The Application of Nanodispersions to Agriculture
Abstract:Although nanotechnology appears to have been invented in the last two decades, the truth is that nanoparticles have been utilised in varying forms for many hundreds of years. The most commonly encountered nanoparticles are water-insoluble inorganic or metallic materials. Gold and silver nanoparticles are used to create the unbleachable and vibrant colours (reds are gold; yellows are silver) in the stained glass windows adorning many European churches and cathedrals. In modern times, titanium dioxide and silica nanoparticles have become widely used as fillers and colourants in plastics, and nanotechnology is responsible for many of the huge advances in communications and computing. So what is nanotechnology? A definition has yet to be fully agreed and, for the purposes of this article, the size range below 1 micron, ranging from 999 nanometres to as small as just 1 nanometre is discussed. This size range means very little until you have some points of reference. A human hair is approximately 100 microns (100,000 nm) in diameter. A red blood cell is approximately 1/10th the diameter of a human hair. The gold nanoparticles used in cathedral windows to produce bright red colours are approximately 1/2000th of the size of a red blood cell. Sometimes it is easier to compare dimensions rather than consider a decrease in size, so, if you take a spherical nanoparticle of 1 nm diameter and increase its size until it is the size of a football, the same multiple operating on the size of a typical football would produce a sphere the size of the Earth. One of the key impacts of a decrease in size is an increase in surface area. Imagine that you have a cube of material that is then cut half way along each axis to give 8 equal sized cubes. Each of these cubes has dimensions that are half that of the original cube. The surface area of each smaller cube is one-quarter that of the original cube, and because there are eight of them, the overall surface area has doubled. The additional surface area has come from the surfaces that were exposed when we cut the larger cube. The same relationship holds true for spheres – when we take a given amount of material, halving the diameter of spherical particles doubles the surface area. Nanotechnologies are not solely related to nanoparticles, but often include the control of surface roughness or the positioning of components with nanometre precision; however, it is the arena of nanoparticles that is the focus of this article. The solubility of an agrochemical has an impact on many important factors controlling the activity, acceptability, ease of handling, ease of formulation, cost and ultimately the viability of the final agrochemical product. Overcoming the poor solubility of useful organic compounds has been achieved by both processing and chemical routes across many industries. The use of water-miscible solvents to aid solubility or the inclusion of water-immiscible solvents to form emulsions, are two potential avenues that have been successfully employed. Although it is always possible to modify organic compounds chemically with the intention of increasing solubility often without compromising activity, this approach leads to new agrochemicals with unknown safety, environmental and toxicity profiles that must be registered to be commercialised and registration is expensive. Increasing solubility to a viable extent through molecular redesign may also result in an unacceptable reduction in activity and/or loss of selectivity. The ideal compound may simply be poorly soluble. The production of nanoparticle based formulations has been shown to increase the activity of am otherwise poorly dispersing product.
Document Type: Research Article
Publication date: August 1, 2010
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