The research presented in this thesis focusses on the experimental study of two fundamental questions: the crystal-to-glass transition and how aggregates of adhesive droplets spread on a surface. Aggregates made of lightly adhesive oil droplets are used as models for crystals or amorphous glasses. The force applied on the aggregates can be directly measured as they are compressed. A large portion of the work focusses on the crystal-to-glass transition and tries to answer the following question: how many defects are needed in a crystal for its mechanical response to be like a glass? To answer this question, the mechanical response of a perfect mono-crystal is measured. It is found that crystals deform elastically until they fail catastrophically in a single event once the force exceeds a critical value: the yield stress. The force measured during the compression of a crystal shows a well defined number of peaks which only depends on the initial geometry of the aggregate. As defects are added (the amount of disorder increased) the number of peaks in the force measurement increases rapidly before it saturates at a value obtained for model glasses. The magnitude of the force peaks also decreases as disorder is introduced. This work concludes that even a small amount of disorder in a crystal has a significant impact on its mechanical properties. In the second project, the spreading of a monodisperse aggregate of oil droplets is studied. Droplets are added one-by-one to a growing aggregate and the area covered on the interface is measured. It is found that after an initial 3D growth, the height of the aggregate saturates and the growth only happens in 2D along the horizontal direction. The growth is analogous to a puddle of liquid. In analogy with the capillary length in liquids, the ``granular capillary length" is introduced to characterize the balance between buoyancy acting on the droplets and the adhesion strength. The height of the aggregates, in the later stage of the growth, is set by this length scale. A method was developed to characterize the adhesion between two droplets, a key parameter in this experiment, as a function of the relevant experimental parameters. / Thesis / Doctor of Philosophy (PhD)

Emulsions and colloidal suspensions have various industrial applications but are also used in laboratories as model systems for studying the different phases of matter. They are versatile as their nature, size and inter-particle interactions are easily tuneable. These systems are perfect for studying questions such as the phase transition. In this thesis, we investigate the transition from an ordered crystal to a disordered glass. Perfectly ordered crystals are modeled by clusters of highly monodisperse droplets. We study the transition toward a glassy system by mixing two monodisperse populations of droplets in different proportions. The clusters are compressed between two thin glass rods, one of which is a force transducer. The forces within the clusters are directly measured and used as an indicator of the composition of the cluster. Upon introduction of disorder, the number of peaks in the force measurement increases drastically. We find that the way the energy is dissipated in the cluster is valuable information to characterize the crystal-to-glass transition. In addition to the experimental study of the crystal-to-glass transition, we have developed an analytical model that is in full agreement with the experimental observations. A crystal is modeled as an assembly of Hookean springs that will store elastic energy until it reaches a fracture point. We are able to predict the number of peaks in the force measurements when defects are introduced using simple geometric arguments. From this prediction, the way the work is dissipated in a given transition can be predicted. / Thesis / Master of Science (MSc)