title: Spreading dynamics and dynamic contact angle of non-Newtonian fluids.
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 xi3/(n+2) (xi is the distance from the contact line), whereas in the gravitational regime, h is proportional to xi1/(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.
authors.affiliation: Department of Thermal Engineering, School of Mechanical Engineering, University of Science & Technology Beijing, Beijing 100083, China.
authors.forename: X D
authors.initials: XD
authors.lastname: Wang
authors.forename: D J
authors.initials: DJ
authors.lastname: Lee
authors.forename: X F
authors.initials: XF
authors.lastname: Peng
authors.forename: J Y
authors.initials: JY
authors.lastname: Lai