Sons, Ltd.