Study of the dynamics of microfluidic crystals

Studies of interfaces at the nanoscale present several challenging factors, and experiments on this topic require complex instruments and setups that are not easily accessible to most laboratories. The characteristic observables, both in spatial and temporal terms, are difficult to measure accurately. Therefore, if it were possible to study theoretical models through an experimental platform operating at a larger scale, this would open new possibilities for research in the field, allowing relatively simple experimental studies to draw an analogy with the nanoscale system. It is thus first necessary to verify if this analogy can indeed be drawn and to what extent. The work carried out in this thesis is part of a broader research project that seeks to evaluate whether, and in what form, the phenomenon of superlubricity, discussed in nanotribology and first experimentally observed between two graphite sheets, can present itself in a system at a scale accessible to optical microscopy, such as the one constituted by a two-dimensional microfluidic crystal confined in a Hele-Shaw cell. The fundamental idea is that the droplets forming the crystalline lattice can interact with a periodic potential similarly to the way atomic crystals interact through the Bloch function. Hereafter, this potential that gives rise to the attractive force between the two components is modeled, using microfabrication techniques, as a well that allows the confined droplet to partially decrease its surface energy. First, the interaction of the single droplet with one of these geometric traps will be studied and characterized quantitatively. A simple model that outlines the acting forces will be developed in this thesis and compared with the experimental results. Subsequently, attention will be given to a methodical study of the realization of the microfluidic crystal, evaluating its lattice constant and purity, estimating the frictional and inertial forces that this system undergoes. The microfluidics of droplets in a closed channel is still a very open branch of physics, whose technological implications are being explored by an increasing number of research groups. In this thriving environment, enriched every year by groundbreaking publications, this study aims to contribute by offering a hint of further novelty and originality.