title: Quantification of physical (roughness) and chemical (dielectric constant) leaf surface properties relevant to wettability and adhesion.
abstract: BACKGROUND
  Spray droplet adhesion is dependent not only on formulation and droplet parameters but also on the surface properties (physical and chemical) of the leaf. Quantifying these leaf surface properties would aid understanding and modelling of adhesion, helping to optimise spray formulations. Fractal dimensions (FDs) were used to quantify the relative leaf surface roughness of ten plant species. Static droplet contact angles were measured on each leaf surface, and wetting tension was calculated. Chemical profiles of the leaf surfaces were developed by evaluating contact angle behaviour relative to solution dielectric constants.
  
  
  RESULTS
  The FDs of Cryo-SEM micrographs taken at 300× magnification gave the best correlation with adhesion. The wetting tension intercept had a strong relationship with mean adhesion, and successfully accounted for the wettability of the outlier species.
  
  
  CONCLUSIONS
  The microroughness of the leaf surface, as revealed by Cryo-SEM, can be quantified by fractal dimension analysis. However, the wetting tension intercept is a more useful universal measure of the surface properties of the leaf (including roughness) as they pertain to adhesion. The slope of the wetting tension versus dielectric constant plot allowed preliminary quantification of the chemical contribution of leaf surface dielectric behaviour to adhesion.
authors.affiliation: Plant Protection Chemistry NZ Ltd, Rotorua, New Zealand.
authors.forename: Justin J
authors.initials: JJ
authors.lastname: Nairn
authors.forename: W Alison
authors.initials: WA
authors.lastname: Forster
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: van Leeuwen
mesh_terms: D000268:Adhesiveness; D020285:Cryoelectron Microscopy; D005559:Formamides / Q000737:chemistry; D017709:Fractals; D007091:Image Processing, Computer-Assisted; D018515:Plant Leaves / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure; D018521:Plant Physiological Phenomena; D010944:Plants / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D017155:Wettability
chemical_list: D005559:Formamides; D012996:Solutions