title: Effect of Salt Concentration on the Motion of Particles near the Substrate in Drying Sessile Colloidal Droplets.
abstract: The motions of the particles on the substrate of a drying sessile colloidal droplet of water were measured using multiparticle tracking. Droplets with different concentrations (0-250 mM) of sodium chloride (NaCl) were compared. Several statistical quantities were proposed to characterize the heterogeneous behaviors of the particles and distinguish the effects of the flow field and the substrate interaction. For the salt-free droplet, most of the particles were nonadsorbed and mobile without friction. With the presence of salt, the fraction of the adsorbed particles increases with increasing evaporation time and the initial salt concentration, which was explained by Derjaguin-Landau-Verwey-Overbeek interaction. The fraction of mobile particles is mostly frictionless for all samples. At low salt concentrations, the velocity of mobile particles increases with the evaporation time to a peak and then decreases. The velocity is lower for higher salt concentrations. The effect of salt on the nonadsorbed particles was attributed to the electrokinetic effect.
authors.affiliation: Research Institute of Materials Science, ‡State Key Laboratory of Luminescent Materials and Devices, and §State Key Laboratory of Pulp and Paper Engineering, South China University of Technology , Guangzhou 510640, China.
authors.forename: Guozhi
authors.initials: G
authors.lastname: Xu
authors.affiliation: Research Institute of Materials Science, ‡State Key Laboratory of Luminescent Materials and Devices, and §State Key Laboratory of Pulp and Paper Engineering, South China University of Technology , Guangzhou 510640, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Hong
authors.affiliation: Research Institute of Materials Science, ‡State Key Laboratory of Luminescent Materials and Devices, and §State Key Laboratory of Pulp and Paper Engineering, South China University of Technology , Guangzhou 510640, China.
authors.forename: Weixiang
authors.identifier: 0000-0001-6964-8313
authors.initials: W
authors.lastname: Sun
authors.affiliation: Research Institute of Materials Science, ‡State Key Laboratory of Luminescent Materials and Devices, and §State Key Laboratory of Pulp and Paper Engineering, South China University of Technology , Guangzhou 510640, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Wang
authors.affiliation: Research Institute of Materials Science, ‡State Key Laboratory of Luminescent Materials and Devices, and §State Key Laboratory of Pulp and Paper Engineering, South China University of Technology , Guangzhou 510640, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Tong