Background information. Marine nematodes belonging to the Stilbonematidae (Desmodoridae) family are described as living in obligatory association with sulfur-oxidizing chemoautotrophic ectosymbionts. The symbiotic bacteria carrying out this chemosynthesis should contain elemental sulfur in periplasmic granules as sulfur granules of chemoautotrophic endosymbionts described in various marine invertebrates.Results. Based on TEM (transmission electron microscopy) analyses, extracellular bacteria surrounding Eubostrichus dianae possess these spherical periplasmic granules. Few investigative techniques can be used to identify elemental sulfur, S 8 , such as EDXS (energy dispersive X-ray spectroscopy) and EELS (electron energy loss spectroscopy), which are associated with cryo-fixation of the sample to avoid sulfur loss. These techniques are time consuming, expensive and require technical skills. Raman microspectrometry applied to the analysis of E. dianae allowed us to detect elemental sulfur, S 8 , and confirmed the location of these sulfur clusters in the bacterial coat. In the same way, Raman spectrometry was positively applied to the endosymbiotic bivalve Codakia orbicularis, suggesting that this technique can be used to characterize sulfur in ecto-as well as in endo-symbiotic sulfur-oxidizing bacteria.Conclusions. As Raman spectrometry can be used on living organisms (without preliminary fixation) without sample damage and preserving the molecular structure of the sulfur (denatured during chemical fixation), it represents a very well-adapted investigative tool for biologists. This technique therefore permits us to detect quickly and easily (in a few seconds and on entire living animals) the presence of sulfur compounds in the symbiotic nematode.
International audienceThe present work is concerned with the study of the tribological properties of various fluorinated carbon phases obtained at room temperature and then post-treated under fluorine atmosphere at different temperatures. The tribological tests evidence good intrinsic properties for all the compounds (friction coefficient in the range 0.07-0.09). Differences appear after few cycles. Friction measurements after 100 cycles and complementary Raman analyses of the tribofilm remaining in the wear scar point out that long term tribologic properties of the fluorinated compounds strongly depend on the evolution undergone by the materials under friction. The release of HF molecules, the loss of fluorine and partial rebuilding of graphitic phases are at the origin of the degradation of the friction properties. The good properties of the compounds post-treated at temperature in the range 150-300 °C are attributed to the chemical and structural stability of these compounds under friction
This work is concerned with the study of the tribological properties of fluorinated carbon nanofibres with various fluorination rates. The tribological tests, carried out in the presence of pentane and in air after liquid's evaporation demonstrate good friction properties for all the compounds (the friction coefficients ranging between 0.04 and 0.06 in the presence of pentane and between 0.07 and 0.09 in air). Raman analyses reveal that the friction process induces a partial deterioration of the carbon fibres and SEM studies show that the tribofilm is composed of individual fibres embedded in a more disordered carbonaceous matrix. The fibrous nature of the tribofilm and the experimental relationship between friction coefficient and fluorination rate strongly support that friction properties of fluorinated carbon nanofibres are governed by surface fibres interaction. The modification of the nanofibres surface tension by action of pentane or optimum fluorination rate leads to a lowering of interfibres interactions resulting in an improvement of the friction properties.
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