RT Dissertation/Thesis
T1 Fluctuations and patterns in ultrathin fluid films
A1 Rodríguez-Fernández, Enrique
AB Self-organization processes, in which some form of collective behavior arises fromlocal interactions in a physical system, are promising mechanisms in the context ofmanufacturing at ultra small scales, where processing techniques are technically challenging.In many cases, the approach is to induce self-organization or self-assemblyphenomena on the system surface |which indeed acquires an increased importanceat small scales because of the enhanced surface-to-volume ratio| as a result of whicha desired surface morphology is achieved, with different properties depending on itsintended application.In this thesis, we consider two important examples of self-organization processeswhich take place at the surfaces of many small non-equilibrium systems. One of them,kinetic roughening, reflects the dominance of fluctuations in the surface morphology,with strong correlations which are quite similar to those of an equilibrium system ata continuous phase transition. The second, opposite self-organization process is theformation of ordered patterns. In the thesis, we will deal with the control of the leveland type of various surface properties, like roughness and other, and the conditionsfor the emergence of a varying degree of spatial order in patterns via spontaneousphysical processes.We work in the context of ultrathin fluid films on solid substrates, focusing on therole of the physical effects that become relevant at these very small scales -but not so much at larger scales-, while other loose their relevance. One of these aspects isthe thermal noise. The other one is the interaction between the uid surface and thesubstrate, that play a key role in the two reference physical systems we are going tostudy: an ultrathin fluid film falling down an inclined plane |where the dynamics ofthe fluid surface follows the celebrated Kuramoto-Sivashinsky (KS) equation -anda ferrofluid ultrathin film under a magnetic field.Both kinetic roughening and pattern formation usually exhibit some kinds ofuniversal behavior. The universality classes in the kinetic roughening processes thatoccur in several approximations of the KS equation are widely studied in this thesis. These universality classes are characterized by both how the fluctuations scalewith space and time and how these fluctuations are statistically distributed. Wewill deal with the emergence of symmetries in the fluctuation distributions that areunexpected considering the bare microscopic interactions; the non-trivial relationbetween the universality class of closely related models; with a novel physical mechanismthat induces the transition between different universality (sub)classes as thesystem temperature and hence the dominant nature of the fluctuations (chaotic orstochastic) changes, and finally with some anomalous kinetic roughening processes inthe limit of vanishing viscosity and surface tension. Finally, on the other hand, theformation of highly ordered patterns is assessed in the context of ultrathin ferrofluidfilms under a magnetic field, due to the spontaneous physical break-up of the filminto drops. The conditions under which higher levels of order are achieved will bedescribed. This is intended as a proof-of-concept, previous step that could encourageexperiments being performed for this type of systems.
YR 2022
FD 2022-03
LK https://hdl.handle.net/10016/35088
UL https://hdl.handle.net/10016/35088
LA eng
NO This Doctoral Thesis has been supported by Ministerio de Educación, Culturay Deporte (Spain) through Formación del Profesorado Universitario scolarship No.FPU16/06304. Additionally, research by the author has been partially supportedby Ministerio de Economía y Competitividad, Agencia Estatal de Investigación, andFondo Europeo de Desarrollo Regional (Spain and European Union) through grantNos. FIS2015-66020-C2-1-P and PGC2018-094763-B-I00.
DS e-Archivo
RD 30 abr. 2024