Pesticides microemulsions

WL Klotz, MR Schure, JP Foley. Determination of octanol-water partition coefficients of pesticides by microemulsion electrokinetic chromatography. J. Chromatogr. A 930 145-154 (2001). 

Microemulsion system applications span many areas including enhanced oil recovery, soil and aquifer decontamination and remediation, foods, pharmaceuticals (drug delivery systems), cosmetics, and pesticides [2,5,33,37,232,233]. Some of these are listed in Table 3.6. The widespread interest in microemulsions and use in these different industrial applications are based mainly on their high solubilization capac-... 

Microencapsulation can be used to provide a temporary barrier between a chemical species and its surrounding environment see also Section 14.3). This permits controlled (slow) release of the active agents following application. Depending on the product and the situation, an active ingredient such as a pesticide may need to be released slowly at low concentration, or slowly at high concentrations. Such controlled release can both reduce the number of crop applications that are required and also help prevent over use and subsequent run-off. The barrier can be provided by a polymer film, in the case of suspensions [867], or a liquid membrane, in the case of single or multiple emulsions [865], Microemulsions have also been used [234,865],... 

Surfactant aggregates (microemulsions, micelles, monolayers, vesicles, and liquid crystals) are recently the subject of extensive basic and applied research, because of their inherently interesting chemistry, as well as their diverse technical applications in such fields as petroleum, agriculture, pharmaceuticals, and detergents. Some of the important systems which these aggregates may model are enzyme catalysis, membrane transport, and drug delivery. More practical uses for them are enhanced tertiary oil recovery, emulsion polymerization, and solubilization and detoxification of pesticides and other toxic organic chemicals. 

It has been shown that the organophosphate ester tributylphosphate is very effectively solubilized by a microemulsion system incorporating CTAB and sulfolane as the emulsifier. The single-phase region in this system is similar to that obtained with CTAB and butanol as the emulsifier reported by Mackay (6). Thus it is expected that sulfone-containing microemulsions will solubilize other organophosphates and phosphonates such as pesticides and nerve agents. 

Emulson. [Auschem SpA] Ethoxyiated alkylphenoi or oils, sulfonates, or blends emulsifier, dispersant, wetting agent, solubilizer for pesticides, microemulsions. 

As green carrier oils or solvents - together with green surfactants - they also play a key role as inerts , i.e. non-active, inert formulation aids in modern crop protection, such as pesticide microemulsions or emulsifiable concentrates. Besides fatty acid esters, certain liquid fatty acid amides, more particularly capryl dimethylamide, are also increasingly creating interest as green solvents and carrier oils. 

Microemulsions, like micelles, are considered to be lyophilic, stable, colloidal dispersions. In some systems, the addition of a fourth component, a cosurfactant, to an oil-water-surfactant system can cause the interfacial tension to drop to near-zero values, easily on the order of 10 - 10 mN/m, allowing spontaneous or nearly spontaneous emulsification to very small drop sizes, 10 nm or smaller. The droplets can be so small that they scatter little light, and the emulsions appear to be transparent and do not break on standing or centrifuging. Unlike coarse emulsions, microemulsions are thought to be thermodynamically stable. The thermodynamic stability is frequently attributed to transient negative interfacial tensions, but this, and the question of whether microemulsions are really lyophilic or lyophobic dispersions are areas of some discussion in the literature. As a practical matter, microemulsions can be formed, have some special qualities, and can have important applications in areas such as enhanced oil recovery, soil and aquifer remediation, foods, pharmaceuticals, cosmetics, herbicides, and pesticides (13,16,45,59-61). 

The presence of micelles or microemulsions will have significant effects on the biological efficacy of an insoluble pesticide. In the first instance, surfactants will affect the rate of solution of the chemical. Below the c.m.c., surfactant adsorption can aid wetting of the particles and, consequently, increases the rate of dissolution of the particles or agglomerates [8]. Above the c.m.c., the rate of dissolution is affected as a result of solubilization. According to the Noyes-Whitney relation [122], the rate of dissolution is directly related to the surface area of the particles A and the saturation solubility, Cg, i.e. 

While the TMA can take just about any form, there has been a trend of combining multiple functions into one package mix. This can result in a concentrated emulsion, suspoemulsion, or other intricate colloidal formulation. Just as has been seen in pesticide development, there is a similar trend to develop multiple function TMAs as microemulsions(6). 

Technology, regulatory pressure, and environmental concerns are combining to drive down application rates. Colloid science principles can be used to formulate systems with reduced particle size. For exanq>le, a microemulsion can be formulated to replace a concentrated emulsion. The reduced particle size should yield a more imiform pesticide application, and this should maximize efficacy. 

Another type of pesticide formulation is a suspoemulsion (47), in which one active ingredient is emulsified and another active ingredient is included in the continuous phase as a finely divided dispersion of solid particles. Although some work has also been done on microemulsion formulations of pesticides, they tend to be too expensive and have some stability problems with temperature changes and upon dilution. Their main advantage is the enhancement of efficacy by improved transport into the target organism. 

Uses Emulsiferfor pesticide microemulsions and emulsifiable cones. 

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