Particle Removal from Surfaces using Rinsing Flows with Extensional Viscosity Liquids

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Fuller0930100"Rinsing flows" are where one fluid ablates a layer of a second, miscible liquid that coats a solid substrate. This process is common to everyday experience and to many industrial processes, particularly in cleaning operations. This flow arrangement is accompanied by a classic, "hydraulic jump" phenomenon but the stratification of two liquids, with differing viscosities, leads to qualitatively new results. A particular interest in this study is during the cleaning of colloidal particles from solid, planar substrates when the liquid coating the substrate (the one being rinsed off) is non-Newtonian. Preliminary data are offered that demonstrate that non-Newtonian polymer and surfactant solutions with large strain thickening extensional viscosities very effectively "pluck" adsorbed colloidal particles from planar surfaces. However, this can only be accomplished by rinsing flows that contain extensional flow gradients. This research will explore the fluid mechanics of rinsing flows as a function of the viscosity ratio of the two fluids (the coating liquid and the jet liquid) and as a function of the rheological character of the coating liquids using high-speed photography and particle tracking. The dynamics of particle removal in real time will also be directly measured. Another important consideration is the hydrophobicity of the solid substrates onto which the rinsing flows are applied. The PI's preliminary data demonstrate that the surface energy of the substrates has a profound effect on the process of inertial dewetting and this research will explore this phenomenon. The PI's previous NSF sponsored research has stimulated a number of initiatives that broadened the impact of the PI's scholarly activities. In addition to participating in a REU program at the university, for the past four summers the PI has extended opportunities to local high school students. Positions have been made available to students from Eastside Preparatory School in East Palo Alto and Harker School in Sunnyvale. This work is jointly funded by the Fluid Dynamics and Particulate and Multiphase Programs of CBET.