title: Effect of TiO2 nanoparticles on contact line stick-slip behavior of volatile drops.
abstract: We describe an experimental investigation of the concomitant evaporation and (de)wetting behavior of sessile drops of ethanol, either pure, or containing small amounts of titanium oxide nanoparticles. Pure ethanol behaved in a more or less "ideal" manner, with constantly decreasing contact radius, at essentially constant contact angle. However, distinct "stick-slip" pinning behavior of the triple line occurred when nanoparticles were added to the base liquid. Increased nanoparticle concentration enhanced the "stick-slip" behavior. The observed behavior is attributed to the effects of particle accumulation near the contact line, caused by the now-established advective flow during evaporation. "Slip" behavior can be explained by hysteretic energy barriers, somewhat akin to line tension. The "stick" behavior was not complete: some triple line drift occurred ("pseudo-pinning"). It is postulated that this may be due to small-scale pinning of the triple line by deposited particles, or to increased effective viscosity due to high, local nanoparticle concentrations.
authors.affiliation: School of Engineering, The University of Edinburgh, The Kings Buildings, Mayfield Road, Edinburgh, EH9 3JL United Kingdom. Ross.Moffat@ed.ac.uk
authors.forename: J Ross
authors.initials: JR
authors.lastname: Moffat
authors.forename: Khellil
authors.initials: K
authors.lastname: Sefiane
authors.forename: Martin E R
authors.initials: ME
authors.lastname: Shanahan