24 research outputs found
Using Polarized Spectroscopy to Investigate Order in Thin-Films of Ionic Self-Assembled Materials Based on Azo-Dyes
Three series of ionic self-assembled materials based on anionic azo-dyes and cationic benzalkonium surfactants were synthesized and thin films were prepared by spin-casting. These thin films appear isotropic when investigated with polarized optical microscopy, although they are highly anisotropic. Here, three series of homologous materials were studied to rationalize this observation. Investigating thin films of ordered molecular materials relies to a large extent on advanced experimental methods and large research infrastructure. A statement that in particular is true for thin films with nanoscopic order, where X-ray reflectometry, X-ray and neutron scattering, electron microscopy and atom force microscopy (AFM) has to be used to elucidate film morphology and the underlying molecular structure. Here, the thin films were investigated using AFM, optical microscopy and polarized absorption spectroscopy. It was shown that by using numerical method for treating the polarized absorption spectroscopy data, the molecular structure can be elucidated. Further, it was shown that polarized optical spectroscopy is a general tool that allows determination of the molecular order in thin films. Finally, it was found that full control of thermal history and rigorous control of the ionic self-assembly conditions are required to reproducibly make these materials of high nanoscopic order. Similarly, the conditions for spin-casting are shown to be determining for the overall thin film morphology, while molecular order is maintained
Salmonella-based Rodenticides and Public Health
Several countries still permit strains of Salmonella enterica serotype Enteritidis, a leading cause of gastrointestinal illness in humans, to be used in rat baits. To assess the human health risk associated with such rat bait, we first reviewed historic data on health hazards associated with Ratin, a rodenticide that was used in Europe until the early 1960s. Ratin caused outbreaks of human illness, including several deaths. We then compared S. Enteritidis isolated from a current commercial product, Biorat, with S. Enteritidis from Ratin and found that the strains were both phage type 6a. Based on the similarity of the strains, currently available Salmonella-based rodenticides likely are as great a threat to public health as historic strains were. Health officials should be aware that the continued use of Salmonella-based rodenticides is a risk to public health and should take appropriate measures to prevent use in their jurisdictions