Publicação
Self-assembly of colloids driven by external fields
| Resumo: | We study self-assembly of colloidal particles under the influence of two types of external fields: one space-dependent where the system evolves into a stationary state (equilibrium) and the other time-dependent that keeps the system out of equilibrium at all times. We perform extensive Brownian dynamics simulations with different field profiles. In the first case, we analyze the formation of bands of colloidal particles driven by periodic external fields. We determine the dependence of the band width on the strength of the particle/particle interaction and on the strength and periodicity of the field. We also investigate the switching (field-on) dynamics and the relaxation times as a function of the system parameters. The observed scaling relations were analyzed using a simple dynamic density-functional theory of fluids. In the second case, we study the formation and stability of lanes under the influence of time-varying (rotating) fields. Lanes are stable kinetic structures formed in colloidal mixtures composed by opposite charged particles subjected to counterflow imposed by a uniform external field. We find that these structures resist the rotation of the field for small angles (increasing the shift between the lanes orientation and the direction of the field) but they are destroyed and rearranged into lanes along new orientations according to quantized angles (the magic angles) in a system with periodic boundary conditions. The evolution is constrained by these magic angles and has a dependence on the angular velocity of the field and its intensity. We also employ the Voronoi tessellation method to identify the clusters during the evolution and find that both the number of clusters and the distribution of the area of the Voronoi cells depend on the state of the system. When the evolution is trapped in a lane configuration the number of clusters is minimal and there is a greater number of small cells compared with the mixed state in which particles move along the field direction. |
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| Autores principais: | Nunes, André S. |
| Assunto: | Colloides Dinâmica Browniana Sistemas fora de equlíbrio Relaxação para o equlíbrio Teses de mestrado - 2015 |
| Ano: | 2015 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | We study self-assembly of colloidal particles under the influence of two types of external fields: one space-dependent where the system evolves into a stationary state (equilibrium) and the other time-dependent that keeps the system out of equilibrium at all times. We perform extensive Brownian dynamics simulations with different field profiles. In the first case, we analyze the formation of bands of colloidal particles driven by periodic external fields. We determine the dependence of the band width on the strength of the particle/particle interaction and on the strength and periodicity of the field. We also investigate the switching (field-on) dynamics and the relaxation times as a function of the system parameters. The observed scaling relations were analyzed using a simple dynamic density-functional theory of fluids. In the second case, we study the formation and stability of lanes under the influence of time-varying (rotating) fields. Lanes are stable kinetic structures formed in colloidal mixtures composed by opposite charged particles subjected to counterflow imposed by a uniform external field. We find that these structures resist the rotation of the field for small angles (increasing the shift between the lanes orientation and the direction of the field) but they are destroyed and rearranged into lanes along new orientations according to quantized angles (the magic angles) in a system with periodic boundary conditions. The evolution is constrained by these magic angles and has a dependence on the angular velocity of the field and its intensity. We also employ the Voronoi tessellation method to identify the clusters during the evolution and find that both the number of clusters and the distribution of the area of the Voronoi cells depend on the state of the system. When the evolution is trapped in a lane configuration the number of clusters is minimal and there is a greater number of small cells compared with the mixed state in which particles move along the field direction. |
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