STUDIES ON WETTING PHENOMENA ON PLANT LEAF SURFACES .3. A RETENTION MODEL FOR DROPLETS ON SOLID-SURFACES

To investigate the factors governing retention of pesticidal spray solutions on plant surfaces, a new retention model for droplets on solid surfaces has been introduced as V-rho-g sin-alpha = 27-pi-r-gamma-1(sin THETA(a) + sin THETA(r) (DELTA-THETA/pi-2 - DELTA-THETA-2), where DELTA-THETA = THETA(a)-THETA(r). The minimum sliding volumes (MiSV) of surfactant aqueous solutions (2 g litre-1; surface tensions; 28.5-72.5 mN m-1) on smooth surfaces of paraffin wax and polymer sheets were measured and the validity of the above retention equation was verified on combinations of these solutions and surfaces. A concept of the specific adhesional force (F(s)) of a droplet was defined as F(s) = pi-gamma-1(sin THETA(a) + sin THETA(r) (DELTA-THETA/pi-2-DELTA-THETA-2), which was the maximum adhesional force on a unit length of the width of the contact circle of a droplet, and F(s) values of the solutions on the surfaces were compared. The predominant factors for droplet retention are discussed on the basis of this model.