Pesticide additives cause drifting droplets, but can be controlled

Mar 20, 2012 by Brian Wallheimer
Simulations and high-speed visualization reveal a synergistic effect between chemical additives that can lead to the formation of satellite droplets during crop spraying. Emission of satellite droplets - shown here between two main drops - is also detrimental in a number of applications ranging from food processing to rocket propulsion systems. (Purdue University image)

(PhysOrg.com) -- Chemical additives that help agricultural pesticides adhere to their targets during spraying can lead to formation of smaller "satellite" droplets that cause those pesticides to drift into unwanted areas, Purdue University researchers have found.

Carlos Corvalan, an associate professor of , said understanding how the additives work together means they could be designed to decrease the health, environmental and property damage risks caused by drift. Corvalan; Osvaldo Campanella, a Purdue professor of agricultural and ; and Paul E. Sojka, a Purdue professor of mechanical engineering, published their results in a February issue of the journal Chemical Engineering Science.

"When we spray liquids, we have what we call main drops, which are drops of the desired size, and we can also have smaller satellite drops. The smaller drops move easily by wind and travel ," Corvalan said. "Now that we know better how additives influence the formation of satellite droplets, we can control their formation."

The research will also have applications in food processing and rocket propulsion, where drop sizes are important.

When liquids are sprayed, they start in a stream and eventually form drops. As the liquids move farther in the air, drops connected by a thin filament start to pull apart. That filament eventually detaches and becomes part of the drops that were forming on either side of it.

Satellite droplets form in the middle of of pesticides containing surfactants and polymeric additives, which help the pesticides wet and adhere to plant surfaces. The surfactants reduce and force round drops to flatten, helping them cover more surface area on a sprayed plant's leaves. The polymeric additives reduce viscosity – liquid resistance – making the pesticide flow easier. Polymeric additives also keep the drops from bouncing off plant surfaces.

"Each additive is designed to improve the characteristics of the main drops," Corvalan said. "But there is a side effect."

When both additives are present in a pesticide, the surfactant pushes more liquid toward the filament. The reduced viscosity allows liquid to flow more easily in that direction, resulting in a well-defined satellite drop forming in the filament.

"When you put both additives together, there is a synergistic effect. The force induced by the surfactant that was opposed by viscosity is no longer so strongly opposed, and this combined effect can result in the formation of satellite droplets," Corvalan said.

Drifting of not only increases waste and cost for farmers but also can cause health, environmental and property damage, according to the U.S. Environmental Protection Agency.

The results show that carefully modulating the strength, concentration or ratio of surfactants to polymer additives can mitigate or eliminate the formation of unwanted satellite .

Corvalan is now transferring the results obtained from agricultural research into food processing and work. He said drop size uniformity is as important for fuels sprayed into rocket combustion chambers as for the production of food emulsions.

Explore further: IHEP in China has ambitions for Higgs factory

More information: Threshold Wavelength on Filaments of Complex Fluids, Rajeswari J. Muddu, Jiakai Lu, Paul E. Sojka, Carlos M. Corvalan, Chemical Engineering Science.

ABSTRACT
The breakup into drops of complex-fluid filaments – usually jets of polymeric and surfactant solutions – plays a central role in many engineering applications ranging from crop spraying to food processing and propulsion systems. To assess the influence of interfacial perturbations in the breakup process, we followed the dynamics of the initial wavelength of surface instability on complex-fluid filaments using direct numerical simulation. We found a threshold wavelength at low Reynolds numbers corresponding to a change on the filament's configuration near breakup from large primary drops connected by slender liquid threads for wavelengths below the threshold to clearly defined satellite drops in between the primary drops for wavelengths larger than the threshold. We also found that shear-thinning effects, by reducing the viscous resistance to the Marangoni stress responsible for the formation of the satellites, cause the threshold to appear at shorter wavelengths.

Related Stories

Researchers cooking up new gelled rocket fuels

Jan 21, 2009

Engineers and food scientists are teaming up to develop a new type of gelled fuel the consistency of orange marmalade designed to improve the safety, performance and range of rockets for space and military ...

Why do dew drops do what they do on leaves?

Jan 11, 2012

Nobel laureate poet Rabindranath Tagore once wrote, "Let your life lightly dance on the edges of time like dew on the tip of a leaf." Now, a new study is finally offering an explanation for why small dew drops ...

Emulsion with a round-trip ticket

Jun 14, 2007

Oil and water are not miscible. However, it is possible to combine both into an emulsion in which they act as a unit—for example, in creams, body lotion, milk, or mayonnaise. In these substances, one of the two liquids ...

Droplets that Roll Uphill

Sep 24, 2007

A recent experiment conducted by physicists at University of Bristol in the United Kingdom has shown that liquid drops can defy gravity. Droplets of liquid on an inclined plate that is shaken up and down can ...

Recommended for you

New approach to form non-equilibrium structures

3 hours ago

Although most natural and synthetic processes prefer to settle into equilibrium—a state of unchanging balance without potential or energy—it is within the realm of non-equilibrium conditions where new possibilities lie. ...

Nike krypton laser achieves spot in Guinness World Records

5 hours ago

A set of experiments conducted on the Nike krypton fluoride (KrF) laser at the U.S. Naval Research Laboratory (NRL) nearly five years ago has, at long last, earned the coveted Guinness World Records title for achieving "Highest ...

Chemist develops X-ray vision for quality assurance

9 hours ago

It is seldom sufficient to read the declaration of contents if you need to know precisely what substances a product contains. In fact, to do this you need to be a highly skilled chemist or to have genuine ...

The future of ultrashort laser pulses

9 hours ago

Rapid advances in techniques for the creation of ultra-short laser pulses promise to boost our knowledge of electron motions to an unprecedented level.

IHEP in China has ambitions for Higgs factory

Jul 23, 2014

Who will lay claim to having the world's largest particle smasher?. Could China become the collider capital of the world? Questions tease answers, following a news story in Nature on Tuesday. Proposals for ...

User comments : 0