Imaging subsurface damage of grinded fused silica optics by confocal fluorescence microscopy

International audienceWe report an experimental investigation of fluorescence confocal microscopy as a tool to measure subsurface damage on grinded fused silica optics. Confocal fluorescence microscopy was performed with an excitation at the wavelength of 405 nm on fixed abrasive diamond grinded fused silica samples. We detail the measured fluorescence spectrums and compare them to those of oil based coolants and grinding slurries. We evidence that oil based coolant used in diamond grinding induces a fluorescence that marks the subsurface damages and eases its observation. Such residual traces might also be involved in the laser damage process

Subsurface damage measurement of ground fused silica parts by HF etching techniques

International audienceDetection and measurement of subsurface damage of ground optical surfaces are of major concern in the assessment of high damage thresholds fused silica optics for high power laser applications. We herein detail a new principle of SSD measurement based on the utilization of HF acid etching. We also review and compare different subsurface damage (SSD) characterization techniques applied to ground and fine ground fused silica samples. We demonstrate good concordance between the different measurements

150 years of foredune initiation and evolution driven by human and natural processes

International audienceForedunes are efficient natural coastal defenses acting as protective barriers during storm events. They also have the capacity to be an ecosystem hosting significant biodiversity. The economic development and/or recreational use of the foredune commonly results in a modification of natural functioning and the concomitant mixing of natural and anthropogenic processes. While the impact of human interventions on the short term evolution of coastal dunes is reasonably well understood, relatively less is known on their imprint at a scale of several decades. The Truc Vert beach-dune system (SW France), which has been exposed to various dune management strategies for more than a century, provides a relevant site to explore the respective contributions of natural and anthropogenic processes on coastal foredune evolution and the current coastal dune landscape. For this purpose, the coastal dune system was investigated using several approaches that combine ground penetrating radar (GPR), topographic data, aerial photographs and historical maps.A 20-m thick GPR sequence provides a stratigraphic record from which we detail ~150-year period of coastal dune change, including the initiation of the foredune. Results show a mixture of radar facies typical of natural aeolian erosion or deposition and radar facies that are the signature of human actions. These anthropogenic works include a large fence emplaced in 1860 to build and fix the foredune, and intense mechanical reshaping of the dune profile by bulldozers in 1972 followed by an intensive planting of vegetation. These various management strategies had a profound influence on coastal dune changes and, in turn, on the current coastal dune landscape. Historic archives documenting coastal dune works were critical to discriminate some of the radar facies, which could be wrongfully interpreted as natural erosion or deposition facies. Therefore, these results demonstrate the importance of coupling GPR and historical documentation wherever possible to determine, in part or fully, the contributions of human interventions and actions in modern dune evolution and morphological development

Impact of pNIPAM Microgel Size on Its Ability To Stabilize Pickering Emulsions

We study the influence of the particle size on the ability of poly(N-isoprolylacrylamide) microgels to stabilize direct oil-in-water Pickering emulsions. The microgel size is varied from 250 to 760 nm, the cross-linking density being kept constant. The emulsion properties strongly depend on the stabilizer size: increasing the particle size induces an evolution from dispersed drops and fluid emulsions toward strongly adhesive drops and flocculated emulsions. In order to get insight into this dependency, we study how particles adsorb at the interface and we determine the extent of their deformation. We propose a correlation between microgel ability to deform and emulsion macroscopic behavior. Indeed, as the microgels size increases, their internal structure becomes more heterogeneous and so does the polymeric interfacial layer they form. The loss of a uniform dense layer favors bridging between neighboring drops, leading to flocculated and therefore less handleable emulsions

Fundamental study of emulsions stabilized by soft and rigid particles

Two distinct uniform hybrid particles, with similar hydrodynamic diams. and comparable zeta potentials, were prepd. by copolymg. N-iso-Pr acrylamide (NIPAM) and styrene. These particles differed in their styrene to NIPAM (S/N) ratios of 1 and 8, and were referred to as S/N 1 and S/N 8. Particle S/N 1 exhibited typical behavior of soft particles, i.e., the particles shrank in bulk aq. solns. when the temp. was increased. As a result, S/N 1 particles were interfacially active. In contrast, particle S/N 8 appeared to be rigid in response to temp. changes. In this case, the particles showed negligible interfacial activity. Interfacial shear rheol. tests revealed the increased rigidity of the particle-stabilized film formed at the heptane-water interface by S/N 1 than S/N 8 particles. As a result, S/N 1 particles were shown to be better emulsion stabilizers and emulsify a larger amt. of heptane compared to S/N 8 particles. The current investigation confirmed a better performance of emulsion stabilization by soft particles (S/N 1) than by rigid particles (S/N 8), reinforcing the importance of controlling softness or deformability of particles for the purpose of stabilizing emulsions. [on SciFinder(R)