title: Influence of surface orientation on the organization of nanoparticles in drying nanofluid droplets.
abstract: The influence of droplet orientation on the flow directed organization of nanoparticles in evaporating nanofluid droplets is important for the efficiency of foliar applied fertilizers and contamination adhesion to the exterior of buildings. The so called "coffee ring" deposit resulting from the evaporation of a sessile nanofluid drop on a hydrophilic surface has received much attention in the literature. Deposits forming on hydrophobic surfaces in the pendant drop position (i.e. hanging drop), which are of importance in foliar fertilizer and exterior building contamination, have received much less attention. In this study, the deposit patterns resulting from the evaporation of water droplets containing silica nanoparticles on hydrophobic surfaces orientated in the sessile or pendant configuration are compared. In the case of a sessile drop the well known coffee ring pattern surrounding a thin nanoparticle layer was formed. A deposit consisting of a thin coffee ring surrounding a bump was formed in the pendant position. A mechanism involving flow induced aggregation at the droplet waist, settling, orientation dependant accumulation within the drop and pinning of the contact line is suggested to explain the findings. Differences in the contact area and adhesion of deposits with surface orientation will affect the efficiency and rainfastness of foliar fertilizers and the cleanliness of building exteriors.
authors.affiliation: School of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Marc A
authors.initials: MA
authors.lastname: Hampton
authors.forename: Tuan A H
authors.initials: TA
authors.lastname: Nguyen
authors.forename: Anh V
authors.initials: AV
authors.lastname: Nguyen
authors.forename: Zhi Ping
authors.initials: ZP
authors.lastname: Xu
authors.forename: Longbin
authors.initials: L
authors.lastname: Huang
authors.forename: Victor
authors.initials: V
authors.lastname: Rudolph
mesh_terms: D057927:Hydrophobic and Hydrophilic Interactions; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D012822:Silicon Dioxide