title: Effect of water absorption on pollen adhesion.
abstract: Pollens possess a thin liquid coating, pollenkitt, which plays a major role in adhesion by forming capillary menisci at interfaces. Unfortunately, the influence of humidity on pollenkitt properties and capillary adhesion is unknown. Because humidity varies widely in the environment, the answers have important implications for better understanding plant reproduction, allergy and asthma, and pollen as atmospheric condensation nuclei. Here, pollenkitt-mediated adhesion of sunflower pollen to hydrophilic and hydrophobic surfaces was measured as a function of humidity. The results quantify for the first time the significant water absorption of pollenkitt and the resulting complex dependence of adhesion on humidity. On hydrophilic Si, adhesion increased with increasing RH for pollens with or without pollenkitt, up to 200nN at 70% RH. In contrast, on hydrophobic PS, adhesion of pollenkitt-free pollen is independent of RH. Surprisingly, when pollenkitt was present adhesion forces on hydrophobic PS first increased with RH up to a maximum value at 35% RH (∼160nN), and then decreased with further increases in RH. Independent measurement of pollenkitt properties is used with models of capillary adhesion to show that humidity-dependent changes in pollenkitt wetting and viscosity are responsible for this complex adhesion behavior.
authors.affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, GA 30332-0100, United States.
authors.forename: Haisheng
authors.initials: H
authors.lastname: Lin
authors.affiliation: School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta, GA 30332-0400, United States.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Lizarraga
authors.affiliation: School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta, GA 30332-0400, United States. Electronic address: lawrence.bottomley@chemistry.gatech.edu.
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Bottomley
authors.affiliation: School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, GA 30332-0100, United States. Electronic address: carson.meredith@chbe.gatech.edu.
authors.forename: J
authors.initials: J
authors.lastname: Carson Meredith
keywords: Adhesion; Atomic force microscopy; Capillary forces; Force spectroscopy; Humidity; Microcantilever sensor; Pollenkitt; Sunflower pollen