Abstract :
[en] Drop behaviour during impact affects retention. The increase of adhesion is usually seen as
the objective when applying crop protection products, while bouncing and shattering are seen as
detrimental to spray retention. However, observation of drop impacts on barley (Hordeum vulgare L.)
using high speed shadowgraphy shows that bouncing and fragmentation can occur in Cassie-Baxter as
well as in Wenzel wetting regimes. In this last regime, a part of the drop may remain stuck on the
surface, contributing to retention. Using simultaneous measurements of drop impacts with high speed
imaging and of retention with fluorophotometry for spray mixtures on excised barley leaves using a
Teejet 11003 nozzle at 0.2 MPa, it is observed that about 50% of the drops that fragmented in the
Wenzel state remain on the horizontal leaf. Depending on the spray mixture, these impact outcomes
accounted for 28 to 46% of retention, the higher contribution being correlated with bigger VMD
(Volume Median Diameter). This contribution is not negligible and should be considered when
modelling spray retention processes.
Commentary :
- We investigated retention for drops splashing in the Wenzel wetting regime
- 45 to 58 % of the volume of these drops remained on the leaf after impact
- This contributed from 28 to 46% of the retention on barley, and was a function of
formulation and VMD
- The contribution of these drops should be included in process-based retention models
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