A foam is not a homogeneous material, but consists of a large number of small air bubbles. The whole is more than the sum of its parts: even though the behavior of a single bubble is easy... Show more A foam is not a homogeneous material, but consists of a large number of small air bubbles. The whole is more than the sum of its parts: even though the behavior of a single bubble is easy to understand, their collective behavior is much more complicated and completely different. The reason for this is that a deformation of the whole is only reflected partially in the deformation of individual bubbles. Instead, a large part of the deformation is reflected in a change in the structure of the foam. In this thesis, we investigate this change in structure. In the first part of this thesis, we use a simple microscopic computer model to simulate the response of a foam when it is deformed by a tiny amount, and measure how far we need to deform the foam until it is irreversibly deformed. In the second part of this thesis, we focus on an experiment, where we measure the response of a two-dimensional foam when it is deformed at the edges. We observe that the response of bubbles in the center of the foam qualitatively depends on how densely the bubbles are packed together. Show less
When soft, repulsive particles, like foam bubbles or emulsion droplets, are sheared, they show interesting scaling behaviour. We develop a simple scaling model that captures the rheological... Show moreWhen soft, repulsive particles, like foam bubbles or emulsion droplets, are sheared, they show interesting scaling behaviour. We develop a simple scaling model that captures the rheological behavior starting from three assumptions that explicitly depend on the microscopic interactions. This model starts from three ingredients: energy conservation, the concept of an effective steady state strain in our flowing system and a constitutive elasticity equation linking the effective strain to the shear stress. Our model allows for non-linear microscopic particle interactions and it predicts that the global rheological behaviour depends on the details of the microscopic interactions between the particles - in contrast to standard critical scaling theory. We test our model in computer simulations of soft, massless particles under steady shear and find that the numerics are broadly consistent with our model. jamming, rheology, foam, critical scaling Show less
