Localization and quantification of radical production in cavitating flows with luminol chemiluminescent reactions.

Hydrodynamic cavitation experiments in microfluidic systems have been performed with an aqueous solution of luminol as the working fluid. In order to identify where and how much reactive radical species are formed by the violent bubble collapse, the resulting chemiluminescent oxidation reaction of luminol was scrutinized downstream of a constriction in the microchannel. An original method was developed in order to map the intensity of chemiluminescence emitted from the micro-flow, allowing us to localize the region where radicals are produced.

Comparative study of luminescence and chemiluminescence in hydrodynamic cavitating flows and quantitative determination of hydroxyl radicals production.

Luminescence and chemiluminescence have been experimentally investigated in hydrodynamic cavitating flows. By using dedicated microdevices inserted inside a light tight box, photons counting has been made possible. Luminescence has been investigated with deionized water as the working fluid; chemiluminescence has resulted from cavitating alkaline luminol solutions, and has been correlated to hydroxyl radicals formation.

Liquid-phase exfoliation of graphite into graphene nanosheets in a hydrocavitating 'lab-on-a-chip'.

Hydrodynamic cavitation 'on a chip' has been used to achieve liquid-phase exfoliation of natural graphite to get graphene. We have taken advantage of the small size of such a 'lab-on-a-chip' (LOC) with low input-power consumption, to produce afterwards few layers of graphene nanosheets in a surfactant suspension. Characterization of the processed material has been performed by TGA analysis, SEM, TEM, AFM and Raman measurements.

Observation of chemiluminescence induced by hydrodynamic cavitation in microchannels.

We have performed hydrodynamic cavitation experiments with an aqueous luminol solution as the working fluid. Light emission, together with the high frequency noise which characterizes cavitation, was emitted by the two-phase flow, whereas no light emission from luminol was recorded in the single phase liquid flow. Light emission occurs downstream transparent microdiaphragms.

Experimental evidence of temperature gradients in cavitating microflows seeded with thermosensitive nanoprobes.

Thermosensitive fluorescent nanoparticles seeded in deionized water combined with confocal microscopy enables thermal mapping over three dimensions of the liquid phase flowing through a microchannel interrupted by a microdiaphragm. This experiment reveals the presence of a strong thermal gradient up to ~10(5) K/m only when hydrodynamic cavitation is present. Here hydrodynamic cavitation is the consequence of high shear rates downstream in the diaphragm.

Structure and rheology of SiO2 nanoparticle suspensions under very high shear rates.

High shear rate experiments have been performed with capillary microviscometers onto SiO2 nanoparticles dispersed in alcohol (so-called nanofluids). The aim of these experiments was to investigate the processes of aggregation and dislocation of the nanoparticles in a shear flow under perikinetic and orthokinetic conditions. Shear rates as high as 2x10(5) s-1 were obtained in pressure-driven microchannels laminar flows.

Microfluidic on chip viscometers.

We present the design and the process of fabrication of micromachined capillary on chip rheometers which have performed wall shear stress and shear rate measurements on silicon oil and ethanol-based nanofluids. The originality of these devices comes from the fact that local pressure drop measurements are performed inside the microchannels. Thus, the advantage over existing microviscometers is that they can be used with the fluid under test alone; no reference fluid nor posttreatment of the data are needed.