Controlling Droplet-Size Distribution Using Oil Emulsions in Agricultural Sprays

Qin, Kuide; Tank, Holger; Wilson, S. A.; Downer, Brandon; Liu, Lei

doi:10.1615/atomizspr.v20.i3.40

Cited by 41 publications

(24 citation statements)

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“…However, we mention that even if the spreading of oil droplets at the interface is not the limiting step for the perforation, it is nevertheless crucial as several studies have emphasized that solid particles that enter the air/aqueous phase interface but do not spread at the interface do not lead to the perforation of liquid sheets. 2,31 Overall, our work has allowed one to establish the physical mechanisms at the origin of the antidrift properties of dilute oil in water emulsions and in turn propose new routes to develop novel and more efficient formulations for antidrift emulsion adjuvants.…”

Section: Resultsmentioning

confidence: 98%

“…A more favorable situation occurs for local fluctuations ξ of the interface profile; as a simple ansatz we use the Gaussian profile ξ = D * e −ρ 2 /R 2 with the lateral length scale R. Its energy consists of electrostatic and capillary contributions. In small gradient approximation, ∇ξ ∼ D * /R ≤ 1, the capillary energy (γ/ 2)∫ dS(∇ξ) 2…”

Section: Discussionmentioning

confidence: 99%

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Playing with Emulsion Formulation to Control the Perforation of a Freely Expanding Liquid Sheet

et al. 2017

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A single-drop experiment based on the collision of one drop of liquid on a small solid target is used to produce liquid sheets that are visualized with a fast camera. Upon impact, the drop flattens into a sheet that is bounded by a thicker rim and radially expanding in air. Emulsion-based liquid sheets are destabilized through the nucleation of holes that perforate the sheet during its expansion. The holes grow until they merge together and form a web of ligaments, which are then destabilized into drops. We propose the perforation mechanism as a sequence of two necessary steps. The emulsion oil droplets first enter the air/water interface, and then spread at the interface. We show that the formulation of the emulsion is a critical parameter to control the perforation as the addition of salt or amphiphilic copolymers can trigger or completely inhibit the perforation mechanism. We demonstrate that the entering of the droplets at the air/water interface is the limiting step of the mechanism. Thin-film forces such as electrostatic or steric repulsion forces stabilize the thin film formed between the interface and the approaching oil droplets, thus preventing the entering of droplets at the interface and in turn inhibiting the perforation process. We theoretically rationalize the successive steps in the approach and entering of an oil droplet at the film interface and the role of salt and amphiphilic polymer in the different steps.

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Section: Resultsmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Playing with Emulsion Formulation to Control the Perforation of a Freely Expanding Liquid Sheet

et al. 2017

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“…The occurrence of perforation events in a spray directly decreases the fraction of small drops issued from the spray [8] as illustrated in the case of dilute emulsions, which are prone to induce the bursting of liquid sheets [7]. Dilute emulsions are also recognized as anti-drift adjuvants [8][9][10][11] and therefore commonly used as carrier fluids for pesticides delivery. Controlling the perforation processes would therefore allow one to finely tune the size distribution of drops issued from sprays, a goal of uttermost importance in many industrial processes.…”

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confidence: 99%

Bursting of Dilute Emulsion-Based Liquid Sheets Driven by a Marangoni Effect

2015

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We study the destabilization mechanism of thin liquid sheets expanding in air and show that dilute oil-in-water emulsion-based sheets disintegrate through the nucleation and growth of holes that perforate the sheet. The velocity and thickness fields of the sheet outside the holes are not perturbed by holes and hole opening follows a Taylor-Culick law. We find that a pre-hole, which widens and thins out the sheet with time, systematically precedes the hole nucleation. The growth dynamics of the pre-hole follows the law theoretically predicted for a liquid spreading on another liquid of higher surface tension due to Marangoni stresses. Classical Marangoni spreading experiments quantitatively corroborate our findings.The destabilization of free liquid films is of great importance for aerosol dispersions, and is involved in many practical situations [1,2] [6], and dilute oil-in-water emulsions [7]. However, despite its relative ubiquity, the bursting of liquid sheets through perforation events have not yet been carefully investigated nor modeled. The occurrence of perforation events in a spray directly decreases the fraction of small drops issued from the spray [8] as illustrated in the case of dilute emulsions, which are prone to induce the bursting of liquid sheets [7]. Dilute emulsions are also recognized as anti-drift adjuvants [8][9][10][11] and therefore commonly used as carrier fluids for pesticides delivery. Controlling the perforation processes would therefore allow one to finely tune the size distribution of drops issued from sprays, a goal of uttermost importance in many industrial processes. In this optics, a physical description of the mechanisms at play in perforation processes is desired. The commonly invoked conditions for perforation include a dewetting of inclusions by the fluid and an inclusion diameter equal to, or larger than, the thickness of the liquid sheet, so that inclusions cause perforation by puncturing both interfaces of the sheet [3]. But, to the best of our knowledge, those conditions have never been confronted to robust experimental facts. To unambiguously clarify the physical mechanisms at play, rationale experiments on individual perforation events are therefore required.In this Letter, we investigate the perforation mechanisms of an emulsion-based free liquid sheet issued from a single-drop experiment; resulting from the impact of one drop of fluid onto a small target [12][13][14]. During the sheet expansion, holes nucleate and grow. We show that each perforation event is preceded by the formation of a pre-hole that thins out the sheet and widens with time. We demonstrate that the pre-hole growth is governed by a Marangoni effect. The entry of emulsion oil droplets at the air/water interface leads to a spreading of the oil due to a surface tension gradient stress. This stress is counterbalanced by a viscous stress that drags the subsurface fluid, whose flow causes a local film thinning which ultimately lead to the rupture of the film. We show that the growth kinetics of pre-holes ...

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“…These formulations likely share a common mechanism for affecting spray atomization on the basis of this physical property [29]. However, current scientific literature is inconclusive regarding the effect of solid dispersions on droplet size, and therefore drift [12,14,[29][30][31]. This study provides evidence that spray solutions of formulations with solid particles do influence drift, and that drift of the WP formulation was greater than for sprays of water alone.…”

Section: Discussionmentioning

confidence: 69%

Peer Review #2 of "Effect of insecticide formulation and adjuvant combination on agricultural spray drift (v0.1)"

2019

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Losses of crop protection products when agricultural spray applications drift has economic and ecological consequences. Modification of the spray solution through tank additives and product formulation is an important drift reduction strategy that could mitigate these effects, but has been studied less than most other strategies. Therefore, an experimental field study was conducted to evaluate spray drift resulting from agricultural ground applications of an insecticide formulated as a suspension concentrate and as a wettable powder, with and without two adjuvants. Droplet sizes were also measured in a wind tunnel to determine if indirect methods could be substituted for field experimentation to quantify spray drift from these technologies. Results suggest that spray drift was reduced by 37% when comparing the suspension concentrate to the wettable powder formulation. As much as 63% drift reduction was achieved by incorporating certain spray adjuvants, but this depended on the formulation/adjuvant combination. The wind tunnel data for droplet spectra showed strong agreement with field deposition trends, suggesting that droplet statistics could be used to estimate drift reduction of spray solutions. These findings can be used to develop a classification scheme for formulated products and tank additives based on their potential for reducing spray drift.

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Controlling Droplet-Size Distribution Using Oil Emulsions in Agricultural Sprays

Cited by 41 publications

References 0 publications

Playing with Emulsion Formulation to Control the Perforation of a Freely Expanding Liquid Sheet

Playing with Emulsion Formulation to Control the Perforation of a Freely Expanding Liquid Sheet

Bursting of Dilute Emulsion-Based Liquid Sheets Driven by a Marangoni Effect

Peer Review #2 of "Effect of insecticide formulation and adjuvant combination on agricultural spray drift (v0.1)"

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