Fluid Mechanics Seminar: Maziyar Jalaal
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Droplet impact and spreading on dry and wet surfaces occurs in a wide variety of industrial applications. Examples include, but not limited to, ink-jet printing, spray coatings, crop spraying, and surface cooling. In this presentations, I will talk about the controlled spreading of droplets of complex fluids. Firstly, we will provide some theoretical analysis on spreading of yield stress fluids where we employ lubrication theory, asymptotic solutions, and numerical simulations to explain the dynamics and final static shape of a viscoplastic droplet on a solid horizontal surface. We provide experimental data to verify our theoretical solutions. In our experiments, we first provide a method to eliminate the apparent slip of the yield stress fluid. The method uses a chemical modification of glass surfaces to generate permanent positive charges, resulting in a no-slip boundary condition. We then perform shadowgraphy experiments to measure the final radius of the droplets under different conditions such as extruding and impacting droplets. We compare the theoretical and experimental results and discuss the similarities and differences.
Secondly, we provide a comprehensive rheological characterization of a particular thermo-responsive fluid, Pluronic F127. We show that the aqueous solution of the polymer undergoes a sol(Newtonian)-gel(yield stress) transition upon heating. We further characterize the properties of the gel in detail. Finally, we show one can thermally trigger a droplet of this thermo-responsive solution to externally control the final shape of the droplet on a surface. In short, the final radius of the droplet can be controlled by heating the surface; for a given concentration, the larger the surface temperature, the smaller the final shape of a droplet. In the same part of the presentation, we introduce an experimental method based on optical coherence tomography to identify the solidified region inside a droplet.
Bio: Mazi Jalaal is a PhD candidate and Vanier CGS scholar in the Department of Mechanical Engineering under the supervision of Neil Balmforth and Boris Stoeber. He started his PhD in September 2012 and will be defending his thesis in November.
Additional Information
Location: ESB 2012
Maziyar Jalaal, University of British Columbia
Maziyar Jalaal, University of British Columbia