The evaporation of sessile drops of water and n-decane placed on various substrates has been studied using a projection method. Drop dimensions and contact angle have been measured as a function of time. The first stage of the experiment corresponds to a saturated atmosphere; then, when evaporation is allowed to occur, two or three different stages appear (depending on the surface roughness). For the first of these, a model is proposed which allows us to calculate the coefficient of diffusion of the liquid vapor in air.

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The dynamics of the three-phase contact line for water and ethanol is experimentally investigated using substrates of various hydrophobicities. Different evolutions of the droplet profile (contact line, R, and contact angle, θ) are found to be dependent on the hydrophobicity of the substrate. A simple theoretical approach based on the unbalanced Young force is used to explain the depinning of the contact line on hydrophilic surfaces or the monotonic slip on hydrophobic substrates. The second part of the article involves the addition of different quantities of titanium oxide nanoparticles to water, and a comparison of the evaporative behavior of these novel fluids with the base liquid (water) on substrates varying in hydrophobicity (i.e., silicon, Cytop, and PTFE) is presented. The observed stick-slip behavior is found to be dependent on the nanoparticle concentration. The evaporation rate is closely related to the dynamics of the contact line. These findings may have an important impact when considering the evaporation of droplets on different substrates and/or those containing nanoparticles.