Researchers from the Massachusetts Institute of Technology (MIT) have found that only 2 percent of the spray from pesticides used by farmers sticks to the plant. A relatively large portion bounces right off of the plants and lands on the ground. Then, it flows to streams and rivers, causing further pollution.
According to MIT News, MIT researchers Kripa Varanasi, an associate professor of mechanical engineering, graduate student Maher Damak, Seyed Reza Mahmoudi, a research scientist, and former postdoc Md Nasim Hyder wrote a paper about their project. It was published in the journal "Nature Communications."
The MIT researchers found a solution to the problem of liquid bouncing off of hydrophobic surfaces. They just combined two inexpensive additives to the spray. The project was developed in collaboration with the MIT Tata Center for Technology and Design.
Previously, reducing the droplet bounce rate relied on additives like surfactants, which are soap-like chemicals that decrease the surface tension of the droplets. This causes them to spread more. However, it only provided a small improvement.
The new approach divides the spray into two portions. Each portion receives a different polymer substance. One gives the spray a negative electric charge while the other causes a positive charge.
As a result, a hydrophilic (water-attracting) "defect" happens when two oppositely-charged droplets meet on a leaf surface. This allows the spray to stick to the surface and increases the retention of further droplets.
The MIT researchers found, when they began to study the problem, that droplet bouncing happens in a matter of milliseconds. This meant that countermeasures based on chemical properties did not have enough time to solve the issue.
"So we thought, what else can you do?" Varanasi explained. "And we started playing around with charge interactions."
The combination of two different polymer additives were able to "pin the droplets" to the surface while it was spreading. According to Varanasi, this was before the droplets start a retraction that leads to their bouncing off the surface.
