Tesis doctoral de Maximiliano Andrés Giuliani
In this experimental work, we present a study on the dynamics of the crystallisation of colloidal suspension. We studied two experimental setups: vertical deposition configuration and spin-coating. The vertical deposition setup permits to apply electric fields in a configuration similar to a parallel plate capacitor. We used polystyrene particles (1.3 µm in diameter) suspended in ultrapure water at low volume fractions (0.1% to 0.5%). The experiments were carried out at controlled temperature 63 ◦ c and low humidity (below 2 %rh). We also applied weak electric fields (0.2 to 0.6 v/mm) to study their effect on the dynamics. We measured the velocity of growth of different structures at the different experimental conditions. We observed that, at low concentration 0.1%, there is only one characteristic velocity that we associate with two extreme structures, a very sparse deposit and a compact monolayer. For the higher concentration studied (0.3 % and 0.5 %) we found that a new characteristic velocity of larger magnitude appears. This velocity is associated with a sub-monolayer structure forming bands a few particles wide. We observed multilayer structures that can grow at high or low velocity. In the presence of electric fields, the characteristic velocities are little modified, although we identified interesting structuring of some deposits in parallel lines of highly periodic spacing. We concluded that the complex dynamics associated to this system is due to the different parameters that affect the deposition process: type of structure deposited above the contact line, local concentration near the contact line and intensity of the interaction between the particle and the substrate. in the spin-coating setup, we used 458 nm diameter spheres dispersed on acetone or methyl ethyl ketone. The high volatility of the fluids and the thin layer induced by the rotation of the substrate gave a rapid dynamics (< 2 s). The concentration of the suspension mainly was 20 %. Some experiments at lower concentration were performed, but it was observed that static results were equivalent to increase the rotation rate of the substrate. The dynamics was recorded with a high speed camera. We characterised the thinning rate and the long range orientational order dynamics during the fluid stage, as well as the drying front dynamics. We also characterised the radial thickness profiles of the dried deposits and their symmetry. We extended the model of emslie [9] to volatile fluids and found that gives an excellent fit to the experimental data of the thinning rate as a function of time. We also observed a transition from a 6- to a 4-fold symmetry in the fluid stage that correlates well with the transition from the non-evaporative to the evaporative stage extracted from the fit. We observe a transition in the morphology of the bright arms of the dried deposit. Near the centre they are generally well defined, while as the speed is increased, their definition decrease in the outer region. This transition correlates well with an increase in the relevance of capillary forces with respect to the viscous forces at the time of crystallisation. We conclude that the balance between radial and evaporative flows are responsible of the different observed symmetries.
Datos académicos de la tesis doctoral «Colloidal crystal formation through interfacial mechanisms«
- Título de la tesis: Colloidal crystal formation through interfacial mechanisms
- Autor: Maximiliano Andrés Giuliani
- Universidad: Navarra
- Fecha de lectura de la tesis: 24/09/2010
Dirección y tribunal
- Director de la tesis
- Wenceslao González Viñas
- Tribunal
- Presidente del tribunal: felix Ritort farran
- jordi Ignés mullol (vocal)
- anand Yethiraj (vocal)
- Antonio Fernández barbero (vocal)