Surface Chemistry in Agriculture Applications

Surface chemistry in agriculture applications

Surface chemistry designs for sorptives in fertilizers and sorbents in Soils to achieve the optimized harvest.  Increasing the retention of nutrients by agricultural soils is of great interest to minimize losses of nutrients by leaching and/or surface charges. other applications of surface chemistry in agriculture will be seen in pesticide or insecticide designs.  The active ingredients in pesticide or insecticide products come from many sources. Some, such as nicotine, pyrethrum, and rotenone, are extracted from plants. Others have a mineral origin, while a few are derived from microbes. However, the vast majority of active ingredients are synthesized (man-made) in the laboratory. These synthetic active ingredients may have been designed by an organic chemist or discovered through a screening process of chemicals generated by various industries. Regardless of their source, pesticide active ingredients have different solubilities. Some dissolve readily in water, others only in oils. Some active ingredients may be relatively insoluble in either water or oils. These different solubility characteristics, coupled with the intended use of the pesticide, in large measure define the types of formulations in which the active ingredient may be delivered. It is preferable from the manufacturer’s perspective to use the active ingredient in original form, when possible (e.g., a water soluble active ingredient formulated as a water soluble concentrate). When this is not feasible, it may become necessary to alter the active ingredient in order to change its solubility characteristics. This would be done, obviously, in a manner that did not detract from the pesticidal properties of the active ingredient. Usually, an active ingredient will be combined with appropriate inert materials prior to packaging. A brief review of some basic chemistry terminology should prove helpful in understanding differences among the various types of formulations.

• Sorption– In some cases it may be necessary or desirable to adhere a liquid active ingredient onto a solid surface (e.g., a powder, dust, or granule). This process is called sorption and it can be accomplished by two possible mechanisms:

          – Adsorption—a chemical/physical attraction between the active ingredient and the surface of the solid.

          – Absorption—entry of the active ingredient into the pores of the solid. Solution A solution results when a              substance (the solute) is dissolved in a liquid (the solvent). The solute can be a solid or a liquid. The                      components of a true solution cannot be mechanically separated. Once mixed, a true solution does not                  require agitation to keep its various parts from settling. Solutions are frequently transparent.

• Suspension– A suspension is a mixture of finely divided, solid particles dispersed in a liquid. The solid particles do not dissolve in the liquid, and the mixture must be agitated to maintain thorough distribution. Most suspensions will have a cloudy appearance. The herbicide Spike 80W is formulated as a wettable powder. This product forms a suspension when mixed with water for application as a spray. Label information describes the need for sufficient agitation to keep the product dispersed in the spray tank.
• Emulsion– An emulsion is a mixture that occurs when one liquid is dispersed (as droplets) in another liquid. Each liquid will retain its original identity and some degree of agitation generally is required to keep the emulsion from separating. Emulsions usually will have a “milky” appearance. The insecticide Demon EC is formulated as an emulsifiable concentrate. The active ingredient is dissolved in an oil-based solvent. When the product is mixed with water, an emulsion is formed. An emulsifying agent in the formulated product helps prevent the emulsion from separating by surrounding the oil droplets that contain the dissolved active ingredient.