Spreading dynamics and dynamic contact angle of non-newtonian fluids
Journal
Langmuir
Journal Volume
23
Journal Issue
15
Pages
8042-8047
Date Issued
2007
Author(s)
Abstract
The spreading dynamics of power-law fluids, both shear-thinning and shear-thickening fluids, that completely or partially wet solid substrate was investigated theoretically and experimentally. An evolution equation for liquid-film thickness was derived using a lubrication approximation, from which the dynamic contact angle versus the contact line moving velocity relationship was evaluated. In the capillary spreading regime, film thickness h is proportional to £i 3/(n+2) (£i is the distance from the contact line), whereas in the gravitational regime, h is proportional to £i1/(n+2) relating to the rheological power exponent n. The derived model fit the experimental data well for a shear-thinning fluid (0.2% w/w xanthan solution) or a shear-thickening fluid (7.5% w/w 10 nm silica in polypropylene glycol) on a completely wetted substrate. The derived model was extended using Hoffmann's proposal for partially wetting fluids. Good agreement was also attained between model predictions and the shear-thinning fluid (1% w/w cmc solution) and shear-thickening fluid (10% w/w 15 nm silica) on partially wetted surfaces. ? 2007 American Chemical Society.
Type
journal article