Interlock: how it controls fines and big drops

The chemistry behind low-drift InterLock is puzzling. How do they convert those big liquid globs into desirable medium-size droplets, while also amalgamating your misty fines into desirable medium-size droplets?

That’s a good question, and one WinField United researchers wish they could answer. Although it’s proven that InterLock does reduce spray drift, the company is continuing with aggressive research because it still doesn’t fully understand how the product works, admits Lillian Magidow, senior research manager for Winfield United.

They do know it functions differently than polymer adjuvants, which reduce fines by raising the viscosity of the entire spray pattern. A high viscosity heavy liquid reduces fines, but also increases the number of large droplets, which are not highly effective in delivering product to the target. They splatter when they hit a leaf, so some of the product ends up in the soil.

“InterLock is an oil emulsion product. When you look into a sprayer tank, you see mostly water, but you also see small oil droplets. That’s the InterLock emulsion,” says Magidow.

She says if you examine the spray coming out of a nozzle tip, you’ll see a liquid sheet that extends about an inch from the tip. As this liquid sheet moves away from the tip, it becomes unstable and begins breaking up into individual droplets that will become the spray pattern further down at the target plant.

“Sheet breakup determines the ultimate droplet size distribution within your spray pattern. The oil emulsion in InterLock perforates that sheet in a regular pattern. It gives the sheet a lace-like look when you see it through a high-speed camera.

“Our theory is these more regular perforations create a narrower range of droplet sizes as the spray gets further from the nozzle tip. With our cameras, you can see that if we spray just water, there’s a more chaotic breakup of the sheet. There’s no regular pattern. With no InterLock in the tank, sheet breakup is influenced more by water temperature and nozzle characteristics.”

Magidow explains that adding a drift-reduction polymer to the water creates a heavier thicker spray. It’s a much higher viscosity with much bigger droplets. When the sheet starts breaking up, it forms ligaments. She says ligaments form in all sprays. The time they exist before hitting their target determines droplet size. With polymer adjuvants, the heavier spray forces the ligament to exist longer before breaking up into smaller droplets. That’s how they reduce fine droplets.

But the price you pay is an overabundance of large droplets. Because InterLock is oil-based, it has a negligible change to the viscosity.

“So we have this tiny little micro world happening right at the spray tip, and it’s all happening in an incredibly short time frame. For example, thousands of these perforations form on the sheet in the time it takes to blink your eye.”

Magidow says the process does not happen at the molecular or atomic level, nor are there electrical currents or air movement involved. It’s all a matter of finding the right oils to form the emulsion.

“We’re pretty confident in our assessment of perforations versus ligaments. Tank mixes are complex. And there’s different things that happen when some products go through a certain type of nozzle. For instance, we’re still learning new things about Liberty, and look how long it’s been around.”

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