Par rapport à un fluide Newtonien, les suspensions denses de particules présentent des propriétés rhéologiques différentes. Des comportements rhéofluidifiants ou rhéoépaississants liés à des phénomènes de migration de particules peuvent apparaitre. Pour des suspensions, le taux de cisaillement, la concentration et la taille des particules ont une grande influence sur ce comportement rhéologique (Denn et Morris 2014). Pour observer l'influence de ces facteurs, l'un des meilleurs moyens est de disposer d’un système simple dans lequel tous les facteurs mentionnés ci-dessus sont bien contrôlés. Ceci peut être réalisé par le développement d'une plate-forme expérimentale, sur laquelle les comportements d'écoulement de suspension (profil de vitesse et concentration locale de particules) à des vitesses de cisaillement et des concentrations de particules bien contrôlées peuvent être étudiés. Dans l'étude actuelle, 4 tâches ont été réalisées :1) Le développement d'une nouvelle formulation pour la préparation d’une suspension adaptée en indice de réfraction et en densité basée sur des particules de PMMA. 2) Le développement d'un dispositif expérimental consacré à l'étude des flux de suspension dense sous une large gamme de taux de cisaillement constant. 3) La caractérisation des profils de vitesse des flux de suspension dense sous un dispositif cône-plan utilisant des techniques de micro-PIV. 4) Une mesure préliminaire de la concentration locale de particules de la suspension sous écoulement cône-plan en utilisant des méthodes de traitement d'image. / Compared to general Newtonian fluids, highly concentrated mixtures of particles and fluid, so called dense suspensions, have different rheological properties and fluid dynamic behaviors. Such as, shear-thinning or shear-thickening effect, and apparent slip and particle migration behaviors under certain shear flow conditions. These properties are related to the application of suspension flow in real systems, for example, the blood.For suspensions, shear rate, particle concentration and particle size have a big influence of on their rheological behaviors (Denn and Morris 2014). To observe the influence of these factors, one of the best ways is to start the research from a simple case in which all the above mentioned factors are well controlled. This can be realized by developing such an experimental platform, on which the suspension flow behaviors (velocity profile and local particle concentration) at different shear rates and particle concentrations can be investigated.In the current study, 4 tasks were achieved:1) The development of a new recipe for the preparation of density and refractive index matched suspension with PMMA particles. 2) The development of an experimental set-up devoted to the investigation of dense suspension flow under a large range of constant shear rate. 3) The characterization of the velocity profiles of dense suspension flows under a cone-plate device by using micro-PIV techniques.4) A preliminary measurement of the local particle concentration of the suspension flow by using image processing techniques.

The condition of no relative velocity of fluid past solid is termed as ‘no-slip boundary condition’. This condition is a general observation in fluid mechanics. However, several research groups have recently reported slip of water for surfaces with water repelling chemistry (referred to as hydrophobic surfaces). The effect has been attributed to disruption of H-bonding network of water molecules at such surfaces and resulting nucleation of dissolved gases and even reduced water density locally in absence of dissolved air. Slip of water on hydrophobic surfaces has been demonstrated to get amplified by high degree of roughness and patterning. Trapping of air in the surface asperities has been cited as the possible reason. The present work focuses on the study of effect of surface chemistry and roughness on flow behavior close to solid surfaces. Superhydrophobic surfaces have been generated by novel methods and wet-etching has been used to generate well-defined patterns on silicon surfaces. For flow characterisation, a micrometre resolution Particle Image Velocimetry (micro-PIV) facility has been developed and flow measurements have been carried out with a spatial resolution of less than 4 µm. It has been found from the experiments that flow of water on smooth surfaces, with or without chemical modification, conforms to the no-slip within the resolution limits of experiments. Deviation is observed in case of rough and patterned hydrophobic surfaces, possibly because of trapped air in asperities. Total Internal Reflection experiments, used to visualise the air pockets, confirmed the trapping of air at asperities. Diffusion of air out of the crevices seems to be the limiting factor for the utility of these surfaces in under-water applications.