The definition of granular matter is extremely broad; any collection of conglomeration of particles larger than 100 micrometers can be considered as part of this group, and virtually the entire universe is composed of them. Examples are found in many fields, e.g. in nature (dunes, avalanches, asteroids, etc.), industry (preparation of medicines, manufacture of concretes, paints, etc.), and even food (corn, wheat, etc.). As a result, its applications are very varied and numerous, and undoubtedly constitute an important focus of study for scientists. In this thesis, we attempted to understand and describe granular materials probing three distinct granular systems with an intruder. (i) In our first system, we study the impact and settling of a sphere in a suspension of cornstarch in which the suspending fluid is gradually changed from pure water to pure ethanol. We show that partly replacing water by ethanol strongly alters the suspension rheology, turning the suspension from a strongly shear-thickening fluid into its opposite: a shear-thinning liquid. We relate the macroscopic behaviour to the microscopic details of the grain-grain interaction using atomic force microscopy. (ii) In our second system, we build a rotor similar to the famous Smoluchowski-Feynman device, which is immersed in a granular gas and experimentally study the behaviour of its angular velocity distribution. We find that the existing models are not capable of adequately describing the experimentally observed distribution. However, we show that incorporating the effects of the external friction and the collision rate experienced by the rotor into models leads to full agreement with our experiments. (iii) Finally, in our third system, we study the behaviour of the granular Leidenfrost state. This is a particular state in which a denser region of grains is floating on top of a dilute one. We built a setup, which permits the observation of the granular Leidenfrost state for a wide range of parameters and more specifically allows for thorough characterization of the low-frequency oscillation that is present in this state. In this experiment, unlike the others two, we do not introduce an external object, since the intruder is generated by the system itself.
|Award date||27 Jan 2017|
|Place of Publication||Enschede|
|Publication status||Published - 27 Jan 2017|