Surface tension driven flow is studied in films of viscous polymer liquid by monitoring the spreading of droplets or the capillary levelling of films with excess surface area. The research presented in this thesis is focused on three major themes where molecular details are important to flow: molecular anisotropy, interfacial friction, and the initial state of the film.
The effect of molecular anisotropy is studied by examining the dynamics of partially wetting diblock copolymer droplets using optical microscopy. The shape of the droplets is measured as they evolve towards equilibrium. In this system, it is found that energy is dissipated at the base of the droplets. This is consistent with a reduced interfacial friction at the liquid-substrate interface.
Flow dynamics are also found to depend on the symmetry of the initial film thickness profile. Thickness perturbations with different degrees of symmetry were created in an initially flat film using focused laser spike annealing. The films were allowed to flow under the driving force of surface tension, and using atomic force microscopy, the film thickness profile was measured as a function of time. We find the depth of the perturbations decreases as a power law in time, with a power law exponent that depends on the symmetry of the thickness perturbation.
The role of interfacial effects are explored by studying the flow in a film with zero interfacial friction: a freely-suspended film. Flow is measured in films with no interfacial friction using a technique which creates a film with a sharp step in the initial thickness profile. The excess surface area at the edge of the step drives flow, and information about the dynamics of the fluid is obtained by measuring the width of the step over time with atomic force microscopy. We observe flow that is consistent with plug flow: where the velocity of the fluid in the plane of the film is constant along the direction perpendicular to the film.
Finally, freely-suspended films provide a model system to study the nucleation and growth of pores in a membrane. By purposefully creating pores of different initial size, the critical radius for nucleation is measured as a function of the membrane thickness. The experimental results agree with a simple model in which the free energy cost at the perimeter of a pore is determined by the excess surface area due to the curved interface of the pore edge. / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/18686 |
| Date | January 2016 |
| Creators | Ilton, Mark |
| Contributors | Dalnoki-Veress, Kari, Physics and Astronomy |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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