Rodd, Lucy E.; Scott, Timothy P.; Cooper-White, Justin J.; McKinley, Gareth H.
Submitted to Applied Rheology, August 2004
(1522618 bytes; application/pdf) - 23-jun-2010
Rodd, Lucy E.; Scott, Timothy P.; Boger, David V.; Cooper-White, Justin J.; McKinley, Gareth H.
The non-Newtonian flow of dilute aqueous polyethylene oxide (PEO) solutions through
microfabricated planar abrupt contraction-expansions is investigated. The contraction
geometries are fabricated from a high-resolution chrome mask and cross-linked PDMS
gels using the tools of soft-lithography. The small length scales and high deformation
rates in the contraction throat lead to significant extensional flow effects even with dilute polymer solutions having time constants on the order of milliseconds. The dimensionless
extra pressure drop across the contraction increases by more than 200% and is
accompanied by significant upstream vortex growth. Streak photography and videomicroscopy
using epifluorescent particles shows that the flow ultimately becomes
unstable and three-dimensional. The moderate Reynolds numbers...
(10453154 bytes; application/pdf) - 23-jun-2010
Stocker, Roman; Hosoi, A.E.
A lubrication-flow model for a free film in a corner is presented. The model, written in the hyperbolic coordinate system ξ = x² – y², Î· = 2xy, applies to films that are thin in the Î· direction. The lubrication approximation yields two coupled evolution equations for the film thickness and the velocity field which, to lowest order, describes plug flow in the hyperbolic coordinates. A free film in a corner evolving under surface tension and gravity is investigated. The rate of thinning of a free film is compared to that of a film evolving over a solid substrate. Viscous...
(2587476 bytes; application/pdf) - 23-jun-2010
Hosoi, A.E.; Mahadevan, L.
We consider the dynamics of an elastic sheet lubricated by the flow of a thin layer of fluid that separates it from a rigid wall. By considering long wavelength deformations of the sheet, we derive an evolution equation for its motion, accounting for the effects of elastic bending, viscous lubrication and body forces. We then analyze various steady and unsteady problems for the sheet such as peeling, healing, levitating and bursting using a combination of numerical simulation and dimensional analysis. On the macro-scale, we corroborate our theory with a simple experiment, and on the micro-scale, we analyze an oscillatory valve...
(938640 bytes; application/pdf) - 23-jun-2010