The role of dripping agent
The dripping agent is a nonionic surfactant having a hydrophilic group and a hydrophobic group, capable of migrating to the surface of the film, the hydrophobic group being super-introduced, and the hydrophilic group facing outward to increase the surface energy of the film; at the same time, After being compatible with the water droplets, the hydrophilic groups are directed toward the inside of the water, and the hydrophobic groups are arranged outward, which can lower the surface tension of the water. When the surface tension of the water is reduced to be equal to or less than the critical surface tension of the film, water can be spread on the surface of the film to form a water film instead of water droplets, thereby solving the problem of droplets. The surface tension of water at 25oC is: 72mN/m, and the surface tension of polyethylene film is: 31mN/m. It is obvious that water cannot be spread on the polyethylene film. However, after the addition of the drip agent, the surface tension of the water can be lowered to 25-30 mN/m, so that it can be spread on the polyethylene film. The mechanism of action is shown in the following figure:
The water film formed after unfolding does not obstruct the incidence of sunlight like water droplets, and the water film flows to the ground along the film surface due to its own weight, rather than falling on the crop.
The role of antifogging agent
In the early spring and late autumn, especially in the morning and evening, the temperature inside and outside the shed changes greatly, and the humidity is higher. The lowering of the temperature will cause the water vapor in the shed to be supersaturated and condense into fine droplets. When the speed of the droplets is greater than the speed of the fog, the fog will diffuse and will seriously hinder the penetration of the sun. Although the dripping agent can flatten the water droplets into a water film, it dissolves in the water layer and forms a tight arrangement in the water film, and the hydrophobic group faces outward, which hinders the absorption of the mist by the water film. Therefore, the dripping agent only has a dripping function and does not effectively eliminate the mist, and an anti-fogging agent is required at this time. Antifogging agent is a highly surface active surfactant, which can further reduce the surface tension of water to 15mN/m, so that the water film can be expanded into a thinner water layer and flow to the ground faster, thus improving the absorption of water layer. The efficiency of the droplets. At the same time, due to the characteristics of the anti-fogging agent, the space occupying effect disturbs the orderly arrangement of the dripping agent at the water film-air interface, thereby increasing the probability that the mist adheres to the water film and improves the probability. Defogging ability. Since the mist near the inner surface of the shed film can be quickly captured to form a thin water film and flow down the surface of the film, when the water vapor near the shed film changes from supersaturation to unsaturated, the mist disappears. At the same time, because the balance is broken, the mist in the shed will spread and migrate to the vicinity of the shed film, and will continue to be captured and adhered. Therefore, even if the temperature in the shed is lowered, the water vapor in the shed can be in an unsaturated state, thereby achieving the effect of eliminating the mist.
The dripping agent and anti-fogging agent are important additives for agricultural solar greenhouse membranes, and their effects are not the same, but the two complement each other, and the combined use can achieve a good effect of dripping and eliminating fog.