When spraying pesticides or fertilizers by machine, the droplet size differs. This is related to the use of different nozzles, pressure, speed, and one point maybe overlooked, the composition of the spray solution.
Usually there are three kinds of droplets which may lead to different spray results.
Spray particles'diameter below 150 microns: driftable droplet, if the diameter below 50 microns, the droplet is more likely to evaporate.
Spray particles'diameter between 150-500 microns: desirable droplet,if all droplets are uniform in this size, then more consistent coverage can be provided.
Spray particles'diameter above 500 microns: too large droplet, which is prone to bouncing or rolling off target surfaces.
Perfect spraying droplet performance is A.I. micelles evenly dispersed,droplet rightly reach the target surface(no evaporate or drift and no rebound),wetting and spreading on the leaf surface, lastly penetrating into the crop.
That is to say, to make the spraying droplet reach the target leaf is the first thing we should do!
There are variable drift control products on the market. Traditional ones are polymers like polyacryamide, polyethylene oxides, guar gum, xanthan gum, etc, which are of high molecular weight, water soluble and have relatively high viscosity.
It is obvious that the intrinsic viscosity may help produce an enhanced viscosity of the spraying solution, and tend to increase the droplet size and weight, thus decreases the quantity of driftable fines and improve the spraying application.
The phospholipid/lecithin-based chemistry is a new type of drift control product, such as LI-700 from Loveland. As the material is usually soybean derived, this kind of product is more environmental friendly than the traditional polymers. More importantly, the performance of drift control is much better.
The lecithin-based products also show outstanding results when compared to the drawbacks of polymer drift control products. The high molecular polymers tend to loose utility after undergoing mechanical stirring because of the degradation of polymer chain. And it may take a quite long time to make the polymers evenly disperse or dissolve in liquid solution, which increase the chance of spraying nozzle plug. And the polymers do nothing for the large sized droplets. In contrast, lecithin products can improve a uniform spray pattern, which really matters.
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The surface tension of silicone surfactant is much lower than the non-silicone ones, and this will lead to the big gap in the contact angle,generally positively related, see table as below.
Usually the contact angle is negatively related to the wetting speed and coverage diameter on the surface, see table as below.
Wetting speed and diameter:
PET is a hydrophobic surface.The good performance of silicone surfactant on such surface make it possible to have good market in agriculture.
The waxy layer of crop leaves are also hydrophobic. Genrally agrochemicals will find it hard to enter inside the leaf structure by stomatal absorption. And the wetting speed is slow, the spreading coverage is not big. The drops may slide off the leaf surface or big drop may even bounce out, thus leads to the pesticide waste and efficacy not meet the expectation.
With the help of silicone surfactant, the agrochemicals can spread on the leaf surface, then go into the small part of crops and weeds, and maximize the efficacy.